Biological control of the red flour beetle, Tribolium castaneum using entomopathogenic fungi

Abstract

In this project the factors influencing the efficacy of entomopathogenic fungi on Tribolium castaneum (Herbst.) were evaluated. Initially, the efficacy of commercial formulations of Beauveria bassiana (Naturalis-L), Metarhizium anisopliae (Met52) and Verticillium lecanii (Mycotal) was assessed with adults and different instar larvae of T. castaneum. Results showed that all fungi tested had a pathogenic impact on T. castaneum. Beauveria bassiana and M. anisopliae were more effective than V. lecanii at the concentrations tested. To investigate whether combining dsRNA with fungi would improve the performance against T. castaneum, low concentration fungal spore formulations of B. bassiana and M. anisopliae in combination with the dsRNA of the T. castaneum small conductance calcium-activated potassium channel protein (SK) and potassium voltage-gated channel protein Shaker (SH) genes were evaluated. The combined treatments (fungi and dsRNA) were more successful than fungi or dsRNA treatment alone. To assess the effects of quinones secreted by T. castaneum on infection by the fungi the effects of B. bassiana and M. anisopliae on T. castaneum adults were assessed with three different types of flour medium: fresh, naturally conditioned and conditioned by synthetic 2-methyl-1,4-benzoquinone with high or low levels of quinone. Scanning electron microscopy was used to examine the adherence and germination of fungal spores on the adults. Synthetic 2-methyl-1,4-benzoquinone medium was inhibitory to the growth of fungi. These differences may be due to both the number of spores found on the insect and their germination. The effects of fungal application on insect behaviour immediately after treatment were assessed. Adults which were treated with water tended to move larger distances, while adults treated with B. bassiana covered smaller distances at slower speeds. The demonstration that Tribolium castaneum is susceptible to the commercial formulations of M. anisopliae, B. bassiana and V. lecanii tested is novel. The fungal strains tested have possible use as a management tool against T. castaneum and other stored-product pests.