Moulting

Once feeding commences the nematode can continue development. The majority of nematodes have four juvenile stages before development to the adult; thus, there are four moults where the old cuticle is replaced by a new cuticle. Exceptions include certain species of Xiphinema, which have only three moults and three juvenile stages. During the moulting process the cuticle is either shed completely or, as in Meloidogyne, is partially absorbed. Unlike insects, the nematodes increase in size between moults and not during the moulting process.

Moulting may be a putative control target. Soriano et al. (2004) examined the effects of the ecdysteroid 20-hydroxyecdysone (20E), a major moulting hormone of insects, on M. javanica. Exogenous application of 20E resulted in immobility and death of J2, and invasion was partially inhibited and development was halted in spinach with induced high levels of endogenous 20E; however, of the few J2 that invaded, no abnormal moulting was observed. The biosynthesis of ecdysteroids by any nematode has yet to be demonstrated, and specific efforts to detect 20E and its precursor, ecdysone, in M. arenaria and M. incognita were unsuccessful (Chitwood et al. 1987). The complete sequences of the genomes of M. hapla (Opperman et al. 2008) and M. incognita (Abad et al. 2008) will provide information about the genes involved in moulting in Meloidogyne, and this, together with data from genome projects on other species of nematodes, may provide the basis for a realistic assessment of inhibiting or disrupting moulting as a control strategy.

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