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Title: Cumulative impact of a clover cover crop on the persistance and efficancy of Beauveria bassiana in suppressing the pecan weevil (Coleoptera: Curculionidae)

item Shapiro Ilan, David
item GARDNER, WAYNE - University Of Georgia
item WELLS, LENNY - University Of Georgia
item Wood, Bruce

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2012
Publication Date: 4/1/2012
Citation: Shapiro Ilan, D.I., Gardner, W., Wells, L., Wood, B.W. 2012. Cumulative impact of a clover cover crop on the persistance and efficancy of Beauveria bassiana in suppressing the pecan weevil (Coleoptera: Curculionidae). Environmental Entomology. 41:298-307.

Interpretive Summary: The pecan weevil is a key pests of pecans in the southeastern US as well as Texas and Oklahoma. Development of novel environmentally friendly methods to control pecan weevil is needed. A naturally occurring beneficial fungus (called Beauveria bassiana) can kill the pecan weevil. A new method to increase the efficacy of this fungus was discovered. Planting clover in the pecan orchard was found to increase the persistence of the native fungus and enhance its ability to kill the pecan weevil. Therefore, the use of clover as a cover crop in pecan orchards is likely to have added benefits in terms of natural pest control, and the amount of chemical pesticides that are needed may be reduced.

Technical Abstract: Curculio caryae (Horn), is a key pest of pecans. Endemic levels of the entomopathogenic fungus Beauveria bassiana can occur in pecan orchards and contribute to natural control of C. caryae. Commercial formulations of the fungus can also be applied for suppression of C. caryae. We hypothesized that a clover cover crop would enhance B. bassiana efficacy and persistence (e.g., by protecting the fungus from harmful environmental conditions). To test the hypothesis, we conducted field trials in a pecan orchard in Byron, GA in 2009 and 2010. The study included four treatments arranged in a factorial with two levels of fungus (endemic fungus only, and application of a commercial B. bassiana product), and two levels of clover (white clover, Trifolium repens L. and no clover). In 2009, greater prevalence of B. bassiana conidia was detected in plots receiving fungal applications compared with no fungus applications, and no clear effect of clover was observed in plots that received B. bassiana applications in both years. In 2010, B. bassiana prevalence in the endemic fungus plus clover treatment was higher than endemic fungus without clover, and was similar to plots that received additional B. bassiana applications. Mortality of C. caryae (averaged over the sampling periods) ranged between 68-74% in plots receiving B. bassiana applications and 51-56% in plots with endemic fungus only. C. caryae mortality and mycosis data also provided evidence that endemic B. bassiana efficacy was enhanced by clover relative to plots without clover (with no clear clover effect on plots receiving fungus applications). Thus, we conclude that natural control of C. caryae can be increased by planting clover in pecan orchards that contain endemic populations of B. bassiana.