Mr.Joe

Malaysian Fungi - Photo Gallery-Malaysian Fungi

2009-08-12T22:28:00.001-07:00

Malaysian Fungi - Photo Gallery-Malaysian Fungi

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General morphology of insects

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Body divided into tagmata (regions)

i) Head
ii)Thorax
iii) Abdomen

biological control

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The amount of food for each species of course gives the extreme limit to which each can increase, but very frequently it is not the obtaining of food, but the serving as prey to other animals, which determines the average number of a species.
Darwin on the Origin of Species (1859)

Biological control when considered from the ecological viewpoint as a phase of natural control can be defined as the action of parasites, predators or pathogens in maintaining another organism's population density at a lower average than would occur in their absence
P. DeBach (1964, p. 6)

Genetic marker

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Genetic marker- A locus or karyotype that provides useful information about
distinctiveness of populations or taxa, or information useful in forensics,
etc. Information may come from allozymes, microsatellites, chromosomes,
or inherited morphological characters

Introgression

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Introgression is the flow of alleles from one species or sub-species Some species are endangered
due to genetic ‘swamping’ by interbreeding with abundant related species. Genetic analyses
can be used to detect introgression and hybrid individuals to another. Typically, hybridizations occur when humans introduce exotic species into the range of related rare species, or alter habitat
so that previously isolated species are now in secondary contact. Introgression is a threat to the genetic integrity of a range of canid, duck, fish, plant, and other species

Terminology

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Genetic diversity is the variety of alleles and genotypes present in the group under study (population, species or group of species).

The genetic composition of a population is usually described in terms of allele frequencies, number of alleles and heterozygosity

Polymorphic -The presence in a species of two or more alleles at a locus, e.g. A1 and A2.
Polymorphic loci are usually defined as having the most frequent allele at a frequency of less
than 0.99, or less than 0.95 (to minimize problems with different sample sizes).

Monomorphic -A locus in a population is monomorphic if it has only one allele present, e.g. A1.
All individuals are homozygous for the same allele. Lacking genetic diversity.

cDNA Cloning

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cDNA:

A single-stranded segment of DNA that is complementary to the mRNA of a coding DNA segment or of a whole gene.
It can be used as a probe (cDNA probe as opposed to a genomic probe) for the corresponding gene because it is complementary to coding sections (exons) of the gene.

DNA Cloning

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A. Cell-based DNA cloning

B. A plasmid vector for cloning

References

Brown, T.A.: Genomes. Bios Scientific Publ., Oxford, 1999.

Strachan, T., Read, A.P.: Human Molecular Genetics. 2nd ed. Bios Scientific Publishers, Oxford, 1999.

Primer

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Primer-a short oligonucleotide with a sequence complementary to the site of attachment on the single-stranded DNA, is used as a starting point

Automated DNA Sequencing

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A. Thermal cycle sequencing
-advantage of thermal cycle sequencing is that double-stranded DNA can be used as starting material
B. Automated DNA sequencing (principle)

References

Brown, T.A.: Genomes. Bios Scientific Publ., Oxford,c1999.
Rosenthal, N.: Fine structure of a gene—DNA sequencing. New Eng. J. Med. 332:589–591, 1995.
Strachan, T., Read, A.P.: Human Molecular Genetics. 2nd ed. Bios Scientific Publishers, Oxford, 1999.
Wilson, R.K., et al.: Development of an automated procedure for fluorescent DNA sequencing. Genomics 6:626–636, 1990.

DNA Sequencing

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A. Sequencing by chemical degradation

base-specific cleavage of DNA by dimethyl sulfate (DMS) and piperidine
Four different chemicals are used in four reactions, one for each base.
Each reaction produces a set of DNA fragments of different sizes. The sizes of the fragments
A double-stranded or singlestranded fragment of DNA to be sequenced is processed to obtain a single strand labeled with a radioactive isotope at the 5! end (1).
This DNA strand is treated with one of the four chemicals for one of the four reactions.

Dimethyl sulfate attaches a methyl group to the purine ring of G nucleotides. The amount of DMS used is limited so that on average just one G nucleotide per strand is methylated, not the others (shown here in four different positions of G). When a second chemical, piperidine, is added, the nucleotide purine ring is removed and the DNA molecule is cleaved at the phosphodiester bond just upstream of the site without the base. The overall procedure results in a set of labeled fragments of defined sizes according to the positions of G in the DNA sample being sequenced.. The four reaction mixtures, one for each of the bases, are run in separate lanes of a polyacrylamide gel electrophoresis. Each of the four lanes represents one of the four bases G, A, T, or C. T

B. Sequencing by chain termination

References:

Brown, T.A.: Genomes. Bios Scientific Publ., Oxford, 1999.
Rosenthal, N.: Fine structure of a gene—DNA sequencing. New Eng. J. Med. 332:589–591, 1995.
Strachan, T., Read, A.P.: Human Molecular Genetics. 2nd ed. Bios scientific Publishers
http://en.wikipedia.org/wiki/DNA_sequencing
http://www.springerprotocols.com/Abstract/doi/10.1385/0-89603-248-5:261

Chemoreception

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Chemoreception, essentially taste (contact chemoreception) and smell (distance chemoreception), is an extremely significant process in the Insecta, as it initiates some of their most important behavior patterns, for example, feeding behavior, selection of an oviposition site, host or mate location, behavior integrating caste functions in social insects, and responses to commercial attractants and repellents.

Though taste and smell are distinguished traditionally, such a distinction has no firm morphological or physiological basis. The sensilla for the two senses are structurally very similar; indeed, in some species the same structure is used for both olfaction (smell) and gustation (taste). Further, stimulation of a sensillum by either tastes or odors probably entails comparable subcellular or molecular interactions. Any difference between smell and taste is, then, a matter of degree. Smell may be defined as chemostimulation by compounds in very low concentration but volatile at physiological temperatures, and taste as chemostimulation by higher concentrations of liquids that are not volatile at physiological temperatures.

In addition to taste and smell, insects have a third method of detecting chemical stimuli, the common chemical sense. This is the response of an insect (always an avoiding reaction) to high concentrations of noxious chemicals. It is not a response caused by stimulation of normal chemosensilla, because the response is not abolished after surgical removal of the structures bearing these sensilla. It would seem to be a non-specific response of other types of sensory neurons.

Mechanoreception

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Insects receive and respond to a wide variety of mechanical stimuli. They are sensitive to physical contact with solid surfaces (touching and being touched); they detect air movements, including sound waves; and they have gravitational sense, that is, through particular mechanosensilla they gain information about their body position in relation to gravity. This is especially important in flying or swimming insects which are in a homogeneous medium; they receive information about their body posture and the relationship of different body components to each other, and they obtain information on physical events occurring within the body, for example, the extension of muscles in movement, the filling of the gut by food, and the stretching of the oviduct when mature eggs are present

Summary of cuticle formation during the molt/intermolt cycle

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(A) Secretion of ecdysial droplets.
(B) Pinocytosis and apolysis of plasma membrane.
(C) Redifferentiation of plaques and cuticulin envelope deposition.
(D) Cuticulin envelope complete and digestion of old cuticle.
(E) Secretion of inner epicuticle and bucking of cuticulin envelope.
(F) Beginning of procuticle secretion.
(G) Cuticle immediately after ecdysis.
(H) Cuticle after tanning.

The cuticulin envelope

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(1) It is a selectively permeable barrier. During breakdown of the old cuticle, it allows the “activating factor” f for the molting gel to move out and the products of cuticular hydrolysis to enter, yet it is impermeable to the enzymes in the molting fluid. It is permeable to waxes (as these are deposited only after the cuticulin layer has formed) and, in some insects, it permits the entry of water.
(2) It is inelastic and, therefore, serves as a limiter of growth.
(3) It provides the base on which the wax monolayer sits. The nature of the cuticulin envelope will therefore determine whether the wax molecules are oriented with their polar or nonpolar groups facing outward and, therefore, the surface properties of the cuticle.
(4) It plays a role in determining the surface pattern of the cuticle.
(5) It is resistant to abrasion and helps prevent infection.
(6) It is involved in production of physical colors

The chemical structure of chitin

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References:

Entomology-3rd Edition (Cedric Gillot, Springer 2005)

The procuticle

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Procuticle is composed almost entirely of protein and chitin. The latter is a nitrogenous polysaccharide consisting primarily of N-acetyl-D-glucosamine residues together with a small amount of glucosamine linked in a β1,4 configuration.

