Insecticide bioassays against Florida’s most destructive sweet corn pests

Silk flies (Euxesta and Chaetopsis spp., Diptera: Ulidiidae) species are among the most severe sweet corn pests in Florida.   These flies are highly damaging to fresh market sweet corn and are the targets of numerous broad spectrum insecticidal sprays during sweet corn’s reproductive stages.  In recent years, scouts have commented that the flies are becoming more difficult to control.  Other older products are now heavily restricted, leading to a heavy reliance on pyrethroids.  Laboratory bioassays were performed during 2012-2014 to determine whether or not there were susceptibility differences to commercially-used insecticides among C. massyla, E. eluta, and E. stigmatias.  Results indicate that E. stigmatias is more tolerant to several pyrethroids than the other two tested species.  In an additional experiment, the E. stigmatias LC₅₀ to beta-cyfluthrin was higher than a label spray rate concentration under the experimental conditions used, and higher than the other species tested.  This tolerance can be countered with the addition of the synergist piperonyl butoxide, indicating metabolic pyrethroid degradation.