Relative attractiveness of toxic baits to Linepithema humile (Hymenoptera: Formicidae)

The invasive Argentine ant, Linepithema humile (Mayr) is a threat to urban, agricultural and natural environments and is associated with sap-feeding insects. Management is by toxic baits presented as liquids using sugar attractants and solids using protein. Baits are collected by workers and distributed within the colony through trophallaxis. In 2009 we observed poor performance by some products in two populations in Central Texas where >50% control was never achieved after several applications. We hypothesized that differences in dietary preference through the seasons affects outcome where workers do not collect enough for control. During 2010 we investigated how bait formulations can be enhanced by other foods. Baits included Extinguish Plus (EP), Esteem (E), Advance Carpenter Ant Bait (ACAB), Advance Carpenter Ant Bait 375A (ACAB375), MaxForce (MF), Amdro Ant Block (AAB) and Terro Liquid Baits (TLB). Foods to increase attractiveness included pulverized sugar and fish powder. Treatments were EP, EP+sugar, EP+fish, EP+sugar+fish, EP+fish (x2), E, E+fish, ACAB, ACAB375, MF, AAB and TLB. 1 ml of each formulation was deployed on lids on the ground. Ten replicates were used per treatment and followed for two hours (15 minute intervals) where workers were recorded. Bait formulations of TLB, ACAB and ACAB375 were most attractive. Granular baits mixed with food products did not improve attractiveness. We recommend a combination of solid and liquid baits (ACAB/ACAB375). We also recommend monitoring food preference thorough the year to determine triggers for treatments based on patterns since outcome may vary by region and season.