Imidacloprid Effects on Acalymma vittata (Coleoptera: Chrysomelidae) and Bacterial Wilt in Cantaloupe

The systemic nitroguanidine insecticide imidacloprid was investigated in cantaloupes, Cucumis melo L. variety reticulatus, for management of Acalymma vittata (F.) and bacterial wilt caused by Erwinia tracheiphila (E. F. Smith) Holland that is vectored by this beetle. The influence of management strategies using imidacloprid upon plant growth and development, beetle population dynamics, and bacterial wilt disease incidence and severity was evaluated. Application of imidacloprid to seedlings at higher doses caused short-term marginal leaf necrosis, and biomass of seedlings was reduced in an approximately linear pattern with increasing dose on a log scale up to 0.01 g (AI) per plant. Application to seedlings at doses low enough to avoid any phytoxicity resulted in adult A. vittata mortality rates that declined exponentially with time. Exponential decay models of bioassay data suggested ≈11 d of 100% adult mortality was achieved with low rates applied to seedlings before transplanting. Applications to seedlings delayed adult immigration, and the combination of seedling application and limited foliar sprays resulted in significant increases in yield. Addition of imidacloprid at low rates to seedlings combined with 2 foliar sprays, or application to seedlings combined with an application through drip irrigation and 2 foliar sprays, was not effective in reducing the proportion of cantaloupe plants that showed bacterial wilt symptoms but did significantly reduce severity of the disease. The results suggest that low rates of imidacloprid applied before or near the time of transplanting, at times combined with few foliar sprays, could dramatically improve crop productivity via influence upon both a herbivore and a plant pathogen vectored by the herbivore.