ABSTRACT

The efficacies of entomopathogenic fungal isolates are being evaluated for microbial biocontrol of tarnished plant bugs (Lygus lineolaris). Eight isolates of entomopathogenic fungi were compared for relative virulence to L. lineolaris adults. These isolates included the following: 1) two commercial Beauveria bassiana isolates used in the mycoinsecticides Mycotrol® (Emerald Bio-Agriculture) and Naturalis-L® (Troy Biosciences) (B. bassiana ARSEF 6444 and ARSEF 3097, respectively); 2) an isolate of Metarhizium anisopliae (ARSEF 3540) selected for its demonstrated virulence to L. lineolaris; and 3) five isolates of B. bassiana from L. lineolaris. One of the isolates from L. lineolaris (B. bassiana ARSEF 3769) was obtained in Arkansas and had previously been tested against L. lineolaris in field trials and the remaining four are new isolations from L. lineolaris in Mississippi. Those isolates that were obtained from L. lineolaris were more virulent to L. lineolaris adults than the two commercial B. bassiana isolates and the M. anisopliae isolate on the basis of LT₅₀ and LT₉₀ values. In addition, L. lineolaris cadavers killed by isolates that were obtained from L. lineolaris sporulated more rapidly than cadavers killed by B. bassiana (ARSEF 6444). We evaluated survival of conidia from B. bassiana (ARSEF 6444) and this five isolates from L. lineolaris following exposure to simulated solar radiation. Although there were differences among these isolates regarding their tolerance to solar radiation, each of the isolates was rapidly inactivated by solar radiation. Novel formulation strategies were tested that used water soluble lignin derivatives as sunscreens for protecting spores from solar radiation. Beauveria bassiana spores (ARSEF 6444) were coated with water soluble lignin derivatives using spray drying techniques. Lignins were either cross-linked with calcium ions to reduce the water solubility of the coating or not cross-linked to produce a highly water soluble spore coating. Spores coated with cross-linked or non-cross linked lignin were suspended in either a water (0.04% Silwet L77) or oil (70% Shellsol OMS : 30% cotton seed oil) carrier. Non coated spores suspended in water and oil carriers were used as controls. A greater percentage of spores survived exposure to solar radiation in those treatments where the spores remained coated when suspended in the carrier. The most infective formulation against L. lineolaris adults was non-coated spores suspended in water. Non-coated spores in oil, cross-linked lignin coated spores in water, non-cross linked lignin coated spores in water, and non-cross linked lignin coated spores in oil all demonstrated similar efficacy. The least infective formulation was cross-linked lignin coated spores in oil. These results indicate a potential for improving the efficacy of mycoinsecticides against L. lineolaris through isolate selection and formulations that improve their environmental persistence.