Development of a Fatty Acid Emulsifiable Concentrate Formulation as a Biopesticide for Livestock Fly Control

Development of a Fatty Acid Emulsifiable Concentrate Formulation as a Biopesticide for Livestock Fly control ABSTRACT While medium chain fatty acids (octanoic nonanoic and decanoic acids called C8910) are generally regarded as safe (GRAS) they have contact insecticidal activities against certain insects and arthropods. This activity can be increased by increasing the dose but higher doses can result in greater potential for skin and eye irritation when exposed to mammals and increased phytotoxicity when exposed to plants. This study was undertaken to increase the pesticidal potency of the fatty acids by formulation in aqueous emulsion along with adjuvant. Compared to a mineral oil formulation of C8910 previously registered with the US EPA for livestock fly control the aqueous emulsion formulations had significantly lower skin absorption and higher residue on the skin surface where the fatty acids must remain to affect the flies. Following this Phase I finding we focused on emulsions of a 2 component mix of octanoic and decanoic acids (C8C10) as actives since laboratory studies had shown that C8C10 had equal or better pesticidal activity vs. stable flies as compared to the 3 component fatty acid mix (C8910). Further a C8C10 formulation was successfully registered with OMRI for organic production. The inclusion of a proprietary adjuvant with the C8C10 formulations increased pesticidal performance and residual activity. While the adjuvant had no known pesticidal activity by itself and lab tests with 1% adjuvant in distilled water showed little or no insecticidal effect lab tests with house flies stable flies horn flies and cockroaches demonstrated that insect incapacitation was more rapid and mortality (incapacitation at 24 hours post treatment) was significantly higher when the adjuvant was present in the fatty acid formulation. Performance against permethrin resistant stable and horn flies was also increased. A University of Arkansas field study evaluated C8C10 in automated sprayers with and without adjuvant versus horn flies on pastured cattle. The addition of adjuvant (formulation No. XPS-144) gave more rapid fly control compared to the fatty acids alone (XPS-143); XPS-144 had equivalent efficacy to permethrin/PBO during the spray period (94-98% control) but with greater residual efficacy (XPS-144 maintained horn fly count below the economic injury level 1 week after cessation of spraying while permethrin/PBO fly count rose to control levels above 300 flies/animal). A similar study in the central valley of California using manual sprayers demonstrated greater residual efficacy when the adjuvant was present maintaining horn fly numbers at about 100/animal well below the economic injury threshold . In conclusion these Phase I results demonstrated that good fly control can be provided with C8C10 formulations with adjuvant whether used in manual sprayers or in an automated device (Fig 1). Phase II studies will determine the minimum concentration and/or spray frequency of XPS-144 necessary for adequate fly control. A concentrate corresponding to XPS-144 will be developed. Laboratory studies will investigate the residual effect of the adjuvant.