The procuticle (= fibrous cuticle) forms the bulk of the cuticle and in most species is differentiated into two zones:

endocuticle
exocuticle

The border between the two zones is not clear and an intermediate area, the mesocuticle, is visible

The endocuticle:

composed of lamellae (is made up of a mass of microfibers arranged in a succession of planes, all fibers in a plane being parallel to each other).

The exocuticle:

The region of procuticle adjacent to the epicuticle that is so stabilized that it is not attacked by the molting fluid and is left behind with the exuvium at molting
Exocuticle is absent from areas of the integument where flexibility is required, for example, at joints and intersegmental membranes, and along the ecdysial line. In many soft-bodied endopterygote larvae the exocuticle is extremely thin and frequently cannot be distinguished from the epicuticle and cuticulin envelope

The cuticle of insect

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The cuticle, which is mainly produced by the epidermal cells, usually includes three
primary layers:

the inner procuticle
middle epicuticle
outer cuticulin envelope

The stucture of insect

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The basal lamina:

The innermost component of the integument
An amorphous but selectively porous acellular layer that is attached by hemidesmosomes to the epidermal cells
It is up to 0.5 μmthick and is produced mainly by the epidermis
The chemical nature of the basal lamina is poorly understood though neutral mucopolysaccharide, glycoproteins, and collagen

The epidermis (hypodermis):

More or less continuous sheet of tissue, one cell thick
Responsible for secreting the bulk of the cuticle
Its cells are flattened and intercellular boundaries are indistinct-During periods of inactivity
The cells are more or less cuboidal, and their plasma membranes are readily apparent; one to several nucleoli, extensive rough endoplasmic reticulum, and many Golgi complexes are evident-During active
At metamorphosis, the epidermal cells develop basal processes (“feet”) which can extend to become connected with the basal lamina and with other epidermal cells
Epidermal cells also possess the ability to develop various forms of cytoskeletal extensions which can be used, for example, to draw tracheoles closer to the cell for increased oxygen supply, or to maintain intercellular contact as the cells migrate during wound healing and changes in body shape
The cells often contain granules of a reddish-brown pigment, insectorubin, which in some insects contributes significantly to their color

The Integumnet of Insect

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The integument of insects (and other arthropods) comprise:

Basal lamina
Epidermis
Cuticle

The function of Integument:

It provide physical protection for internal organs
It serves as a skeleton to which muscles can be attached
It also reduces water loss
It acts as a metabolic reserve, to be used cyclically to construct the next stage, or during periods of great metabolic activity or starvation
It prevents entry of foreign material, both living and nonliving, into an insect
The waxy outer layer serves as a repository for contact sex pheromones
The color of insect

The Queen of Termites

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Physogastric queens - females whose abdomen becomes enormously swollen through hypertrophy of the ovaries and consequent stretching of the intersegmental membranes the abdomen is pale, and the original tergal and sternal plates are the only areas of sclerotization.

The head is round or oval and carries well-developed compound eyes, moniliform antennae with a varied number of segments (generally fewer in more advanced termites), and mandibulate mouthparts

Three castes of termite

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reproductive (primary and secondary; both male and female)
soldier (sterile adults of both sexes)
worker ( sterile adults of both sexes)

Isoptera

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Common names: termites, white ants

Polymorphic social insects living in colonies that comprise reproductives, soldiers, and workers; head with moniliform multisegmented antennae and mandibulate mouthparts, compound eyes present but frequently degenerate, ocelli often absent; wings when present almost identical (except Mastotermes) and membranous, lying horizontally over abdomen at rest, capable of being shed by a predetermined basal fracture, legs identical and with a large coxa, tarsi almost always four-segmented (five-segmented in Mastotermes); cerci short and with few segments, external genitalia lacking in both sexes of most species.

References:

Entomology-3rd edition Cedric Gillot, Springer 2005

Suborder Anisoptera (Dragonflies)

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A dragonfly,Macromia magnifica (Corduliidae). (A) Adult male; (B) larva, dorsal view; and (C) larva, lateral view with labium extended.

Suborder Anisoptera (Dragonflies)

Distinguishing features of dragonflies include fore andhindwings dissimilar in venation and, usually, shape; discoidal cell divided into two triangular areas; eyes contiguous or nearly so; and larvae stout and without caudal lamellae.

Zygoptera (Damselflies)

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A damselfly, Ischnura cervula (Coenagrionidae). (A) Adult male; and (B,C) larva, dorsal and lateral views
*Notes on the life history and ecology of the dragonflies (Odonata) of Washington and Oregon

Zygoptera (Damselflies)

Damselflies are characterized by the following structural features: fore and hind wings
almost identical in shape and venation, quadrangular discoidal cell never longitudinally
divided, eyes far apart, and larvae with three (rarely two) caudal lamellae.

Identification of Insect

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There are various methods for identifying organisms:

(1) the specimen may be sent to an expert
(2) it may be compared with the specimens in a labeled collection,
(3) it may be compared with pictures or descriptions
(4) it may be identified by use of a key

Superclass Hexapoda.

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1. CLASS. Collembola
ORDERS. Arthropleona, Neelipleona, and Symphypleona
2. CLASS AND ORDER. Protura
3. CLASS AND ORDER. Diplura
4. CLASS. Insecta
I. SUBCLASS. Apterygota
ORDERS. Microcoryphia and Zygentoma
II. SUBCLASS. Pterygota
A. INFRACLASS. Paleoptera
ORDERS. Ephemeroptera and Odonata
B. INFRACLASS. Neoptera
a. DIVISION. Polyneoptera (orthopteroid orders)
ORDERS. Orthoptera, Grylloblattodea, Dermaptera, Plecoptera,
Embioptera. Dictyoptera, Isoptera, Phasmida,
Mantophasmatodea, and Zoraptera
b. DIVISION. Paraneoptera (hemipteroid orders)
ORDERS. Psocoptera, Phthiraptera, Hemiptera, and Thysanoptera
c. DIVISION. Oligoneoptera (endopterygote orders)
ORDERS. Mecoptera, Lepidoptera, Trichoptera, Diptera. Siphonaptera,
Neuroptera, Megaloptera, Raphidioptera, Coleoptera,
Strepsiptera, and Hymenoptera

Systematics and Taxonomy

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Systematics may be defined as the study of the kinds and diversity of organisms and the relationships among the.

Taxonomy, the theory and practice of identifying, describing, naming, and classifying organisms, is an integral part of systematics.

Classification is the arrangement of organisms into groups (taxa, singular taxon) on the basis of their relationships

Classification

Biological systems of classification are hierarchical, that is, the largest taxa are subdivided into successively smaller taxa. Thus, each taxon has a particular level (rank) within the system. Groups of the same rank are said to belong to the same taxonomic category, to which a particular name is given. Some of these categories are obligatory (capitalized in the example below), while others are optional. To show the hierarchical arrangement and to introduce the names of the various categories, let us take as an example the classification of the honey bee, Apis mellifera:

KINGDOM Animalia
PHYLUM Uniramia
Subphylum Hexapoda
CLASS Insecta
Subclass Pterygota
Infraclass Neoptera
Division Oligoneoptera
ORDER Hymenoptera
Suborder Apocrita
Superfamily Apoidea
FAMILY Apidae
Subfamily Apinae
Tribe Apini
Subtribe —
GENUS Apis
Subgenus —
SPECIES Apis mellifera
Subspecies-

Typical Chewing Mouthparts

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Structure of (A) mandible, (B) maxilla, and (C) labium of a typical chewing insect. [From
R. E. Snodgrass, Principles of Insect Morphology.

