Susceptibility to insecticides of Megalurothrips usitatus (Bagnall) and Frankliniella insularis (Franklin) (Thysanoptera: Thripidae) infesting Lablab purpureus in Florida

Megalurothrips usitatus is a serious pest of leguminous crops that originates from the Asian tropics. Since 2020, it has become established in Florida, Mexico, parts of Central America, and parts of the Caribbean. In south Florida, M. usitatus has significantly impacted the snap bean (Phaseolus vulgaris) industry. It has also established in specialty legumes including lablab bean (Lablab purpureus), which supports high populations of Frankliniella insularis. In response to the establishment of M. usitatus in south Florida, populations of M. usitatus were collected from lablab bean and subjected to a maximum dose insecticide laboratory bioassay to determine susceptibility to eight insecticides. The top labeled rate of abamectin, acetamiprid, cyantraniliprole, flupyradifurone, lambdacyhalothrin, methomyl, spinetoram, and tolfenpyrad was tested against seven populations of M. usitatus collected from farms managed by two different growers. Six populations of F. insularis collected from the same fields were subjected to the same bioassays. Overall, F. insularis, which is not documented as a pest in Florida, was more susceptible to insecticides than M. usitatus. Abamectin, cyantraniliprole, methomyl and spinetoram were effective against M. usitatus under the conditions of the bioassay, with survival ranging from 6.4% for spinetoram to 13.9% for abamectin. Percentage survival for either species treated with lambda-cyhalothrin did not differ significantly from the untreated control. Although one grower applied insecticides more intensively than the other, there was no statistical difference in survival among populations collected from the two different growers. Implications and priorities for managing newly established invasive thrips are discussed.