Exploitation of synergistic effects between semiochemicals and Metarhizium brunneum against soil pests

Abstract

Root-feeding insects, such as the larvae of the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) and wireworms Agriotes spp. Eschscholtz (Coleoptera: Elateridae), the larvae of click beetles, are widely recognized as major soil pests, which influence agricultural productivity. Environmental concerns and a high risk of insecticide use as well as the lack of other efficient control options require new and effective strategies to target these pests. Two behavioral based control approaches, combining the use of the entomopathogenic fungus Metarhizium brunneum (Metschnikoff) Sorokin from the order Hypocreales (Ascomycota) and semiochemicals as efficacy enhancing agents, were tested to improve biological soil pest control. WCR larval control was evaluated with a “stress-and-kill” (SK) strategy in laboratory and greenhouse experiments using botanical repellents to increase the chance of contact and susceptibility with M. brunneum conidia. Wireworm control was tested with an “attract-and-kill” (AK) strategy in field and laboratory experiments, whereas the pest is lured towards M. brunneum conidia with an artificial carbon dioxide (CO2) source as an attractant. Both strategies were conducted with different formulation techniques to improve shelf-life and practical feasibility for an application in the field.