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ARS Home » Northeast Area » Ithaca, New York » Robert W. Holley Center for Agriculture & Health » Emerging Pests and Pathogens Research » Research » Publications at this Location » Publication #320965
Title: Comparative efficacy of emulsifiable-oil, wettable-powder, and unformulated-powder preparations of Beauveria bassiana against the melon aphid Aphis gossypii

Author
item Wraight, Stephen
item FILOTAS, MELANIE - Cornell University
item SANDERSON, JOHN - Cornell University

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2016
Publication Date: 5/9/2016
Citation: Wraight, S.P., Filotas, M.J., Sanderson, J.P. 2016. Comparative efficacy of emulsifiable-oil, wettable-powder, and unformulated-powder preparations of Beauveria bassiana against the melon aphid Aphis gossypii. Biocontrol Science and Technology. 26:894-914.

Interpretive Summary: Aphid pests have proven difficult targets for microbial biological control with fungal pathogens. These insects feed by piercing plants and sucking the sap and thus do not pick up fungal spores from contaminated foliage during the act of feeding, as do chewing insects. Many aphids also prefer to feed on new foliage in the crowns of plants where they may be exposed to environment conditions unfavorable for fungal infection. Development of effective formulation and application systems is thus critical to successful use of these agents for aphid control. Oils are known to act as effective spray stickers and have been claimed to improve efficacy of fungal pathogens under dry conditions. Oil formulation is thus considered one of the most promising technologies for improving efficacy of spray applications targeting aphids and other sucking insects. The objective of this study was to investigate effects of oil versus water formulation on the efficacy of spores of a common insect pathogenic fungus (Beauveria bassiana) applied against the melon aphid (Aphis gossypii) under variable humidity conditions. In laboratory tests, formulation in emulsifiable oil did not increase the capacity of the fungus to infect aphids under dry conditions nor increase its virulence compared to unformulated fungus. Nevertheless, the oil-based formulation was consistently more effective than a wettable powder formulation. The results support a hypothesis that oils function primarily as spray spreader/stickers, improving the efficiency of spray applications. These results increase our knowledge of the action of oils in biopesticide sprays and will guide future studies aimed at increasing efficacy of fungal pathogens through improved formulations.

Technical Abstract: Aphicidal efficacy of two commercial formulations of Beauveria bassiana strain GHA conidia, an emulsifiable-paraffinic oil dispersion (OD) and a clay-based wettable powder (WP), were compared to unformulated conidia in laboratory tests with adult melon aphids (Aphis gossypii). For the initial 24 hour post-treatment, aphids were incubated under high (100 percent) versus “low” (75 plus or minus 3 percent) relative humidity (RH) conditions, and over the subsequent 6 days, all aphids were incubated at the low RH. Mortality among aphids treated with the carrier blanks was low (6-11 percent) in the low-RH assays and was not affected by formulation. In the high-RH assays, the formulation blanks produced 17-20 percent mortality in all cases except for the highest rate of the OD blank (44 percent mortality). Mortality did not differ between the OD and unformulated conidia treatments, and factorial ANOVA revealed no synergism of B. bassiana activity by the OD carrier ingredients. In contrast, WP formulation had a small, but significant, negative impact on fungal efficacy. Post-treatment relative humidity conditions had a highly significant effect, with mean LC50 across formulations being nearly 6.5-fold higher (3457 versus 539 conidia per square millimeter) at low vs. high RH; however, relative efficacy of the formulations was not affected by RH (no significant formulation x RH interactions). The OD formulation was significantly more effective than the WP, increasing mortality by a maximum of 34-percentage-points. There were no significant effects of formulation on probit regression slopes, even when data were not corrected for carrier effects. These findings support a hypothesis that oils increase the efficiency of spray applications by functioning primarily as spray spreaders/stickers.