Direct and indirect effects of pesticides and pesticide mixtures on the insidious flower bug, Orius insidiosus, under laboratory conditions

Abstract: Western flower thrips (Frankliniella occidentalis) is a major insect pest of greenhouse-grown horticultural crops. Due to the wide-spread incidence of insecticide resistance, greenhouse producers are interested in integrating natural enemies along with insecticides to suppress western flower thrips populations, which may reduce the development of insecticide resistance. One commercially-available biological control agent or natural enemy of the western flower thrips is the insidious flower bug, Orius insidiosus. We conducted a series of laboratory experiments to determine the direct and indirect effects of 28 pesticides and 4 pesticide mixtures (32 total treatments plus a water control) used in greenhouse production systems on adult O. insidiosus survival and predation on western flower thrips adults. A 1.0 ml aliquot of solution associated with each treatment (500 ml) was dispensed onto filter paper inside a glass Petri-dish. One, newly eclosed (± 5 days post-eclosion) adult O. insidiosus, selected from our laboratory colony, was transferred into each Petri dish. The Petri dishes were maintained in the laboratory at 25 ± 5 °C and constant light for 96 hours of exposure to estimate the direct effects of the pesticides and pesticide mixtures on O. insidiosus adult survival. The number of live and dead O. insidiosus adults was recorded after 24, 48, 72, and 96 hours. Also, after 96 hours, any surviving O. insidiosus adults were individually transferred into a Petri dish with 20 western flower thrips adults to assess any indirect effects of the pesticides on predation. We found that the fungicides (aluminum tris, azoxystrobin, fenhexamid, and kresoxim-methyl), insect growth regulators (azadirachtin, buprofezin, kinoprene, and pyriproxyfen), botanical (Capsicum oleoresin extract, garlic oil, soybean oil), and entomopathogenic fungi (Beauveria bassiana and Metarhizium anisopliae) were not directly harmful to adult O. insidiosus with 80% to 100% adult survival after 96 hours. However, the pesticides; abamectin, spinosad, pyridalyl, chlorfenapyr, tau-fluvalinate, imidacloprid, dinotefuran, acetamiprid, and thiamethoxam were highly detrimental to survival of adult O. insidiosus (0% to 60% adult survival) after 96 hours. The pesticide mixtures of abamectin + spinosad, and chlorfenapyr + dinotefuran negatively impacted O. insidiosus (0% to 20% adult survival) whereas the pesticide mixture of azadiracthin + B. bassiana did not negatively affect O. insidiosus (100% adult survival). All western flower thrips adults were killed by surviving O. insidiosus adults after 48 hours indicating no indirect effects of the pesticides on predation.