Trunk Perimeter Applications of Beauveria bassiana to Suppress Adult Curculio caryae (Coleoptera: Curculionidae)¹

The pecan weevil, Curculio caryae (Horn), is a key pest of pecans. Entomopathogenic fungi, such as Beauveria bassiana (Balsamo) Vuillemin, can infect this pest. Our objectives were to determine the potential of B. bassiana, to suppress emerging C. caryae adults when applied to soil around pecan tree-trunks, and to determine persistence of B. bassiana in the soil. In 2000 and 2001, B. bassiana was applied to soil in a 2 m band around pecan tree trunks. Naturally emerging C. caryae adults, caught after they crawled to the trunk, were brought to the laboratory to determine percentage mycosis. In Byron, GA, irrigation was applied to one-half of the plots, whereas, in Griffin, GA irrigation was not applied. In Byron, in both years, we observed greater fungus-induced mortality in plots that received B. bassiana without irrigation than in plots that received B. bassiana with irrigation or in the checks (with and without irrigation). In Griffin, in the year 2000, we observed higher C. caryae mortality in B. bassiana treated plots than in non-treated plots, whereas 2001 results showed no difference. Although we observed up to 95% B. bassiana-induced mortality within the first 3 d post-application, treatment effects did not persist beyond the first week post-application. Future research should focus on extending the persistence of B. bassiana suppression. Estimates of conidia production per B. bassiana infected insect yielded up to 4.2 × 10⁹ suggesting some recycling might occur in the soil.