Mechanisms of Orientation Disruption by Sex Pheromone Components in the Redbacked Cutworm, Euxoa ochrogaster (Guenée) (Lepidoptera: Noctuidae)

Abstract

Disruption of orientation of Euxoa ochrogaster (Guenee) males to synthetic bait was studied in a flight tunnel and in small field plots, using synthetic pheromone components as disruptants. Field tests showed that increasing the dose from 0 to 100 μg per dispenser of the blend of all four components (Z5-12:Ac + Z7-12:Ac + Z5-10:Ac + Z9-12:Ac) or that of Z5-12:Ac and Z7-12:Ac, individually, resulted in a sharp increase in disruption up to a maximum of 75%; a further increase in the dose to 1,000 μg per dispenser resulted in only a small and gradual increase in disruption, reaching a maximum of 88%. Z5-10:Ac caused approximately 78% disruption at levels of 100 μg and 1,000 μg per dispenser, and Z9-12:Ac was least effective at these doses. Flight tunnel and field observations showed that with blends, the mechanisms of disruption varied in relation to the concentrations used. The primary cause of disruption was competitive attraction at low dose levels and reduction in searching effort at high dose levels. With single components, irrespective of concentrations used, the cause of disruption was primarily reduction in searching effort. Based on these studies and those on Euxoa messoria (Harris) and Malacosoma disstria (Hubner), it is suggested that in moths, depending upon the species, functional nature of the pheromone components, concentrations used, and the method of disruptant dispenser placements, individual or blends of components can cause orientation disruption by competitive attraction and by modulating the behavior of males, particularly by reducing the searching effort.