Types of antennae

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*A General Textbook of Entomology, 9th ed.

Postgenital Segments of a Female Grasshopper

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The postgenital segments include the 10th and, when present, the 11th abdominal segments. In the lower orders where both postgenital segments are present, the 10th segment is usually united with the 9th or 11th segments and it never bears appendages. The 11th segment comprises a somewhat triangular tergal plate, the epiproct, and a pair of ventrolateral plates, the paraprocts. It bears appendages, the cerci, inserted in the membranous area between the 10th and 11th segments on each side of the body.

The Abdomen of Insect

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The Abdomen

The abdomen differs from the head and thorax in that its segments generally have a rather simple structure, they are usually quite distinct from each other, and most of them lack appendages. The number of abdominal segments varies. The primitive number appears to be 12, though this number is found today in only the Protura. Most insects have 10 or 11 abdominal segments, but several of these are reduced. The reduction occurs primarily at the posterior end, but in some endopterygotes the first segment is reduced and intimately fuse with the metathorax. For the purpose of discussion the abdominal segments may be considered to form three groups: pregenital segments, genital segments, and postgenital segments.

Leg Modifications of Insect

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Jumping-In Orthoptera and a fewColeoptera (e.g., flea beetles) the femur on the hindleg is greatly enlarged to accommodate the extensor muscles of the tibia used in jumping
Swimming-The tibia and tarsus of the hindlegs (occasionally also the middle legs) are flattened and bear rigid hairs around the periphery.
Grasping-Legs modified for grasping are found in predaceous insects such as the mantis and giant water bug, in ectoparasitic lice, and in males of various species where they are used for hanging onto the female during mating
Digging-The legs are large, heavily sclerotized, and possess stout claws. The tarsomeres are
reduced in number or may disappear entirely in some forms(e.g.,cicadas and various beetles)
Sound production-In many Orthoptera sounds are produced when the hind femora, which have a row of cuticular pegs on their inner surface, are rubbed against ridged veins on the fore wing
Cleaning-A notch lined with hairs occurs on the metatarsus of the foreleg through which the antenna can be drawn and cleaned (e.g.,certain Coleoptera and Hymenoptera, for example, the honey bee)
Pollen collection-Rows of hairs, the comb, on the inner side of the first tarsomere scrape pollen off the abdomen. The rake, a fringe of hairs at the distal end of the tibia, then collects the pollen from the comb on the opposite leg and transfers it to the pollen press. When the press is closed, the pollen is pushed up into the pollen basket, where it is stored until the bee returns to its nest

Structure of an antenna

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Reference:
R. E. Snodgrass, Principles of Insect Morphology

Structure of the typical pterygotan head

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Agriculture in a nest of termite

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Termites use the organic matter from rotten leaves and pieces of wood as soil for fungus. Mixing it with secretions, they use it to grow fungus in specially organized spacious storage rooms.

In oder to ensure the productivity of their fungus grades and for the health of the colony in general, temperature and humidity in the mounds must be kept constant. The growth of the fungus raises the temperature around it to a point that could ruin the temperature balance created in the nest; this elevation in temperature must be corrected at all costs. So termites install a ventilation system to manage the heat they produce by themselves and through the metabolism of the fungus in their gardens.

Termite injurious to coconut palm, Kuala Terengganu

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I took this picture during my trip to University of Malaysia Terengganu. I was quite surprised that there were so many of coconut palms along coastline of UMT had been attacked by termites. The termites work through the base of the nut or by an attack on the collar, and wilting of the central shoot is the first sign of attack.

*In grown up palms termites usually attack the roots and up to about 15 cm of the stem.
The common species of termites which attack the coconut palms are

Odontotermes redemani
Hypotermes obscuriceps

*References:

ML Roonwal 1979. Termite Life and Termite Control In Tropical South Asia.

Nest of Termite

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Nest of Termite at Bangi Forest-Fernarium UKM Bangi.-taken by Johari Jalinas
Termites use grains of sand, earth and pieces of wood to construct their nests. They mix these materials with their own secretions to produce a strong mortar. Some termite species use clay to build their nests. Obviously, termites cannot manage these things with their own intelligence; their activities are inspired in them by God.-Harun Yahya's Book (Miracle of Termite)

Termites are best known for their ability to build magnificent nests out of the ground more skillfully than a human being could. The skill of these tropical architects is undisputed in building cities that seem to appear out of nowhere. Their ease in finding building materials and technical skills are amazing. Every species of termite builds different kinds of nests suitable to their needs. These nests can be found inside trees, on or under the ground.

Nests that are shaped like mountains are architecturally very complex. The construction of all the nests begins underground, where compartments become more spacious as they approach the surface. A cross-section of a termite nest would show that the inside resembles a sponge composed of countless cells 2.5 cm (0.9 inches) in size, or smaller. These cells are joined by narrow passages only large enough for termites to pass through. Termites thrive in an atmosphere whose temperature and humidity are constant, with a carbon dioxide content of between 5 and 15%.

Reference:
A miracle of termite by Harun Yahya.

Termite Colony

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Termite Prevention

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A lot of termite control products are toxic to termites, very few of the termites are actually killed before being repelled by the termiticide barrier. As a result, termites remain alive and actively seek gaps in the barrier in order to gain access to the building.

Detail:
Termidor in Sydney - Termite Prevention
By Bruce Gow

NEMATODE IN BIOLOGICAL CONTROL

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Nematodes

A. Several entomopathogenic nematode families (Mermithidae,

Steinernematidae, Heterorhabditidae) contain species that are parasites of

insects during at least part of the nematodes development.

B. Normally, they have 4 molts between the egg and adult stages and

between stages are referred to as juveniles.

C. Most nematodes infect insect hosts as infective stage juveniles.

1. They may enter through the host cuticle or through the midgut

2. After entrance into the hemocoel, juvenile undergoes a period of rapid

growth, then leaves the host, enters the soil and molts to form the

adult nematode

D. Mating and oviposition occur external to the host in the Mermithidae.

E. Some species kill their hosts upon leaving.

F. Some species transport bacteria when they enter the cavity of the host

and the insect dies from bacterial septicemia and the nematode feeds on

the bacteria in the dead host tissue.

G. Most nematodes are difficult to culture on artificial media.

H. Only obligate endoparasitic nematodes are found in the genus

Steinernema (= Neoaplectana).

References:

INSECT PATHOLOGY IN BIOLOGICAL CONTROL
Lynn M. LeBeck, University of Hawaii at Manoa

Respiration of Nematode

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Respiration takes place through the cuticle and circulation is obtained by the continuous movement of the body

References:

J.Kalamakoff, J.F.Longworth. 1980. Microbial control of insect pests: New Zealand Department of Scientific and Industrial Research .P(83)

Nematodes in insect control

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To evaluate the significance of a nematode to an insect, the following should be investigated

the identify of the nematode species
the biology and life cycle of the nematode
the ability of the nematode to kill the insect
method for mass rearing
procedures for field testing
formulation and processing of the nematode into a product suitable for large-scale field application.

References:

J.Kalamakoff, J.F.Longworth. 1980. Microbial control of insect pests: New Zealand Department of Scientific and Industrial Research.P(83)

Estimating Disease Mortality

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Two approaches to this problem:

specimens may be reared for a specified time after which the number of dead individuals can be counted and the cause of death diagnosed
infection may be diagnosed immediately after collection (or specimens may be frozen at the time of sampling for later examination)

Estimating disease mortality from specimens reared for specified times.

The objective of this approach is to rear specimens from quantitative field samples for a set period, under conditions which duplicate the natural habitat as closely as possible.

Mortality is assessed from the number of insects dying during the time concerned and assigned to its various causes from the results of diagnostic tests.

Specimens should be reared individually, in disease-free conditions, to avoid cross-contamination

The advantage of this method lies in its simplicity. Direct estimates of mortality are obtained with a minimum of ancillary experimentation.

