The dispersal capacity of the invasive larger grain borer (Prostephanus truncatus) and the cosmopolitan maize weevil (Sitophilus zeamais) after exposure to a novel and reduced-risk insecticide

The larger grain borer (Prostephanus truncatus, LAGB) and the maize weevil (Sitophilus zeamais, MW) are major pests of stored maize. With the phase-out of methyl bromide, our most effective fumigant after harvest, and increasing resistance to phosphine, the most commonly used fumigant, there is a need for alternative management tactics. Here, we test the effectiveness of a novel reduced-risk insecticide (insect growth regulator + pyrethroid + synergist; tradename Gravista) compared to an older formulation (insect growth regulator + pyrethroid; tradename IGR+) at reducing the horizontal dispersal capacity to food patches by both of these stored product species. To do this, we used a dispersal apparatus (PVC pipe with baited pitfall trap) where we introduced cohorts of adults after exposure on concrete arenas and gave them 48 h to disperse to a novel food source consisting of 15 g of maize. The dispersal capacity for LAGB, measured as the number making it to the novel food source, was significantly impaired after exposure to both the insecticide formulations compared to the control treatment. Overall, these results suggest that this new insecticide combination is a very promising tool for controlling an invasive insect in warehouses where maize grains are stored, and could be incorporated in integrated pest management programs to protect stored maize and improve food security.