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Developing a Biocompatible Management Strategy for Onion Maggot Flies 2007

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Project Leaders: B. Nault, J. Nyrop, Dept. of Entomology, NYSAES-Geneva

Cooperators: C. Hoepting, Cornell Cooperative Extension – Albion; S. Wright, USDA-ARS, Kearneysville, WV; C. MacNeil, Cornell Cooperative Extension - Canandaigua

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 a low concentration of the insecticide active ingredient spinosad (<1.0%) plus sucrose.  Spheres were hung about 18 inches from the ground and placed along onion field edges.  We estimated that 45 to 60% of the flies that visited a sphere were killed.  Based on fly visitation rates, we also predicted that one spinosad-baited sphere would kill approximately 182 flies (147 males and 36 females) during the onion-growing season.  In 2007, we wanted to evaluate the performance of these spheres by assessing the level of protection they would provide to onion plants in commercial fields.  Unfortunately, we did not observe a reduction in onion plant damage in field plots of onions where spinosad-baited spheres were placed.  Examination of these spheres in the lab revealed that they failed to kill flies.  Some of these spheres were rinsed with water and scrubbed lightly and the trial was repeated.  This time, 56 to 72% of flies confined within cages containing the “recharged” spinosad-baited spheres died within 72 hrs.  Therefore, it is likely that the poor field performance of the spinosad-baited spheres for protecting the onion crop was due to a problem with the spheres not making the spinosad available.  We believe that extremely dry weather was responsible for this phenomenon.  Additional research is being discussed for dealing with this trap design issue under dry conditions.