Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2009
Publication Date: 10/2/2009
Citation: Behle, R.W., Compton, D.L., Laszlo, J.A., Shapiro Ilan, D.I. 2009. Evaluation of soyscreen in an oil-based formulation for UV protection of Beauveria bassiana Conidia. Journal of Economic Entomology. 102(5):1759-1766.
Interpretive Summary: Insect killing fungi used as biological insecticides, when applied in the field and exposed to sunlight, have short residual activity that limits their effectiveness as a pesticide. Formulating the biological insecticide with sunscreens may be effective, but may also require adding harsh chemicals to the formulation. We found evidence in laboratory experiments that the sunscreen known as SoyScreen (made from soybean oil) protected fungal conidia from harmful effects of simulated sunlight. Unfortunately, these benefits were not detected with field applications because the protective oils are absorbed by the treated plants. These results point to the need to continue formulation research in order to improve their efficacy while maintaining the “green” persona of biological pesticides. Developing this use for SoyScreen provided an added market for soy products, and benefits the biopesticides industry by improving the efficacy of environmentally friendly pest control products.
Technical Abstract: SoyScreen oil was studied as a formulation ingredient to protect Beauveria bassiana (Balsamo) Vuillemin conidia from UV degradation. Feruloylated soy glycerides, referred to as SoyScreen oil, are biobased ultraviolet-absorbing molecules made by combining molecules of soybean oil with ferulic acid. Conidia stored in SoyScreen oil for 28 weeks at 25, 30, and 35 deg. C retained viability as well as conidia stored in sunflower oil, demonstrating that SoyScreen did not adversely affect viability with prolonged storage. For samples applied to glass and exposed to simulated sunlight (xenon light), conidia in sunflower oil with or without sunscreens (SoyScreen or oxyl methoxycinnimate) had similar conidia viability after exposure. These oil formulations retained conidia viability better than conidia applied as an aqueous treatment. However, the 10% SoyScreen oil formulation applied to field grown cabbage and bean plants did not improve residual insecticidal activity when compared with aqueous applications of unformulated conidia or two commercial formulations when assayed against Trichoplusia ni (Hübner) larvae. Our results suggest that the oil applications lose UV protection because the oil was absorbed by the leaf. This conclusion was supported in subsequent laboratory exposures of conidia in oil-based formulations with UV screens applied to balsa wood, which absorbed the oils, lost protection and conidia viability decreased with light exposure. As a result, additional formulation techniques, such as encapsulation to prevent separation of the protective oil from the conidia and other ingredients, may be required to extend protection when oil formulations are applied in the field.