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 Russian wheat aphid, Diuraphis noxia, and its common parasitoid, Aphelinus asychis, were investigated under laboratory conditions to determine if fungal infection of the aphid host had an effect on oviposition and feeding behavior 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 third instars (5.2 X 10(4) conidia/cm(2)). At various intervals afterward they were exposed to 4- to 5-day-old mated parasitoid females for I h. Various combinations of treatments were examined: exposure to P. fumosoroseus and parasitization simultaneously; exposure to parasitoids 24-96 h after treatment with fungus; exposure to the parasitoid alone; and fungal treatment alone. The average number of aphids probed by the parasitoids was not significantly influenced by host infection with P. fumosoroseus, but duration of ovipositor insertion was influenced by the length of the time interval between exposure to P. fumosoroseus and subsequent exposure to the parasitoid. Parasitoid females spent considerably less time with their ovipositor inserted 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 upon by parasitoids was significantly less than in the other treatment groups. The percentage of successfully parasitized D. noxia was significantly reduced as a function of the time between treatment with P. fumosoroseus and parasitoid oviposition. The effect of previous parasitization on the ability of the fungus to infect aphids and interfere with parasitoid development within host aphids was also investigated. The number of mummies produced by two female A. asychis during 24 h of exposure varied from 20.3 to 23.0 and was not significantly different when the aphids were first exposed to the parasitoids 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 untreated groups was noted, but the percentage of emergence of the F1 generation of A. asychis was significantly lower among the aphids exposed to the parasitoid and treated with the fungus 24 h afterward than for the untreated aphids. Various findings of this study demonstrate the potential of synergistic interaction of P. fumosoroseus and A asychis for the biological control of D. noxia.