Laboratory Mortality and Mycosis of Adult Curculio caryae (Coleoptera: Curculionidae) Following Application of Metarhizium anisopliae in the Laboratory or Field

Abstract

The pecan weevil, Curculio caryae (Horn), is a key pest of pecans. The entomopathogenic fungi Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin are pathogenic to C. caryae. One approach to suppressing this pest may be to apply entomopathogenic fungi to adult C. caryae when they are emerging from the soil. However, thus far, laboratory screening of fungal isolates has been focused mostly on virulence to larval C. caryae, and published field trials on adult control have focused on application of B. bassiana. Our objective was to determine the potential of M. anisopliae to control emerging C. caryae adults. First, a laboratory test was conducted to compare 4 B. bassiana strains (Bb GA2, BbLA3, BbMS1, and GHA) and 3 M. anisopliae strains (F52, MaLA4, and MaLA7) for virulence to C. caryae adults. Virulence of the M. anisopliae strains was equal or greater than B. bassiana strains. Subsequently, a commercially available M. anisopliae strain (F52) was tested under field conditions when applied as a narrow fiber band that was impregnated with fungus and wrapped around the tree trunk, and/or when applied directly to the soil. In 2005, we applied M. anisopliae as trunk bands with or without additional application to the soil in the same plots. In 2006, we applied trunk bands or soil applications in separate plots. For 15 d posttreatment, weevils were trapped and transported to the laboratory to record mortality and mycosis. In 2005, weevil emergence was extremely low and statistical analysis was only feasible 3d posttreatment (at which time no treatment differences were detected), and 15 d posttreatment, at which time higher mortality and mycosis was observed in both the trunk band application and the trunk band + ground treatment compared with a nontreated control (and no difference between the two fungal treatments was detected). In 2006 overall average C. caryae mycosis was higher in trunk band and ground treatment compared with an untreated control, whereas average total mortality (from the fungus or other causes) was not different among treatments except at 8 d post treatment (in which only the band treatment was significantly greater than the control). It must be noted that our evaluation of efficacy was only an estimation of potential insect control (as opposed to actual field suppression of C. caryae) because our analysis was based on C. caryae mortality following transport to controlled environmental conditions. Nonetheless, our research indicates that trunk band or ground applications of M. anisopliae may have potential to cause significant infection in C. caryae populations.