Effect of European Chafer Larvae (Coleoptera: Scarabaeidae) on Winter Wheat and Role of Neonicotinoid Seed Treatments in Their Management

ABSTRACT A critical density of four third-instar larvae per 900 cm2 for European chafer, Rhizotrogus ( Amphimallon) majalis(Razoumowsky), in winter wheat, Triticum aestivum L., was derived from smallplot greenhouse and field experimentsconducted under favorable crop growing conditions at several Ontario and Michigan locations from 2001–2003. On average, plant weight was decreased by 14% and plant stand by 11% between zero and four larvae per 900 cm2. In a commercial field under moisture stress, a yield loss of 35% occurred at a density of two third-instars per 900 cm2. In short-term greenhouse experiments, density-dependent mortality was evident, whereas low larval recovery in field experimentsindicates a high level of overwinteringmortality, regardless of larval density. Winter wheat seed treatmentsof neonicotinoidinsecticides, clothianidin, imidacloprid, and thiamethoxamprovided protection from damage by larvae, but the level of protection was inconsistent between greenhouse and field small plots,...