INDIVIDUAL AND COMBINED EFFECTS OF THE FUNGUS, PAECILOMYCES-FUMOSOROSEUS AND PARASITOID, APHELINUS-ASYCHIS WALKER (HYM, APHELINIDAE) ON CONFINED POPULATIONS OF RUSSIAN WHEAT APHID, DIURAPHIS-NOXIA (MORDVILKO) (HOM, APHIDIDAE) UNDER FIELD CONDITIONS

The natural enemies of Diuraphis noxia (Russian wheat aphid) can play an important role in the dynamics of aphid populations. The aphelinid wasp parasite, Aphelinus asychis, and the hyphomycete fungus, Paecilom yces fumosoroseus, were evaluated separately and in combination agains t confined populations of D. noxia under field conditions. Groups of 1 0 infested barley plants were treated in a spray tower with either 10 mi of a fungal suspension (1.7 x 10(7) conidia/ml) [with and without i ncubation for 24 h under ideal conditions (Pfr; Pfr (24 h), respective ly)] or four female A. asychis (Aa) or both fungus and parasitoids (Pf r + Aa). Insects treated with Pfr + Aa or Aa responded with higher mor tality at 7 and 10 days post-treatment than controls or those receivin g only the fungus. Laboratory studies confirmed mycosis in cadavers of D. noxia that were recovered from plants that had received fungal tre atments ranged from 24.4 to 31.9% (Pfr); 26.6 to 43.3% (Pfr(24 h)) and 27.7 to 34.5% (Pfr + Aa). The total number of living aphids per plant was significantly lower in the treatments involving A. asychis than i n all other treatments and controls throughout the test. Significantly lower numbers of D. noxia relative to controls were also observed 13 days post-treatment for the Pfr (24 h) treatment. At the termination o f the test 13 days post-treatment, the density of aphids on plants tre ated with Pfr Aa, Aa, Pfr(24 h) and Pfr was 38.2%, 43.1%, 70.5% and 91 .9% of that observed on control plants, respectively. Significant diff erences in the percentages of aphid age groups were observed between t reatments involving A. asychis and all other treatments and controls 1 3 days post-treatment; there was a significant reduction of the percen tage of younger instar and relative increase in older instars for the treatments involving A. asychis. The dry weight of plants treated with Pfr + Aa was significantly greater than controls 13 days post-treatme nt. These studies reveal an additive effect of P. fumosoroseus and A. asychis with regard to aphid control with no detrimental effects on th e percentage of parasitism nor parasitoid emergence when the two agent s were used together.