Individual and combined effects of the fungus, <i>Paecilomyces fumosoroseus</i> and parasitoid, <i>Aphelinus asychis</i> Walker (Hym., Aphelinidae) on confined populations of Russian wheat aphid, <i>Diuraphis noxia</i> (Mordvilko) (Hom., Aphididae) under field conditions

Abstract 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, Paecilomyces fumosoroseus , were evaluated separately and in combination against confined populations of D. noxia under field conditions. Groups of 10 infested barley plants were treated in a spray tower with either 10 ml of a fungal suspension (1.7 × 10 7 conidia/ml) [with and without incubation for 24 h under ideal conditions ( Pfr; Pfr (24 h), respectively)] or four female A. asychis ( Aa ) or both fungus and parasitoids ( Pfr + Aa ). Insects treated with Pfr + Aa or Aa responded with higher mortality at 7 and 10 days post‐treatment than controls or those receiving only the fungus. Laboratory studies confirmed mycosis in cadavers of D. noxia that were recovered from plants that had received fungal treatments 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 in 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 of the test 13 days post‐treatment, the density of aphids on plants treated 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 differences in the percentages of aphid age groups were observed between treatments involving A. asychis and all other treatments and controls 13 days post‐treatment; there was a significant reduction of the percentage 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‐treatment. These studies reveal an additive effect of P. fumosoroseus and A. asychis with regard to aphid control with no detrimental effects on the percentage of parasitism nor parasitoid emergence when the two agents were used together.