Interactions among the entomopathogenic fungus, Paecilomyces fumosoroseus (Deuteromycotina : Hyphomycetes), the parasitoid, Aphelinus asychis (Hymenoptera : Aphelinidae), and their aphid host

The interactions among the hyphomycete, Paecilomyces fumosoroseus, the Russ ian wheat aphid, Diuraphis noxia, and its common parasitoid, Aphelinus asyc his, were investigated under laboratory conditions to determine if fungal i nfection of the aphid host had an effect on oviposition and feeding behavio r of the female parasitoid and on development of parasitoid progeny. Aphids were first treated with 2 times the LD95 of P. fumosoroseus for D. noxia t hird instars (5.2 X 10(4) conidia/cm(2)). At various intervals afterward th ey were exposed to 4- to 5-day-old mated parasitoid females for I h. Variou s combinations of treatments were examined: exposure to P. fumosoroseus and parasitization simultaneously; exposure to parasitoids 24-96 h after treat ment with fungus; exposure to the parasitoid alone; and fungal treatment al one. The average number of aphids probed by the parasitoids was not signifi cantly influenced by host infection with P. fumosoroseus, but duration of o vipositor insertion was influenced by the length of the time interval betwe en exposure to P. fumosoroseus and subsequent exposure to the parasitoid. P arasitoid females spent considerably less time with their ovipositor insert ed in dead aphids and in aphids that had been exposed to P. fumosoroseus 72 h prior to contact with the parasitoids. The number of dead aphids fed upo n by parasitoids was significantly less than in the other treatment groups. The percentage of successfully parasitized D. noxia was significantly redu ced as a function of the time between treatment with P. fumosoroseus and pa rasitoid oviposition. The effect of previous parasitization on the ability of the fungus to infect aphids and interfere with parasitoid development wi thin host aphids was also investigated. The number of mummies produced by t wo female A. asychis during 24 h of exposure varied from 20.3 to 23.0 and w as not significantly different when the aphids were first exposed to the pa rasitoids and then treated with P. fumosoroseus 24, 48, 72, and 96 h after exposure. No difference in time between oviposition and emergence of the F1 generation, of the parasitoid for groups treated with the fungus and the u ntreated groups was noted, but the percentage of emergence of the F1 genera tion of A. asychis was significantly lower among the aphids exposed to the parasitoid and treated with the fungus 24 h afterward than for the untreate d aphids. Various findings of this study demonstrate the potential of syner gistic interaction of P. fumosoroseus and A asychis for the biological cont rol of D. noxia.