Laboratory evaluation of insecticides for the control of Delia planipalpis (Diptera: Anthomyiidae), a nascent pest of broccoli (Brassicaceae) in Mexico

The radish fly, Delia planipalpis Linnaeus (Diptera: Anthomyiidae), is an emerging pest of broccoli and brassicaceous crops (Brassicaceae). The fly oviposits close to the stem of broccoli plants, and larvae feed within the stem and then pupate in the soil. Due to D. planipalpis’s recent appearance as a pest, no insecticides are registered for its management in Mexico. This study evaluated the efficacy of 13 synthetic and biological insecticides against different developmental stages through laboratory bioassays. Neonicotinoid-based products were highly toxic to the larvae, especially when applied via root irrigation, with thiamethoxam, clothianidin, and imidacloprid showing systemic activity. Thiamethoxam- and spinetoram-based products were also effective when applied to the stem oviposition site as a spray. A clothianidin-based product demonstrated moderate ovicidal activity, and bifenthrin had moderate residual activity against adult flies. A pyriproxyfen-based product effectively suppressed adult emergence. Products based on spirotetramat, neem (Meliaceae), and Tagetes (marigold) (Asteraceae) extracts and the microbial insecticide Bacillus thuringiensis var. israelensis (Bacillaceae) were ineffective against this pest. Spinosad and Sterneinema feltiae (Rhabditida: Steinernematidae) were not highly effective but could be used together with other control strategies in organic production. Neonicotinoids, spinetoram, and pyriproxyfen are promising options to validate in field trials for the management of D. planipalpis in broccoli.