Exploring lethal and sublethal effects of conventional insecticides and insect growth regulators on a picture-winged fly (Diptera: Ulidiidae) pest of sweet corn

Abstract

Picture-winged flies (Diptera: Ulidiidae) known as corn silk flies are intensively managed with pyrethroids in fresh market sweet corn, Zea mays L., grown in Florida. The identification of alternatives to pyrethroids is needed to increase the efficacy of insecticidal management and to allow the rotation of modes of action for insecticide resistance management (IRM). This laboratory study determined the lethal and sublethal effects of six pyrethroids, five neonicotinoids, four insect growth regulators, two diamides, one spinosyn, one avermectin, and one oxadiazine on adults of the corn silk fly, Euxesta eluta Loew, following topical or ingestion exposure. For topical exposure, pyrethroids caused the highest mortality (≥89%), followed by spinetoram (50%), whereas the remaining insecticides caused <15% mortality. For ingestion exposure, spinetoram caused 95% mortality, followed by dinotefuran, clothianidin, and thiamethoxam, which caused ≥74% mortality. The further evaluation of insecticides causing <15% mortality showed that topical exposure to abamectin reduced by 61.5% the fertility of E. eluta females expressed as the number of larvae per cumulative female-day. None of the insecticides causing <15% mortality following ingestion exposure affected E. eluta fertility. This study confirms that pyrethroids represent the main commercial insecticide option for effective foliar applications targeting adult corn silk flies. Potential alternatives to pyrethroids were highly effective only through ingestion exposure, suggesting the need for the development of management tactics promoting ingestion of insecticides. This study complements pyrethroid susceptibility monitoring for the development of an IRM program in Florida sweet corn.