Effectiveness of spinosad and spinetoram against the citrus gall wasp, Bruchophagus fellis (Hymenoptera: Eurytomidae), and their impacts on beneficial arthropods in citrus

The citrus gall wasp, Bruchophagus fellis, is a significant pest in Australian citrus production. It particularly affects Valencia citrus growers, as the available chemical control options are considered unsuitable due to persistence of residues and associated long withholding periods, or too costly. We investigated the effectiveness of two spinosyn-based foliar products, spinosad and spinetoram, for controlling B. fellis and their impact on beneficial arthropods in citrus orchards. Both chemicals demonstrated efficacy, with over 98% mortality in B. fellis adults within 24 h of direct application in laboratory tests. Residual toxicity assessments showed prolonged efficacy, with spinetoram remaining toxic to B. fellis for up to 21 days and spinosad for up to 14 days post-spray. Spinetoram appears more toxic to B. fellis than spinosad. A field trial confirmed efficacy of both active ingredients in reducing B. fellis infestations, particularly with well-timed applications before peak adult B. fellis emergence. A double-spray application of spinetoram (1 week apart) showed the most effective control, with 66% reduction in gall weights and 84% reduction in the proportion of large galls compared to the untreated control. Four important beneficial arthropods [Aphytis lingnanensis (Hymenoptera: Aphelinidae), Cryptolaemus montrouzieri (Coleoptera: Coccinellidae), Mallada signatus (Neuroptera: Chrysopidae) and Neoseiulus californicus (Acari: Phytoseiidae)] of Australian citrus orchards were selected for the toxicity studies. Spinosad and spinetoram appeared relatively safe to C. montrouzieri and M. signatus but were highly toxic to A. lingnanensis and N. californicus. Based on these findings, spinetoram could be a good foliar application option for Valencia growers to target adult B. fellis.