Compatibility of Entomopathogenic Nematodes with Chemical Insecticides for the Control of <i>Drosophila suzukii</i> (Diptera: Drosophilidae)

The spotted-wing drosophila, <i>Drosophila suzukii</i> (Matsumura) (Diptera: Drosophilidae), is a pest that reduces the productivity of small fruits. Entomopathogenic nematodes (EPNs) and chemical insecticides can suppress this pest, but the compatibility of the two approaches together requires further examination. This laboratory study evaluated the compatibility of <i>Steinernema brazilense</i> IBCBn 06, <i>S. carpocapsae</i> IBCBn 02, <i>Heterorhabditis amazonensis</i> IBCBn 24, and <i>H. bacteriophora</i> HB with ten chemical insecticides registered for managing <i>D. suzukii</i> pupae. In the first study, most insecticides at the recommended rate did not reduce the viability (% of living infective juveniles (IJs)) of <i>S. braziliense</i> and both <i>Heterorhabditis</i> species. The viability of <i>S. carpocapsae</i> was lowered by exposure to spinetoram, malathion, abamectin, azadirachtin, deltamethrin, lambda-cyhalothrin, malathion, and spinetoram after 48 h. During infectivity bioassays, phosmet was compatible with all the EPNs, causing minimal changes in infectivity (% pupal mortality) and efficiency relative to EPN-only controls, whereas lambda-cyhalothrin generally reduced infectivity of EPNs on <i>D. suzukii</i> pupae the most, with a 53, 75, 57, and 13% reduction in infectivity efficiency among <i>H. bacteriophora, H. amazonensis, S. carpocapsae</i>, and <i>S. brazilense</i>, respectively. The second study compared pupal mortality caused by the two most compatible nematode species and five insecticides in various combinations. Both <i>Heterorhabditis</i> species caused 78–79% mortality among <i>D. suzukii</i> pupae when used alone, and were tested in combination with spinetoram, malathion, azadirachtin, phosmet, or novaluron at a one-quarter rate. Notably, <i>H. bacteriophora</i> caused 79% mortality on <i>D. suzukii</i> pupae when used alone, and 89% mortality when combined with spinetoram, showing an additive effect. Novaluron drastically reduced the number of progeny IJs when combined with <i>H. amazonensis</i> by 270 IJs and <i>H. bacteriophora</i> by 218. Any adult flies that emerged from EPN–insecticide-treated pupae had a shorter lifespan than from untreated pupae. The combined use of <i>Heterorhabditis</i> and compatible chemical insecticides was promising, except for novaluron.