Can spinosad-resistant Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) be managed with spinosad and predatory mites (Acari)?

Frankliniella occidentalis (Pergande) is a serious pest of a wide range of horticultural and ornamental crops. Populations resistant to most conventional insecticides, including–spinosad, have been detected. To control spinosad-resistant thrips, growers could use a ‘high-rate’/biological control strategy. The proposed strategy is based on a single application of spinosad at double the recommended application rate followed by releasing predatory mites (Acari), which are used as biological control agents of F. occidentalis. This study compared two resistance management strategies on a spinosad-resistant F. occidentalis strain: applying spinosad at twice the recommended rate, and spraying at twice the rate then releasing predatory mites, Typhlodromips montdorensis (Schicha), Neoseiulus cucumeris (Oudemans) and Hypoaspis miles (Berlese). Direct exposure to twice the recommended rate of spinosad killed 100% of all adults of all species of predatory mites. Spinosad residues aged 2–48 h were also highly toxic to adults of all three mite species, causing 96–100% mortality. Spinosad residues aged 48–168 h were less toxic to N. cucumeris than to T. montdorensis and H. miles. LT₂₅ of double the recommended rate of spinosad for T. montdorensis, N. cucumeris and H. miles were calculated as 6.02, 5.3, and 7.08 days, respectively. When released after applying spinosad, T. montdorensis was the most successful species in reducing thrips numbers, followed by N. cucumeris and H. miles. By releasing mites 6–7 days after a spinosad application, our results suggest that F. occidentalis can be effectively controlled. The practical implications of implementing a ’high-dose/biological control’ strategy are discussed.