Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2008
Publication Date: 3/15/2008
Citation: Jin, X., Streett, D. A., Dunlap, C. A., Lyn, M. E. 2008. Application of hydrophilic-lypophilic balance (HLB) number to optimize a compatible non-ionic surfactant for dried aerial conidia of Beauveria bassiana. Biological Control. 46: 226-233. Interpretive Summary: Beauveria bassiana is one of the most promising entomopathogenic fungi used in biological control of a variety of pests. Spores of B. bassiana do not readily mix with water so surfactants are needed to suspend the spores in commercial formulations. A classification system was used to determine the optimal surfactant for formulations of two B. bassiana strains, NI8 and GHA. This classification system allows us to predict surfactant behavior and to reduce the labor required to select an optimal surfactant for a commercial formulation.
Technical Abstract: The hydrophilic-lipophilic balance (HLB) number system was used to optimize a compatible non-ionic surfactant, TDA(polyoxyethylene tridecyl ether) in formulations for two Beauveria bassiana strains, NI8 and GHA. The optimal HLB number for TDA was determined on the basis of wetting times for conidial powders. The results indicated that optimal HLB number of TDA for B.bassiana strain NI8 was 8, while the optimum HLB number for strain GHA was 10. The optimized TDA surfactants required significantly less wetting times than the commonly used laboratory surfactants, Triton X-100, Span 80 and Tween 80. These optimized TDA surfactants were further characterized on their ability to produce conidial suspensions of the two strains in 5 minutes of mixing, TDA HLB 8 and TDA HLB 10 produced suspensions of 1.8 X 108 and 1.6 X 108 conidia/ml of NI8 and GHA, respectively. These conidial levels were significantly higher than those in Triton X-100, Span 80, and Tween 80 suspensions after the same mixing time. In addition, germination assays showed that TDA HLB 8 promoted significantly higher germination rates of strain NI8 than those observed in other commonly used laboratory surfactants. However, the germination rates of the GHA strain were unaffected by any of the surfactants tested. The efficacy of the conidial suspensions was confirmed with assays against Lygus lineolaris. Bioassay results indicated that there were no significant differences in sporulated mortalities because of surfactants. These results suggest optimization based upon HLB number will not negatively impact parameters associated with efficacy, while providing desirable physical properties.