Submitted to: Journal of Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/1999
Publication Date: N/A
Citation: Interpretive Summary: The Russian wheat aphid is a worldwide pest of wheat and barley. It was first found in the United States in the mid-1980s and has since had a combined direct and indirect economic impact in excess of $1 billion. Cumulative yield losses exceeded 106 million bushels by 1993, and over 20% of small grain acreage in 16 western states was infested. Alarm pheromones sare volatile chemicals produced by some aphids in response to disturbance. Their effect is to stimulate movement by nearby aphids and this response may help aphids avoid predators. For this study we determined if Russian wheat aphid is capable of producing or responding to alarm pheromone. We also tested whether combined application of alarm pheromone and an aphid-pathogenic fungus would lead to elevated infection rates, since increased aphid movement may increase exposure to fungal spores. In the first experiment, Russian wheat aphids responded to pheromones produced by nearby injured aphids by exiting a test arena much more quickly than aphids placed near an uninjured aphid. In a test with synthetic alarm pheromone, we found that aphids respond to increasing concentrations of pheromones by exiting test arenas more quickly. However, we found no added effect of combining pheromone with an aphid-pathogenic fungus. This is the first report that the Russian wheat aphid responds to alarm pheromone and the first evidence that it may produce pheromone.
Technical Abstract: In a series of laboratory tests, Russian wheat aphids, Diuraphis noxia (Mordvilko), responded to synthetic aphid alarm pheromone, (E)-B-farnesene. Late-instar nymphs and adult D. noxia were more responsive to synthetic pheromone than early-instar nymphs. In dose-response assays, EC50 estimates ranged from 0.94 to 8.95 mg per milliliter among three experiments. In arena tests, D. noxia also responded to the proximity of cornicle-damaged nymphs of the green peach aphid, Myzus persicae (Sulzer), or D. noxia, indicating the likelihood of endogenous production of alarm pheromone by D. noxia. This is the first report of the response to, and possible production of, alarm pheromone by D. noxia. Combinations of (E)-B-farnesene and the aphid-pathogenic fungus Paecilomyces fumosoroseus (Wize) Brown and Smith did not enhance mortality of aphids compared with controls treated with fungus only. Further studies involving appropriate formulations of (E)-B-farnesene are necessary before practical biorational strategies can be devised combining this semiochemical and biological control agents.