Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2000
Publication Date: N/A
Interpretive Summary: The Russian wheat aphid (RWA) is a worldwide pest of wheat and barley. It was first found in the United States in the mid-1980s. Since then, it has caused a combined direct and indirect economic impact in excess of $1 billion. Two fungi, Beauveria bassiana and Paecilomyces fumosoroseus, have potential as a safe and effective biological control agents for this aphid, ,but field trials are needed to demonstrate their effectiveness. Beauveria bassiana is registered and labeled as a pesticide for control of aphids and other insects. In studies over 4 seasons, we applied both fungi to small plots using a backpack sprayer and we applied B. bassiana to larger plots using an overhead irrigation system. We found that Beauveria bassiana application reduced aphid numbers in each year. Application of Paecilomyces reduced aphid populations in one of two years tested. We showed that up to 83% of treated aphids can become infected with fungi under optimal conditions. We also documented that viable spores persist o wheat leaves more than 5 days after application, but at numbers too low to have an impact on aphids. These studies demonstrate the potential for control of Russian wheat aphid using fungi and illustrate a feasible large-scale application scheme.
Technical Abstract: Field plots of irrigated spring and winter wheat in southeastern Idaho, USA, were infested with Russian wheat aphid, Diuraphis noxia, and later treated with either Beauveria bassiana or Paecilomyces fumosoroseus at rates of 2.5 or 5 x 1013 spores/ha. Small plots (1.4 to 6.6 m2) were treated with a backpack sprayer in 1995-1998 and large plots (470 m2) were treated using an overhead irrigation system in 1997 and 1998. Significant reductions in aphid populations were observed following some, but not all, fungus treatments in small-plot experiments in spring wheat 3 years (1995 - 1997) but not in winter wheat (1998). Significant reductions in both aphid densities and the percentage of tiller infestation were observed in large-plot experiments in both spring (1997) and winter wheat (1998). Fungus-treated aphids suffered 32 to 83% mycosis when field-treated tillers were incubated in the laboratory. Persistence of fungal inocula of either species, measured by estimating CFUs obtained from washed leaf segments, dropped by 10- to 1000-fold within 3 to 5 days. These studies demonstrate the potential for control of Russian wheat aphid using fungi and illustrate a feasible large-scale application scheme.