Relative Susceptibility of Pecan Weevil Fourth Instars and Adults to Selected Isolates of Beauveria bassiana

The relative susceptibility of fourth instar and adult pecan weevils, Curculio caryae (Horn), to seven isolates of the entomogenous fungus, Beauveria bassiana (Balsamo) Vuillemin, was assessed in laboratory bioassays. Lethal times as determined by probit analysis indicated that susceptibility to the isolates was in the decreasing order ARSEF-738 ≥ CCG1 ≥ ARSEF-150 ≥ 143-Mono ≥ AGBR1 ≥ ARSEF-252 ≥ AF-4 for adults and CCG1 ≥ ARSEF-738 ≥ AF-4 ≥ ARSEF-150 ≥ AGBR1 ≥ ARSEF-252 ≥ 143-Mono for fourth instars. In laboratory assays, exposure of fourth instars to conidia in soil showed that larvae were infected after burrowing through a layer of conidia mixed in the soil and that mortality levels were 73% at concentrations of 107 spores/g. Field tests of the "barrier" treatments yielded 23, 34, and 2% mortality for AF-4, CCG1, and ARSEF-252, respectively.