Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2006
Publication Date: 8/1/2006
Citation: Behle, R.W. 2006. Importance of direct spray and spray residue contact for infection of Trichoplusia ni larvae by field applications of Beauveria bassiana. Journal of Economic Entomology. 99(4):1120-1128. Interpretive Summary: Understanding specific interactions concerning the infection process for biopesticides will help to direct development of more effective formulations. The fungus, Beauveria bassiana, must contact the target insect to initiate infection, and this contact may result directly from the spray application or by contacting spray residue while target insects forage on the crop plant. Applications of commercial and experimental formulations of this fungus to bean and cabbage plants demonstrated that direct spray contact is important for control of caterpillars on both crops, and that contact with spray residue adds to the initial insecticidal activity for applications to cabbage. Differences in insecticidal activity of these biopesticide applications between the two crops demonstrates the need to address specific formulation considerations that are unique to each cropping system in order to maximize pest control with biological agents. This research will benefit the biopesticide industry by providing information to help direct formulation research to improve biopesticide products and ultimately provide new ecologically compatible insecticides for consumer use.
Technical Abstract: Commercial and experimental formulations of Beauveria bassiana strain GHA conidia were applied to field grown plants and artificially infested with Trichoplusia ni (Hübner) larvae to compare the relative insecticidal activities of primary spray contact and secondary contact with spray residue. All field applications of Beauveria formulations showed rapid loss of activity, expressed as a loss of conidia viability and loss of insecticidal activity during the first eight hours after application. In general, applications to cabbage, Brassica oleracea, resulted in nearly equal mortalities when comparing insects exposed by primary contact with those exposed by secondary contact, suggesting the potential for improving formulations to extend residual activity. For applications to beans, Phaseolus vulgaris, primary contact provided greater insect mortality than secondary contact. In contrast to the differences observed for larvae exposed in the field, larvae exposed in laboratory bioassays to field-collected leaf disks resulted in nearly identical mortalities for cabbage and bean plants. Two experimental formulations, intended to extend residual activity by shielding sunlight-reduced inactivation of conidia, did not provide the expected benefits when applied in the field.