However, there are several serious disadvantages. Many delicate insects, particularly larvae of soil-inhabiting species, are inevitably damaged during collection and die later from injury or wound infection. Further, it is difficult to duplicate the environmental conditions of the natural habitat and microclimatic changes may accelarate or retard disease development

References:

J.Kalamakoff, J.F.Longworth. 1980. Microbial control of insect pests: New Zealand Department of Scientific and Industrial Research .P(10-11)

Total mortality study

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Data Collection:

initial number of insects (e.g number of newly hatched larvae)
number of insects killed by disease
number of healthy adults and the number of diseased adult
number of progeny produced by healthy adults and the number produced by diseased adults

References:

J.Kalamakoff, J.F.Longworth. 1980. Microbial control of insect pests: New Zealand Department of Scientific and Industrial Research .P(10)

The research programme-Integrated Pest Control

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The research programme has three major components:

Short-term research studies problems requiring urgent solution, such as pest resistance to pesticides. Continued satisfactory chemical control is essential while integrated control programmes are being developed.
Medium to long term research includes modification of existing chemical methods (I) In a "supervised spray programme" where all key pests are monitored(ii) by the use of pheromones to guide insecticide applications (iii) combination with selective insecticide
Long-term Research centres on(iv) selective insect control, by replacement of the offending broad-spectrum insecticides

References:

J.Kalamakoff, J.F.Longworth. 1980. Microbial control of insect pests: New Zealand Department of Scientific and Industrial Research .P(9)

Biological Control

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Parasites and predators
Pathogens
Crop plants resistant to the pest
Insect pheromones-widely used as attractants in field traps which provide a guide to the changes in a developing pest population and indicate when insecticides should be applied

References

J.Kalamakoff, J.F.Longworth. 1980. Microbial control of insect pests: New Zealand Department of Scientific and Industrial Research P(7)

The general approaches to pest control

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They are:

the administrative or legislative approach
the approach through husbandry or management techniques
the use of chemicals
the manipulation of biological control

References: P(3)

J.Kalamakoff, J.F.Longworth. 1980. Microbial control of insect pests: New Zealand Department of Scientific and Industrial Research

Cellular Encapsulation

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Encapsulation generally occurs when a particle, pathogen, or parasite is too large to be engulfed by an individual cell. The hemocytes collect and surround the large particle and then adhere to its surface, usually forming a dense covering. There is generally an intra-and extracellular deposition of the black pigment, melanin. The entire structure is called a capsule.

Encapsulation takes place in two distinct phases (Ratcliffe 1976)(Gupta 1985)

First, hemocytes (granulocytes and /or coagulocytes) aggregate around a foreign object
the hemocytes lyse and release subtances in the hemolymph attracting other hemocytes (mainly plasmatocytes) that complete the formation of the capsule. A surface recognition phenomenon of self and nonself, as in the case of phagoctosis, may be involved in attachment and encapsulation (Salt 1960,1968)

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(513-514)

Process of Phagocytosis

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Phagocytes ingest particles in at least three ways:

by formation of pinocytotic vesicles to engulf fluid that contains small particles
by encircling the particles with pseudopodia
by close contact and spreading of the plasma membrane (Salt 1970)

The process of phagocytosis involves the following steps (Whitcomb 1974, Gotz and Boman 1985)

Recognition by hemocytes of the presence of foreign bodies occur in insects, but how the hemocytic activity is induced is still unknown.
Chemotactic attraction is involved where hemocytes are attached to foreign bodies. The existence of this stage is still not completely resolved.
The attachment phase occur when the particulate matter adheres to the cell surface. This may involve physicochemical forces or the receptor molecules of foreign bodies attaching to binding sites on the hemocyte surface (Young 1985). Opsonins may be involved (Brookman 1988)
Ingestion occurs with pseudopodia or by membrane invagination to surround and enclose the particle. In the cytoplasm, the particle is contained in a phagocytic vacuole, the wall of which is the original cell membrane.
Degranulation results from the release of enzymes from granules (lysosomes) into the phagocytic vacuole.
The digestion of particles occur by lysosomal enzymes, and the undigestible particles are released by exocytosis.

Function of Hemocytes

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The functions:

blood coagulation-immune reaction because it is involved in wound healing and may exclude the invasion of pathogens.Two physiologically distinct processes:a) cellular agglutination or coagulation b) plasma coagulation. Coagulation resulting from lysis of hemocytes with a granular plasma precipitate is currently attributed to a specific type of hemocyte, the coagulocyte. These cells undergo very rapid and selective changes during coagulation. These cells undergo very rapid and selective changes during coagulation. The reaction of the coagulocyte plasma membrane to foreign surfaces differs from those of other hemocytes (Goffinet and Gregoire 1979). The plasma membrane tends to develop microruptures, accompanied by the ejection of cytoplasmic material and the clotting reaction of the surrounding plasma. This difference may explain the functional contrast between active coagulocytes and other hemocytes, at least at the beginning of coagulation. Coagulocytes tend to break down when blood is removed from an insect, and only the nuclei remain intact on the slide. Other hemocytes that break down but may not function in coagulation. Coagulocytes tend to break down when blood is removed from an insect, and only the nuclei remain intact on the slide. Other hemocytes that break down but may not function in coagulation are the spherulocytes, granulocytes, and oenocytoids. Barwig and Bohn (1980) have detected in the blood of the cockroach Leucophaea maderae two proteinaceous coagulogens, one contained in hemocytes and the other in plasma. They suggest that clotting is initiated by the disintegration of hemocytes and the release of their coagulogen, which forms a soft gel around the cells. Immediately after the release of the hemocyte coagulogen, it reacts with the plasma coagulogen to form a rigid clot.

phagocytosis
encapsulation
detoxification
storage and distribution of nutritive materials

References:
Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(511)

Hemocytes

2008-05-12T08:28:00.000-07:00

Hemocytes are a complex of several types of cells that circulate within the hemolymph but are sometimes attached loosely to other tissues or are enmeshed within them.

Characteristics and Functions:

do not transport O2
nucleate cells
forms-amoeboid and pleomorphic

Three well-defined types of hemocytes in most insects

prohemocytes-(Arnold 1972,Gupta 1979) are small, round or ellipsoidal cell (6um wide by 6 to 14um long). with large, round, centrally located nucleus (3.6 to 12um) surrounded by a thin rim of cytoplasm. They are germinal cells and are considered to be the main source of postembryonic hemocyte multiplication. They are stem cells that give to the other main categories of hemotocytes. They occur, in most stages of an insect, as only a small part of the total hemocyte population
plasmatocytes- very greaty in size (3.3 to 5.5 um by 3.3 to 40 um) and are highly pleomorphic. The round to ovoid nucleus iis generally centrally located. Scattered chromatin masses and a nucleolus may be present.Plasmatocytes are usually prominent in size and abundant in numbers and form the basic type of hemocyte in most insects (Gupta and Sutherland 1966). They generally resemble the prohemocytes; typical and macrophagous. The typical plasmatocyte is often regular, sometimes discoid, and poorly differentiated. In the hemocoel, it forms capsules around large foreign bodies but does not phagocytize particles. It seems to occur only in Lepidoptera and Diptera. The macrophagous plasmatocyte is a large polymorphic cell with numerous didgitations (pseudopodia). It is phagocytic and rapidly engulfs foreign material injected into the blood as well as tissue debris. It sometimes occurs in capsules when part of the foreign material can be phagocytized.
granulocytes-are compact cells of variable sizes(10 to 45 um by 4 to 32um) and shapes, generally round or disc-shaped, with relatively small, usually centrally located, round or ovoid nuclei (2 to 8 um by 2 to 7 um). Micropapillae may occur on the plasma membrane. The large volume of cytoplasm characteristically contains many, mostly small, round granules. Granulocytes have some ultrastructural features similar to plasmatocytes but are characterized mainly by membrane-bounded, electron-dense, or granular bodies in the cytoplasm. Several types of membrane-bound granules occur in various insects (Costin 1975,Gupta 1985). Some granules are structureless and electron dense, other are structures and contain microtubules. Granulocytes may contain lipid droplets, especially in older cells. The cytoplasm of the granulocyte has abundant free ribosomes (polysomes), golgi bodies, both smooth and rough endoplasmic reticula, and lysosomes. Generally, mitochondria are few in number. They vary in insects from amoeboid to nonmotile forms and are easily misidentified. In some insects, they are phagocytic but not in others.

