Biology and Management of Argentine Ants in California Vineyards

Argentine ants exacerbate mealybug populations in coastal California vineyards by protecting them from natural enemies and in return collecting a carbohydrate-rich food source. Conventional ant controls were only moderately effective at controlling ants and included toxic,broad-spectrum pesticide sprays, which disrupt natural enemies, and dry, protein-based baits,which are unattractive to sugar-feeding ants. Over the last 5 years, we have worked to develop a sustainable ant control program, dispensing reduced-risk insecticides as liquid, sugar-based baits.These baits do not disrupt non-target species, nor do they contaminate groundwater (a concern with barrier insecticide sprays). Originally our system, although effective for grape and obscure mealybug control, was labor and material intensive, both of which were prohibitive to its adoption on a large scale by growers. We have fine-tuned various aspects of the bait program, and now report that our work in this area is near completion. As of 2006, several bait stations, including one designed as part of this project, can be legally deployed in vineyards and orchards (US EPA-ChemSAC), two baits on which we have collected efficacy data have cleared the US EPA registration process and should be available in 2007-08, and we have 2 years of data addressing optimal density and timing of bait deployment. In 2006, we continued testing commercially available ant products, in order to provide growers with information on their efficacy, and initiated tests on new bait matrices containing amino acid additives and designed to be more attractive to ants than a simple sucrose solution. We also concluded multi-year studies on bait density and temporal deployment, designed to optimize bait delivery to the ants. Bait delivery should coincide with optimal foraging times and nest-induced demand for resources, as delineated by our previous bait trials and studies of Argentine ant nest biology and dispersal pattern. Since our studies on the bait program are nearing completion, this year we began to focus on aspects of the ant-homopteran-natural enemy complex which remain unanswered. These include the mechanism by which ants interfere with parasitism and the effect of ants on predatory insects. Additionally, with an ant baiting program in place in a Central Coast vineyard, we were able to resume distribution studies of the encyrtid parasitoids that were released in 1999-2000. We surveyed vineyards to quantify establishment rates and used potted plants and mealybugs collected during surveys to recover adult parasitoids. With these studies, we have collected the background information necessary to provide growers a complete understanding of the ant bait program, including aspects of bait placement, initiation and duration of baiting, and density of bait stations per acre. This information continues to be extended to growers in the form of invited talks, informal interactions, a UC-ANR fact sheet, and articles in trade and peer-reviewed journals. We have also collected initial data on the interactions between Argentine ants and natural enemies, which will give us a better understanding of their interactions and provide impetus for future studies on the biology and behavior of these insects.