Mermithid parasites of agricultural pest insects.

T h i s pape r assesses ou r state of knowledge of physiological processes involved in the re la t ionships between insects and the i r m e r m i t h i d ne m a tode parasi tes. T h r e e ma jo r componen t s of the host -paras i te relat ionship(s) are reviewed: effects of m e r m i t h i d s on hos t physiology, effects of hos t physiology on mermi th id s , and the physiology of the nema todes themselves. Mermi th id s induce an array of changes in host physiology, and the effects on hos t me tabo l i sm and endocrinology are discussed at some length . Few studies have been done to ascertain the effects of the hos t on the parasi tes f rom a physiological s t andpo in t . Whereas hos t i m m u n i t y mechan i sms agains t m e r m i t h i d s have been described at the u l t r a s t ruc tu ra l level, the physiological basis of such responses is no t known. Mermi th id s are atypical nematodes , bo th s t ruc tura l ly a n d physiologically. In the absence of a func t iona l gut , nu t r i en t s are absorbed across the ou te r cuticle and stored in a t rophosome. T h e t ranscu t icu la r m ode of feeding, s torage wi th in the t rophosome, and me tabo l i sm of s torage p roduc t s are discussed. T h e usefulness of physiological i n fo rma t ion toward exped i t ing in vitro cu l tu re of these nema todes is discussed, and p rob lems tha t need to be addressed are defined.