Four other types in many insects

coagulocytes
spherulocytes
adipohemocytes
oenocytoids (Gupta 1979)

References:P(509-510)
Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.

Hematology Study on Insect

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In addition to the defense mechanisms described above, an insect is able to resist the development of disease even after the microorganism has entered its hemocoel.

Such resistance is associated with cellular reactions and acellular (humoral) responses.

cellular immunity is mainly involved with blood cells (hemocytes)
humoral factors may be involved in cellular activities, such as phagocytosis and encapsulation

Blood or hemolymph comprises about

10-40% of the volume of an insect's body
fluid portion or plasma
blood cells or hemocytes

The process of cell multiplication and differentiation is called hemopoiesis. Usually very few circulating cells in the hemolymph are seen undergoing mitosis except under stress conditions, such as injury.

The cells that divide are mainly prohemocyte and plasmatocyte, and possibly granulocyte, adipohemocyte, and spherulocyte (Arnold 1974)

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(507)

Life Cycle of Steinernematids

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Dauer juveniles are ingested by a susceptible host and enter the hemocoel by penetrating directly through the midgut or enter through the spiracles and penetrate the tracheae.

Once in the hemocoel, the dauer juvenies release the associated bacterium through their anus. The bacterium multiples rapidly in the host's body and causes host death by septicemia within 48 hours. The nematodes develop rapidly to the adult stage, mate, and produce eggs.

First-stage juveniles emerge from the eggs and become adults; in small hosts, however, they may become dauer juveniles. The progeny from these first generation adults (or later generations in larger hosts) becomes dauer juveniles. Cues for dauer juvenile formation appear to be high nematode density, suggesting the presence of a pheromone, and low-soluble nutrient status in the cadaver (Popiel 1989). If adequate moisture is present, the dauer juveniles leave their host. In the laboratory, they exit from the host 8-14 days after infection. The dauer juveniles can remain alive for a long period of time and, under laboratory conditions, some will live 5 years.

Matricidal endotoky occurs (i.e, in older adult females). The eggs hatch within the body, and the juveniles feed on the body contents of the mother. These dauer juveniles escape through the oral and anal openings of the dead female.

The nematode needs the associated bacterium for its growth and development, and the bacterium needs the nematode to invade an insect(Dutky 1959). The nematode kill its host without its associated bacterium but unable to reproduce, and the bacterium cannot invade the hemocoel of its host without the nematode.

S. carpocapsae along with its associated bacterium has been grown on media with pork kidney-peptone agar (Dutky 1964). Because the bacterium is present, the nematode is grown monoxenically.

Glaser was the first to culture a nematode on an artificial medium. This nematode, Steinernema glaseri, is now grown axenically on a defined diet and useful information has been obtained on its dietary requirements (Jackson and Platzer 1974)

Insects infected with steinernematids are slightly discolored and flaccid and remain intact.

Upon dissection, the tissues have a gummy consistency and do not have a putrid odor. Secondary microorganisms are usually not present in great numbers because the associated bacterium produces an antibiotic,

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(475-478)

Nematode-Steinernematidae

2008-05-12T06:52:00.003-07:00

Steinernematidae:

Represntatives of his family offer much promise as biological control agents because of their high virulence and broad host range. Steinernerma carpocapsae, for example, kills its hosts within 48 hours and will infect many insect species in the laboratory and field (Poinor 1979). A number of Steinernerma species have been described from natural infections of insects, and all have a mutualistic association with bacteria (Dutky 1959;Thomas and Poinar 1979). The bacteria, in the genus Xenorhabdus have been studied in great detail (Poinar and Thomas 1965). As an example, the bacterial symbiont Xenorhabdus nematophilus produce two colony forms, designated as

phase one (primary form)-is isolated from infective nematodes and tends to be unstable, converting to phase two.
phase two(Secondary form)-is isolated from old insect cadavers or in vitro culture of nematodes.

Other differences between in phase one, and nematode reproduction in -vitro.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(475)

Behavioral Effects

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Abnormal behavior in insects is usually manifested late in nematode infection.
For example:

Alfafa weevils infected with Hexamermis have diificulty in crawling and orienting themselves (Poinar and Gyrisco 1962)
Worker ants infected with mermithids show a high degree of negative phototropism compared with uninfected ants (Wheeler 1928).
Infected ants do not feed immature ants and appear to be in a chronic state of hunger.
Superinfection of mermithids affects the flight of the desert locust (WeisFogh 1956) and the activity of mosquito larvae (Welch 1960)

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.p(469-471)

Internal Effects

2008-05-12T00:58:00.000-07:00

Nematodes in the hemocoels of insects cause many physiological changes, and these changes have been recorded from a number of different insect groups.

The presence of mermithids result in

Sterility eg: reduced ovaries
Ultimately death of the insects
inhibit the molting
reduced in hemolymph
decreasing fat body synthesis
increase in blood uric acid
reduced fat-body content
retarted development of the reproductive organs in both sexes
reduced the gland secretion
hemolymph composition and oocyte development are affected
trehalose levels are not affected , but hemolymph proteins are reduced
damage to certain gland

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.
P(468-469)

External Infection

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Insect generally show

little external evidence of a nematode infection
even when external anomalies are observed, a dissection of the host or the emergence of the nematode is necessary to confirm a nematode infection.
the number of the nematodes infecting an insect or the age of the host at time of infection often determines whether external anomalies occur.

In mermithids, the infections usually manifest greater external morphological changes than in the other nematode groups.eg:

mermithid Hexamermis arvalis may have malformed elytra (Poinar and Gyrisco 1962). The infected weevil larvae are yellow-green compared with the dark green of uninfected larvae.
In black fly larvae, the mermithid infection may cause distorted abdomens (Phelps and DeFoliart 1964)

Nematode Infection

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Pathology in insect hosts caused by nematode infection may be manifested

Externally-pathological effects are expressed by morphological changes
Internally- Alterations in morphology and physiology
Behaviorally- Insects infested with nematodes often show aberrant behavior. In some instances, such as a mermithid or a steinernematid, the host insect is killed; in others, such as an allantonematid or a sphaerulariid infection, the host insect becomes sterile or has reduced fecundity.

Host Resistance

2008-05-11T23:51:00.000-07:00

An insect resists nematode infection through:

behavioral-the insect actively avoids or repels the nematode e.g: active mosquito species had a lower prevalence of infection by the mermithid Romanomermis culicivorax

physical- the nematode cannot penetrate the intergument or the cocoon of a host insect. e.g: Romanomermis culicivorax has difficulty in penetrating the intergument or older mosquito larvae (Petersen and willis 1970). Dauer juveniles of Steinernema carpocapsae cannot penetrate the silken cocoons of hymenopteran parasitoids. But if a hole is made in the cocoon, infections occurs (Kaya 1978). Spiracular openings are portals of entry for nematodes (Triggiani and Poinar 1976), but sieve plates over the spiracles, especially with scarab larvae, may deny nematodes access through this entry point (Akhurst 1986). Finally, younger instar of black fly larvae are resistant to infection by Steinernema carposapsae because the comparatively large nematode is excluded from the insect's mouth (Gaugler and Molloy 1981)

physiological- involves the destruction of the nematode by digestive enzymes in the insect's alimentary tract and the melanization and encapsulation of the nematode within the hemocoel. Although there is no example of nematode destruction by digestive enzymes, this probably occurs when a nematode is ingested by a less than suitable host. There are numerous examples of melanization and encapsulation of nematodes within the insect's hemocoel (jackson and Brooks 1989). Encapsulation of filarial nematodes in mosquitoes that serve as intermediate hosts has been known since the early 1900s(Brug 1932). Complete encapsulation of this nematode Steinernema carpocapsae usually occurs within 5 hours after its penetration into the hemocoel of Aedes aegypti (Bronskill 1962). Although the nematode is encapsulated, the majority of the larvae die of septicemia caused by the bacterium Xenorhabdus nematophilus, which is mutualistically associated with this nematode. Surviving mosquito larvae usually die as pupae or shortly after adult emergence. In some cases, the encapsulated nematodes are partially or completely expelled from the host's body cavity at the time of molting.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(466)

Mode of Infection

2008-05-11T22:44:00.000-07:00

Insect-parasitic nematodes parasitize their hosts by directly penetrating through

the cuticle into the hemocoel
by entering through natural openings ( spiracles, mouth, and anus)

Some insect-parasitic nematodes posses a spear or stylet that is used to pierce the cuticle.

e.g-order Tylenchida possess a stylet, and those in the order Mermithida possess a spear, which is technically called an odontostyle.

