Relationships between the parasitoid Hyposoter exiguae and Trichoplusia ni: Parasitoid-induced histo- and cytopathology

The histology and cytology of Trichoplusia ni larvae were studied for evidence of abnormality or pathology induced by the solitary ichneumonid endoparasitoid, Hyposoter exiguae. Sample control and parasitized larvae were fixed every other day, and sections of these larvae were stained with mercuric-bromophenol blue. The fat body of parasitized larvae failed to show many of the changes characteristic of normally developing controls and, on the last day of parasitism, revealed extensive pathological changes. Spermatogenesis continued normally until the end of the association in parasitized hosts even though their development was halted in the fifth larval stadium. Parasitoid larvae seemed to secrete a proteinaceous material from their salivary and rectal glands into the host hemocoel. This material may be responsible for the pathological changes reported here. The parasitoids apparently fed on hemolymph alone until about 24 hr before emergence and pupation.