Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/5/2004
Publication Date: 6/4/2004
Citation: Leland, J.E., Behle, R.W. 2004. Formulation of the entomopathogenic fungus, beauveria bassiana, with resistance to uv degradation for control of tarnished plant bug, lygus lineolaris. National Cotton Council Beltwide Cotton Conference. Interpretive Summary: Certain fungi may be used to control insect pests. These fungi are being studied as an alternative for controlling a very important cotton insect pest, tarnished plant bug. One limitation to their ability to control insects in the field is that the fungal spores are killed by sunlight. This study investigated the potential for coating spores with a material from plants that would protect the spores from sunlight. By coating the spores with this material the survival of the spores in sunlight was improved by ten times. Coating the spores slightly reduced the ability of the spores to kill tarnished plant bug in the laboratory. However, if sunlight greatly reduces the fungal spores' potential for controlling this cotton insect pest in the field, then the protective advantages of the formulation may greatly improve the ability for using this fungus to control this insect.
Technical Abstract: Formulations are being developed for protecting entomopathogenic fungi from solar radiation to improve mycoinsecticide efficacy. Beauveria bassiana (GHA) spores were coated by spray drying with either water-soluble lignin or water-insoluble Ca2+-cross-linked lignin. These coated spores were suspended in either water (0.04% Silwet L77) or oil (Orchex 692) and compared with non-coated spores in water or oil to demonstrate the impact of the coating on spore survival under simulated solar radiation and pathogenicity to tarnished plant bug, Lygus lineolaris (Palisot de Beauvois). The rate of spore mortality under simulated solar radiation was approximately ten times lower for the three formulations in which spores in suspension remained coated with lignin (cross-linked lignin in water, lignin in oil, and cross-linked lignin in oil). The pathogenicity of the six formulation strategies did not differ significantly on the basis of LC50 values for direct spray applications to L lineolaris adults. However, the three lignin coated formulations that provided the greatest UV protection were slower to kill L. lineolaris (higher LT50 values). Adult L. lineolaris mortality was approximately 20 times lower when exposed to broccoli florets treated with B. bassiana formulations than when L. lineolaris was sprayed directly. In bioassays with treated broccoli florets, non-coated spores in 0.04% Silwet L77 were the most pathogenic. Under field conditions where solar radiation significantly impacts mycoinsecticide efficacy, the improved persistence of lignin coating formulations may outweigh the negative effects of reduced pathogenicity.