Developing a Biocompatible Management Strategy for Onion Maggot Flies

Abstract

The current goal of our research is to develop a biocompatible management strategy for onion maggot flies that would replace the use of foliar applications of broad-spectrum pesticides. Foliar sprays are used in an attempt to kill onion maggot flies before they lay eggs in onion fields. However, there is no evidence that this strategy is worthwhile and there are multiple disadvantages. As an alternative, insecticide-baited devices could be used in onion fields to “attract and kill” onion maggot flies. In 2006, we evaluated the efficacy of spinosad-baited spheres in a commercial onion production area near Elba, NY. These spheres, which were nearly the same size and color as a softball, contained either 0.5 to 1.0% concentration of the insecticide active ingredient spinosad plus sugar. Spheres were hung about 18 inches from the ground and placed along onion field edges for either 1, 2, 3 or 4 months. Because spinosad does not kill flies quickly, mortality of flies encountering the spheres had to be estimated. Spheres were removed from the field and taken to the laboratory and placed singly into cages. Twenty onion maggot flies (1:1 sex ratio) were released into each cage and mortality was recorded over 72 hr. Fly mortality was not affected by the concentration of spinosad, indicating that the lower concentration is sufficient for these devices. Similarly, mortality of female flies was not affected by the duration that the spheres were hung in the field (range in mortality: 45 to 60%). In contrast, mortality of males tended to decline as the duration of spheres hung in the field increased (64% down to 50%). Overall mortality of males and females over the course of the season averaged 55%. We also predicted that one spinosad-baited sphere would kill approximately 182 flies (147 males and 36 females) during the onion-growing season. Onion growers are keenly interested in this tactic because onion maggot is becoming more difficult to control and this tactic will be safe and easily integrated into existing management practices.