Effect of biopesticides on different Tetranychus urticae Koch (Acari: Tetranychidae) life stages

Tetranychus urticae Koch management in many specialty crops relies on intensive pesticide use and has led to rapid evolution of acaricide-resistant populations. These concerns, along with public concern regarding conventional pesticide safety, has generated interest in the use of biopesticides for managing T. urticae. Biopesticides evaluated included the bacterial products Grandevo DF 2 (Chromobacterium subtsugae strain PRAA4-1) and Venerate EP (Burkholderia spp. strain A396), the botanical-based product GOS Neem 7-way (azadirachtin), and the emulsified mineral oil product TriTek. Bifenazate (Acramite 50WP), a synthetic acaricide, and a water-treated control were included for comparative purposes. Contact and residual effects were evaluated using equivalent labeled field rates against T. urticae egg, larval, nymphal and adult life stages. Exposure route (contact or residual) was significant for eggs and larval and nymphal mortality after 24-h exposure. GOS Neem 7-way, TriTek, and Acramite were ovicidal under contact exposure only. Most biopesticides caused >50% larval mortality, yet only Acramite achieved 100% morality. Biopesticides were less toxic to nymphs relative to larvae, and Acramite and Grandevo DF 2 caused >50% nymphal morality. Only Acramite caused significantly higher adult mortality than the control 24-h post treatment. Except for Venerate, all treatments significantly reduced fecundity of surviving adults, with the greatest reduction by Acramite and Grandevo. With the exception of Acramite and a high rate of Grandevo, all treatments exhibited exponential population growth over five generations. However, most biopesticides evaluated exhibited significant mortality on various T. urticae life stages, and if incorporated into management schemes may be useful tools in acaricide resistance management programs for T. urticae.