Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/8/2003
Publication Date: 6/3/2003
Citation: LELAND, J.E., BEHLE, R.W. DEVELOPMENT OF MYCOINSECTICIDES FOR CONTROLLING TARNISHED PLANT BUGS ON WILD HOST PLANTS. NATIONAL COTTON COUNCIL BELTWIDE COTTON CONFERENCE. 2003. http://www.cotton.org/beltwide/proceedings.cfm
Interpretive Summary: The tarnished plant bug (Lygus lineolaris) is an important economic pest of cotton in the southern United States. Alternatives to chemical insecticide control practices are needed to mitigate environmental impacts and resistance development. Because populations develop in high numbers in wild host plants before moving into cotton, area-wide management in these wild host areas is a particularly attractive alternative. Entomopathogenic fungi have potential to be used as a biorational approach to controlling of tarnished plant bug populations developing on wild hosts. New isolates of the entomopathogenic fungus, Beauveria bassiana have been obtained from populations of tarnished plant bugs indigenous to the Mississippi Delta. These isolates are more virulent to tarnished plant bugs than commercial isolates currently available. Further evaluation of these new isolates will test their impact on beneficial insects and their spore production potential in simulated industrial production conditions as compared to commercial isolates. One major obstacle to the efficacy of entomopathogenic fungi is their inability to survive exposure to solar radiation. Novel formulation strategies involving coating spores with lignin derivatives were investigated. Coating B. bassiana spores with lignin improved their survival following exposure to solar radiation. Although these formulations remained virulent to tarnished plant bugs, the formulated spores were less virulent than unformulated spores. Further development of formulation strategies will focus on improvements related to shelf-life and infectivity.
Technical Abstract: Entomopathogenic fungi 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 BioAgriculture) 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.