Submitted to: Asia Pacific Congress of Entomology
Publication Type: Proceedings
Publication Acceptance Date: 10/18/2009
Publication Date: 10/22/2009
Citation: Jin, X., Chen, J., Streett, D.A., and Weaver, M.A. 2009. Optimization of compatible non-ionic surfactant for formulation development of hydrophobic conidia of entomopathogenic fungi, Beauveria bassiana (Hypocreales: Cordycipitaceae) and Metarhizium anisopliae (Hypocreales: Clavicipitaceae). Proceedings of the 6th Asia-Pacific Congress of Entomology. Beijing, P. R. China, October 18-22, 2009. pp. 145.
Technical Abstract: Aerial conidia, especially dried conidia of entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae are hydrophobic, and therefore surfactants are needed for developing water-based formulations in laboratory studies, greenhouse bioassays, and field trials as well as commercial product development. In most publications, selection of a surfactant for aerial conidia of either B. bassiana or M. anisopliae is solely based on compatibility between the surfactant and the conidia. Thus, the selected surfactant should reduce water surface tension and not have harmful effects on conidial viability. Non-ionic surfactants have been generally considered less toxic to microorganisms than ionic surfactants, which makes them the ideal candidates for use in water-based conidial suspensions. Non-ionic surfactants consist of a molecule that combines both hydrophilic and lipophilic groups (polar and non-polar groups) and the balance of the size and strength of these two groups is called hydrophilic-lipophilic balance (HLB number. Using the HLB number for optimizing surfactants has been applied to almost all industries wherever surfactant is needed in product development, including pharmaceutical, food, cosmetic, and pesticide and herbicide formulations. Recent research indicated HLB number system was also used in formulation development of microbial pesticides when hydrophobic aerial conidia were employed as active ingredient. Methods for measuring HLB numbers of B. bassiana and M. anisopliae are different; the rotary shaking method is suitable for B. bassiana, while the direct dropping method is more appropriate for M. anisopliae. Optimization of a compatible non-ionic surfactant will reduce the wetting time, increase conidial density in suspension, improve and synchronize conidial germination in field application. Our bioassay results also indicated that optimization based upon HLB number did not negatively affect parameters associated with efficacy, while proving desirable physical properties of a formulation.