Sunday, May 11, 2008

General Life Cycle of Nematodes

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)

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