Histopathology of an aphid, Schoutedenia lutea, parasitized by a gall midge, Pseudendaphis sp

Pseudendaphis sp. (Barnes) [Diptera: Cecidomyiidae] is a larval endoparasitoid of the aphid Schoutedenia lutea (van der Goot) [Aphididae: Greenideinae]. A brief investigation of the biology of Pseudendaphis sp. revealed that parasitization by this species occurs only in viviparous instar III to adult life stages of the host aphid. Comparative histology of parasitized, unparasitized and starved aphids was used to evaluate proposed mechanisms of pathogenesis. Parasitization by Pseudendaphis sp. was found to cause the destruction of host embryos and pathological changes in the host fat body, yet resulted in an increase in the number of host mycetocytes. There was no evidence of injury to host tissues through direct physical attack, a cytolytic enzyme or starvation-like factors. Remaining hypotheses for altered host histologies in parasitized aphids are selective nutrient depletion and production of a non-cytolytic bioactive substance by the Pseudendaphis larvae.