D3012: Improving management of the larger grain borer, Prostephanus truncatus, and the maize weevil, Sitophilus zeamais

The invasive larger grain borer, Prostephanus truncatus and Sitophilus zeamais are devastating stored product pests of maize and cassava. This project focuses on enhancing knowledge of P. truncatus and S. zeamais management through chemical control, improving understanding of interspecific competition in grain columns, and elucidating how these species potentially vector microbes. To enhance chemical control, we investigated the efficacy of a novel insecticide formulation (S-methoprene + deltamethrin + piperonyl butoxide; Gravista®) compared to an existing commercial standard formulation without synergist (Diacon IGR+®), and water-treated controls. We found multiple-fold mortality induction and movement reduction compared to the control, and in a dispersal apparatus we found P. truncatus dispersal was significantly reduced by 90–97% after exposure to either formulation compared to the control. Additionally, we evaluated the outcome of interspecific competition between P. truncatus and S. zeamais in monolayers of maize under different densities after 1 and 7 d in pure or mixed colonies. Both species aggregated together and were correlated to the same location as heterospecifics. Prostephanus truncatus damage was lessened and shifted upwards with S. zeamais present. Finally, the ability of both species to vector microbes after a 0–72 h dispersal period was assessed. Both species readily vectored several plant pathogenic microbes, including 21 taxa from 11 genera, notably Aspergillus, Penicillium, and Fusarium spp. Increasing dispersal period resulted in a third less microbial growth by S. zeamais after 72 h. This highlights the importance of behavioral ecology in IPM and suggests new tactics for these economically important species.