Some rhabditids can penetrate into the hemocoel, and Heterorhabditis has an anterior tooth that is used to scrape and rupture the host's cuticle.

Nematodes infect their insect hosts

Passive infection- occurs when a mermithid deposits its eggs on the host's food. The eggs are ingested by an insect, and the nematodes hatch, bore through the midgut, and enter the hemocoel. For example: Christie (1937) has described hatching and penetration by Mermis nigrescens through the midgut of a grasshopper. About 2 hour after ingestion, the egg hatches at the posterior end of the midgut near the region where the Malpighian tubules are attached. The infective juvenile uses its spear to penetrate through the midgut into the hemocoel within 20 to 30 min.
Active infection- occurs when the nematodes seek their hosts and penetrate directly through the intergument into the hemocoel. For Example: The penetration process of the sphaerulariid Tripius sciarae into the dipteran host Bradysia paupera. The infective adult female, ensheathed in the fourth-stage cuticle, process an adhesive mass about its head. This secretion digests the anterior portion of the ensheathed cuticle and adheres the nematode to the host. The attached nematode uses its stylet and possibly some enzymes to penetrate into the host. The penetration process may take from 10 min to 2 hours, and the wound is sealed by the adhesive substance after the nematode has entered the insect. In Deladenus siricidicola, no secretions are produced during the penetration process. The infective adult nematode adopts a position for entry with its head at a right angle to the larval wood wasp and then begins to thrust its stylet in and out at the rate of 60 to 100 thrusts per min. Initial penetration of the integument takes from 30 sec to 60 min, and the nematode completely enters its host after 40 to 60 min.

Host finding by infective juveniles of steinenematid and heterorhabditid nematodes can be an active process in response to physical and chemical cues. For example, Steinernema carpocapsae forms aggregations in response to chemical and bacterial gradients (Pye and Burman 1981), host fecal components (Schmidt and All 1978, 1979), plant roots (Bird and Bird 1986), and carbon dioxide (Gaugler et al 1980).

Once a suitable host is found, S. carpocapsae invades by entering the mouth or the anus and then mechanically penetrating through the midgut into the hemocoel (Poinar and Himsworth 1967). It also infects its host y entering through the spiracles in response to carbon dioxide (Gaugler 1991) and penetrating into the hemocoel (Triggiani and Poinar 1976)

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(465-466)

Host Specificity

2008-05-11T21:20:00.000-07:00

Specificity of nematodes can be categorized into three groups

Monoxenous (highly specific or species specific)
Oligoxenous (moderately specific or limited host range)
Polyxenous (little specificity or wide host range)

Nematodes that are obligate parasites of insects tend to be monoxenous or oligoxenous.
for example:The mermithid Perutilimermis culicis appears to be specific to the mosquito Aedes sollicitans (Petersen 1967).

In contrast, some steinernematids and heterorhabditis are polyxenic are polyxenic. For example, Steinernema carpocapsae insects more than 250 species of insects from several different orders under laboratory conditions (Poinar 1979), and studies with Heterorhabditis bacteriophora indicate that it has a broad host range.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(464-465)

Types of Insect-Nematode Associations

2008-05-11T20:28:00.000-07:00

Van Zwaluwenburg (1928)-five classifications:

Primary parasitism
Secondary parasitism
mechanical association (internal)
mechanical association (external)
commensalism

Steinhaus (1949)

nematode parasites of the insect gut
nematode semiparasitic in insects
nematode parasites of the body cavity and tissues of insects.

Poinar's (1975)

phoretic relationship-a form of commensalism in which one organism association with another species in order to obtain transportation, are common between insects and nematodes. These nematodes have little or no pathological effect on the host and benefit by being carried to a new environment.
facultative parasitism- Nematodes are able to infect healthy insects as well as having the ability to complete their life cycle as free-living organisms.
obligate parasitism- Obligate parasites cannot complete their life cycle in nature without a living insect. Nematodes in the families Steinernematidae and Heterorhabditidae are classified as obligate parasites of insects.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(463-464)

General Life Cycle of Nematodes

2008-05-11T20:00:00.000-07:00

Most nematodes have simple life cycles and undergo three main stages of development: egg, juvenile (immature stages of nematodes are called juveniles to avoid confusion with larval stages of insects) and adult.

In a simple life cycle, the mated female deposits her eggs in the environment and the juvenile usually undergoes one molt in the egg and emerges as a second-stage juvenile. The majority of nematode species molt four times before becoming adults. These molts may occur in the egg, free in the environment, or in the insect host.

Some insect nematodes have a resistant stage called the"dauer juvenile" or "dauer." The dauer juvenile is the third-stage nematode, which is usually ensheathed in the second-stage cuticle and commonly in the rhabditis.

Many noninfectious (free-living) nematodes produce dauer juveniles. Immature nematodes are like the adults in appearance and structure, and therefore their development is analogous to ametabolous insects. Most nematodes are amphigous (male and female are separate individuals) and mating is required to produce offspring.

Some entomogenous nematodes have complex life cycles, which include an alternation of gametogenic and parthenogenetic generations

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(461-462)

Taxonnomy of Nematode

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Identification of entomogenous nematodes to species is difficult or not possible with immature stages; the adult stages are often required for proper identification.

The specimens, in properly preserved condition, should be sent to nematode taxonomist.
Special methods are required for killing and fixing insect neamtodes-hot(80 degree C) Ringer's solution or 1 % sodium chloride solution
Preserved in either TAF (7 ml formaldehyde-38%, 2 ml triethanolamine, and 91 ml distilled water).
Ethyl alcohol, a general insect preservative, causes distortion of the internal anatomy of nematodes and is not recommended.

References:
Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC. P(461)

Steinernematidae

2008-05-11T19:34:00.000-07:00

nematode Steinernema glaseri infecting the Japanes Beetle (Popillia japonica)
-significant reduction in beetles populations

Dutch and Hough (1955) found steinernematid known as the DD-136 strain of Steinernema carpocapsae and tested it on the codling moth.

The use of S. glaseri and S.carpocapsae in biological control was accelerated because of the imagination of their discoverers and the ease in producing great numbers of nematodes on an artificial medium or a suitable insect host. These nematodes are currently being applied against agricultural and turf pests.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(460-461)

Nematodes

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Commonly referred to-Roundworms, eelworms, threadworms.

-translucent
-elongate
-less cylindrical throughout their body length.
-the body is covered by a noncellular elastic cuticle
-transverse striae or external annulations often occur on the cuticle
-no true segmentation
-have excretory, nervous, digestive, reproductive, and muscular system
-lack circulatory and respiratory systems.
-the alimentary canal consists of a mouth situated terminally, followed by the stoma or buccal cavity, an esophagus, intestine, and rectum with the anus opening ventrally.

Sexes are usually separate.

-The male's reproductive system opens ventrally into the rectum forming a cloaca.
-The adult male is distinguished by the presence of one or two testes and by spicules in association with the cloaca.
-The female's reproductive system involves one or two ovaries with the vulva located ventrally, usually near the middle of the body.
-The immature nematodes are difficult to sex because there are no apparent genital stucture.

