Pyrethroids demonstrate effective insecticidal activity against ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) within tree fruit, nut, and ornamental production systems

The ambrosia beetles Xylosandrus crassiusculus (Motschulsky) and Xylosandrus germanus (Blandford) (Coleoptera: Curculionidae) are major pests in fruit, nut, and ornamental tree nurseries. Adult females tunnel into stressed trees, creating galleries in the sapwood and heartwood to cultivate their nutritional fungal mutualists, which are associated with branch dieback and tree death. The current management approach relies on trunk applications of permethrin and bifenthrin to decrease infestation risk in the United States. However, the efficacy of other insecticides has not been thoroughly evaluated. Fourteen trials were conducted in Virginia, South and North Carolina, Tennessee, and Georgia to evaluate the efficacy of various synthetic and biological or microbial insecticides as potential management tools in tree fruits, pecans, and ornamentals. Of the 24 active ingredients tested, only 5 pyrethroids (permethrin, bifenthrin, lambda-cyhalothrin, deltamethrin, and cypermethrin) reduced the numbers of entry holes in ethanol-infused bolts. The effectiveness of permethrin and bifenthrin against ambrosia beetles was consistent and superior to that of lambda-cyhalothrin, deltamethrin, and cypermethrin. Dinotefuran significantly reduced ambrosia beetle attacks in one trial. Spinosad, sulfoxaflor + spinetoram, chlorantraniliprole, cyantraniliprole, cyclaniliprole, tetraniliprole, tolfenpyrad, indoxacarb, isocycloseram, carbaryl, Burkholderia spp., Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae), Chromobacterium subtsugae PRAA4-1T (Neisseriales: Neisseriaceae), and Paecilomyces fumosoroseus (Wize) Kepler, B. Shrestha & Spatafora (Hypocreales: Cordycipitaceae) did not reduce beetle attacks. Thus, among insecticidal and biological products, only pyrethroid insecticides protect vulnerable trees by reducing entry holes from Xylosandrus spp. and remain a reliable tool for preventing their infestation in tree fruits, pecans, and ornamentals.