Assessing the effectiveness of selected reduced-risk insecticides and malathion on blueberry gall midge (Diptera: Cecidomyiidae) and key parasitoids

Abstract

The blueberry gall midge, Dasineura oxycoccana, is a major blueberry pest in Florida and North America, primarily controlled with insecticides. However, their efficacy on D. oxycoccana and impact on natural enemies are poorly documented. We compared the effects of seven reduced-risk insecticides with malathion on larval and adult D. oxycoccana in laboratory bioassays. Acetamiprid showed the highest larval mortality, similar to malathion. Imidacloprid was effective after 2 h, while spirotetramat was effective after 3 h. On adults, cyantraniliprole and acetamiprid were as effective as malathion. Flupyradifurone began showing comparable lethality at 3 h, while spirotetramat, imidacloprid, and tolfenpyrad began inducing comparable mortality 6 h post-application. The same insecticides were evaluated for their effects on D. oxycoccana and their key parasitoids in two southern highbush blueberry plantings in North-central and Central Florida. A wetter-spreader adjuvant was added to spirotetramat as a ninth treatment. Spirotetramat + adjuvant effectively reduced adults and larval densities by up to 100% in the first year and adults by 59% and larvae by 56% in the second year. Acetamiprid reduced adult densities by 65% in 2019. Spinetoram reduced adults by 77% and larvae by 100% in 2019, while flupyradifurone reduced adults by 77% and larvae by 37% in 2020. These insecticides had minimal adverse effects on Platygaster spp. and overall parasitoid densities for both years. Based on these findings, there is potential for incorporating spirotetramat + adjuvant, flupyradifurone, spinetoram, or acetamiprid into a strategic rotational program with minimal impacts on natural enemies of D. oxycoccana.