Habitat of nematodes

-Have habitats more varied than any other group of animals.
-There are found from the arid dessert to the frozen tundra, from fresh to salt water, and from hot springs to thawed-out Arctic ice.
-Nematodes occur as free-living organisms and as facultative or obligate parasites(pathogens) of plants and animals.

Insects serve as vectors or intermediate hosts for a number of nematode parasites of vertebrates.For example:

-Mosquitoes transmit Dirofilaria immitis- causal agent of the dog heartworm
-Wuchereria bancrofti-causal agent of filariasis in humans
-Coprophagus beetles serve as intermediate hosts for Spirocerca lupi-tumor-causing nematode in dogs.
-Rhadinaphelenchus cocophilus-causative agent of red0ring disease of coconut palm, is transmitted on part by palm weevils.
Bursaphelenchus xylophilus, causative agent of wilting disease of pine trees.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(459-460)

Sotto Disease

2008-05-11T18:34:00.000-07:00

In 1901, Ishiwata isolated a bacillus from diseasea silkworm larvae. He found the bacillus so highly pathogenic to larval silkworms that he named it"sotto disease bacillus"(sudden-collapse bacillus).

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(87)

Latent, Chronic, and Acute Infections

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Latent infections:

-May occur with various types of pathogens that are present in the insect in a "dormant" or nonactive stage and produce no signs or symptoms.
-Latent infections in insects have been observed primarily with virus.

Termite Nutrition

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The type of food consumed by termites

-Governed by the reducing capacity (redox potential) of the hindgut

e.g Zootermopsis nevadensis, the hindgut has a strong reducing condition for the anaerobic fermentation of wood. Mildly reducing condition occurs in the hindgut of Cubitermes severus

The quantitative analysis of cellulose digestion is complicated

-Metabolic activity of the intestinal bacteria
-the flagellates, when under going cytolysis, release unidentified products into the substrate.

Signs, Symptoms and Syndromes

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Symptom- a functional or behavioral disturbance. It may be expressed by abnormal movement, abnormal response to stimuli, digestive disturbance, inability to mate.

Sign-a physical or structure abnormalities. It may be indicated by abnormalities in the morphology or structure, changes in color, malformation of appendages, integument.

Syndromes-a system complex or a particular combination, set, or sequence of signs and symptoms. At times, the syndrome is very characteristic and specific for a disease caused by a pathogen.

DIAGNOSIS

2008-05-11T00:40:00.000-07:00

Diagnosis is a fundamental branch of insect pathology and should be allotted a similar position of importance as in the case for human, vertebrate, and plant pathologies. In order to accomplish a proper diagnosis, a study has to be made of the etiology, symptomatology, pathogenesis, pathologies, and epizootiology of the disease. Thus, diagnosis is one of the most complex branches of insect pathology.

There are various types of diagnostic operations, such as symptomatic diagnosis, laboratory diagnosis, postmortem diagnosis.

Differential diagnosis compares and contrasts the signs and symptoms and postmortem changes of different diseases in a systematic manner to distinguish one disease from another.

Preliminary diagnosis is the first cursory examination of a diseased insect. It is generally an educated guess of the type and cause of disease.

Tentative diagnosis is made after general an educated macroscopic and microscopic examinations have been conducted on a disease specimen. It often involves routine laboratory tests.

Definitive diagnosis completes the diagnosis, and a final conclusion is reached after all pertinent data and facts have been gathered, tabulated, analyzed, and adjusted.The conclusion is based on information derived from the laboratory, field, and literature.

In diagnosis, two procedures:

Collection of facts and data
Analysis of these facts and data

The facts and Data;

History of disease
Physical examination

General inspection
Macroscopic examination
Microscopic examination

3. Laboratory and ancillary examinations

Isolation and possible study of microbial pathogens
Assay for nonmicrobial factors (e.g -poison, metabolic diseases)
Detailed study of host; biochemical and biophysical tests of tissues and fluids
Observation of course of disease

Portal of Entry

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The portal of entry are the points or sites through which a pathogen invades or gains entrance into an insect. Invasion may take place through the integument which may be intact or broken by injury, by the way of the and mouth and digestive tract, by congenital passage through the ova and spermatozoa, through the anus,and through the spiracles and other body openings. Parasitic insects an other vectors may also transmit the pathogen into a susceptible host insect. Passage through the intergument and mouth are the most common portals of entry. unlike humans and other vertebrates where respiratory tract infections are common occurrence, the spiracles and trachae of insects are rarely invaded by pathogens.

The method of entry varies with the type of pathogen. Fungi and nematodes generally invade through the intergument, whereas viruses, bacteria and protozoa enter their host primarily through the mouth. There are more cases of congenital transmission with viruses and protozoa than with other pathogens. Such congenital transmission most frequently occurs by way of the egg, either through the ovary (transovarial transmission) or on the surface of the egg (transovum transmission). The term "transovum transmission" is used to refer to passage of a pathogen on or within the egg. A special case of transovum transmission is transovarial transmission in which the pathogen enters the egg while it is still in the ovary. There are only a few reported cases of transmission by the way of the male (venereal transmission in insects)The sigma virus of Drosophilia melanogaster is usually transmitted through the egg, but it can also passed to the progeny via sperm. The microsporidia Nosema fumiferanae and N.plodiae are transmitted to their offspring by adult males of the spruce budworm, Choristoneura fumiferana, and of the Indianmeal moth, Plodia interpunctella, respectively.

Microbial Diseases

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In microbial disease, pathogenic microorganisms generally invade and multiply in an insect and spread to infect other insect. Pathogens are transmitted to insects by contact, ingestion, and vectors, and form the parents to their offspring. The pathogens are noncellular, parasitic infectious agents (viruses), prokryotic forms (organisms with a true nucleus and nuclear membrane, such as bacteria), and eukaryotic forms (organisms with a true nucleus enclosed by a nuclear membrane, such as fungi and protozoan). In addition, we have included the nematodes even though they are often larger and more complex than microorganisms. Nematodes have characteristics of both parasitoids-predators an microbial pathogens, but they are placed with pathogens because they have no functional response and often produce pathologies similar to pathogens.

The term parasite has been used, at times, interchangeably or synonymously with pathogen. We restrict the use of the terms parasite and parasitoid to the larger and more complex organism that generally does not multiply on or in the insect. These are exceptions. Polyembryonic parasitoids lay a single egg in an insect host and the egg subsequently divides to produce from a few to several hundred embryos. The mite Acarapis woodi, causal agents of the Isle of Wight disease in the honey bee, enters the adult bee through the trachea and injure the surrounding muscle and nerve tissues (Anderson 1928). On the other hand, some gregarines (protozoa) do not multiply when they enter their insect insect host. Their multiplication occurs in a stage outside of the host. Thus, there is some overlapping in the definitions of parasite and pathogen, but in general, the pathogens are minute and multiply on or in the host. For nematodes, some (e-.g mermithids) are referred to as parasites; whereas others (e.g: steinernematids) are referred to as pathogens.

A successful infection of an insect by a microorganism depends on the properties and characteristics possessed by both organisms. Since the pathogenic properties of the microorganism are pitted against the resistive properties of the host, the basis for infection, at times, is difficult to determine whether it is due to the properties of the pathogen or those of the host.

Flagellates

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The mutualistic protozoa in the lower termite and the wood-eating termite coackroach are unique flagellates that are restricted to these hosts. They are oxymonad, trichomonad and hypermastigote flagellates.

Protozoa have not evolved as rapidly as the speciation that has occurred in termites, and seems probable that many flagellates known today may have existed in ancestors of the termites (Kirby 1937,1949). The close similarity between the protozoan faunale in the lower termites and in the wood-eating cockroach is one of the bases for the proposal that termite and the cockroach evolved from a preblattid ancestor.

Certain flagellates are restricted to a single species or species complex of termites, and workers have suggested their use in diagnosing or identifying species, especially those of lower termites, and in some cases of higher termites. The presence of internal flagellates appears to have induced a rather high rate of race-forming process in the termites.

Location in Termite

In the termite, the bulk of the microbiota including the protozoans is confined to the thin-walled enlarged hindgut, which unlike that of most insects, plays the major role in the absorption of nutients (Breznak 1984). Absorption also occurs in the midgut, but this is limited to soluble nutrients present in food or those liberated from food by termites-secreted enzymes or by bacteria that may colonize the midgut.

Termite castes may harbor the same species of flagellates, although the workers, nymphs, and alates may have larger number of flagellates than the soldier(Lai et al.1984). In some termites, each flagellates species occupies a more or less distinct location in the hindgut of the worker. This suggests that different flagellate species have specific roles in termite nutrition and some are more directly involved than others in the breakdown of cellulose.

Reinfestation

The protozoan are absent in newly hatched termite nymphs. Most or all of the protozoa are lost at times of molting, except in the last molt to adults, and are not found in certain of the reproductive castes (Cleveland 1925). Termite nymphs have to reinfested with protozoan in order to survive. The reinfestation is accomplished by feeding on the exudates from the anus of infested individuals (Proctodaeal feeding) and by accepting food from nursing workers (stomodaeal feeding).

Internal Microbiota of Termites

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The rich protozoan faunule of termites may have been first noticed by Lespes in 1856 when he observed that the intestines were ordinarily filled with a living agglomeration of infusorians. The protozoan biomass in the termite during the intermolt period may consist of one-seventh to one-third of the body weight of the termite. When students in insect pathology examine a fecal droplet of a worker termite in a wet mount, they are fascinated by the vast milieu of animalculi in constant motion. Most of the microorganisms are flagellates and bacteria.

Mutualistic bacteria and unique protozoa are found mainly in the five families of lower termite: Mastotermitidae, Hodotermitidae, Kalotermitidae, Rhinotermitidae, and Serritermitidae (Breznak 1982). They are absent or rare in the higher family Termitidae; those that are found appear not to be associated mutualistically with these termites. The wood-eating cockroach Cryptocercus punctulatus has a protozoan faunule similar to that of the lower termites.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.

Potrikus, C. J., and J. A. Breznak. 1980. Uric acid in wood-eating termites. Insect Biochemistry 10 (1):19-27.

Bacteria in Insects

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The most common bacterial flora found in digestive tracts of healthy insects are gram-negative small rods and, in this respects, resemble the flora of higher animals. Colliform bacteria are frequently found followed by micrococci and spore-forming bacilli. Spirilli are rarely found in the normal insect's gut with the exception of certain termites. Many of these bacteria are saprophytes and occur ubiquitously in nature; others are obligate anaerobes that are specific to insect. Specialized appendages, such as "gastric caeca," attached to the gut may be filled with a large number of bacteria that are characteristic for the insect species harboring them. These cases are found especially in the higher Hemiptera.

The bacteria, in different insect species, may range from very small to rods to large spirochete-like forms, and they are difficult to culture on artificial media. Some of these bacteria are intimately attached to the midgut epithelium and chitinous wall of the hindgut. Adult insects pass some bacteria from generation to generation in association with the egg. The bacteria appear to play a mutualistic role with the insect host by providing the host with nutrients and other substances and obtaining in return a home and means of transmission.

Bacteria of the internal microbiota may favor the insect host by serving as food, assisting in the digestion of food, producing enzymes, synthesizing vitamins, fixing nitrogen, producing pheromones, and preventing contamination of the insect's mid-gut by other microorganism. We have already touched upon these areas except in the case of nitrogen fixation. We shall expand on pheromone production.

Certain bacteria in the guts of termites are capable of fixing atmospheric nitrogen. The following nitrogen-fixing bacteria have been isolated: Citrobacter freundii from Coptotermes lacteus, Mastotermes darwiniensis, and Nasutitermes exitious and Enterobacter agglomerans from Coptotermes formosanus.

These bacteria may be important in the nitrogen economy of the termite. Prior to discovery of the nitrogen-fixing bacteria, the general belief was that nitrogen is conserved in termites by recycling the nitrogen in cadavers of dead protozoa and other dead microbiota, and by the termites feeding on dead termites.

Uricolytic bacteria, Stretococcus sp., Bacteroides termitidis, and Citrobacter sp., are found in the termite Reticulitermes flavipes (Potrikus and Breznak 1980). These bacteria can convert uric acid under the anaerobic condition of the digestive tract into products usable by termite for carbon,nitrogen, energy, or all three. However, the importance of the nitrogen-fixing bacteria in termite nutrition is still to be established. For example, Nazarczuk et al.(1981) have observed that the gut flora and fauna of Nasutitermes exitious and Coptotermes lacteus may not fix nitrogen under short-term conditions.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.

Roslyn A. Nazarczuk, R. W. O'Brien, and M. Slaytor. 1981. Alteration of the gut microbiota and its effect on nitrogen metabolism in termites. Insect Biochemistry 11 (3):267-275.

Potrikus, C. J., and J. A. Breznak. 1980. Uric acid in wood-eating termites. Insect Biochemistry 10 (1):19-27.

Internal Microbiota

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Internal microbiota of insects are found in the lumens of the trachea and the digestive tract; in cavities, pouches, ducts, etc.; in the hemocoel (intrahemocoelic); and within cells (intracellular). They are generally greater in numbers and more varied in types than the external microbiota.

As in the case of the external microbiota, the environment of the insects plays an important role in determining the quality and quantity of the internal microbioata. The microoraganism in the digestive tract are generally bacteria or bacteria-like organisms and occasionally yeasts. The anatomy of an insect may also govern the types and quantities of microorganisms.

Some insects(e.g-Termites and cockroaches) depend on the enzymes produced by the internal microbiota for the digestion of food, and others obtain such enymes from the ingested external microbiota as in the case of fungus-growing ants.

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(22)

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Termites

Termites from the third largest group of insects that cultivate fungi for food, but not all termites cultivate fungi. Those that do belong to the family Termitidae (Higher termites)(Wood and Thomas 1989).They usually live in a large nests (termitaria), which are built above or below ground. The termitarium contains special chambers in which the fungus is cultivated on "fungus combs" that are derived from termite fecal material. The surfaces of the combs are covered sparsely by fungal mycellium, spherical or nodulelike conidia, and conidiophores. The mycelia permeate the entire comband may help in maintaining the required humidity within the nest(Zoberi 1979). The fungal combs have high nutrional value (Rohrmann 1978), and termite cannot survive without the combs (Sands 1969).

Some termite species seem to have their own species of fungus. The fungal genus commonly associated with termites is Termitomyces (Basidiomycotina) (Wood and Thomas 1989). The fungus is carried by the female or male alate which ingests the asexual spores and carries them as a bolus in its digestive tract. The spores pass through the digestive tract and inoculate the fecal deposits of foraging workers.

Higher termite, unlike lower termites, don't rely on mutualistic protozoans for the production of digestive enzymes. The adult workers (Subfamily-Macrotermitinae) produce, in their midgut epithelium and salivary glands, digestive enzymes to digest cellulose (Wood and Thomas 1989). Bacteria in the digestive tract of the termite may produce digestive enzymes. The cellulases are produced also by the fungus and are acquired by termites feeding on the fungal combs.

A mutualistic association occurs between the fungus Termitomyces and the termite by providing the termite with digestive enzymes and nourishment and the termite maintains the fungal garden free of invaders (Wood and Thomas 1989). Termitomyces has no active existence outside of the fungal combs

References:

Yoshinori Tanada, Harry K. Kaya. 1993. Insect Pathology: ACADEMIC PRESS, INC.P(21)

The Father of Insect Pathology

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The nineteenth century was the renaissance for insect pathology. In the mid-1830s, Agostino Bassi, the father of insect pathology, demonstrated that a microorganism (fungus) cause disease in animal (silkworm).