Experimentally guided development of a food bait for European fire ants.
Deployment of lethal food baits could become a control tactic for the invasive European fire ant (EFA), Myrmica rubra L. (Hymenoptera: Formicidae), because foraging ants carry the lethal food to their nest and share it with their nest mates, ultimately causing the demise of nests. Our objective was to develop a food bait that elicits a strong foraging response from EFAs, has extended shelf life, and is cost-effective to produce. To develop a bait composition with 'ant appeal', we ran two separate field experiments testing pre-selected carbohydrate sources (oranges, apples, bananas) and protein/lipid sources [tuna, pollen, sunflower seeds, mealworms (Tenebrio molitor L., Coleoptera: Tenebrionidae)]. Whereas foraging EFAs responded equally well to the three types of carbohydrates, they preferred mealworms to all other protein/lipid sources. In a follow-up laboratory experiment, the combination of apples and mealworms elicited a stronger foraging response from EFAs than either apples or mealworms alone. To help reduce bait ingredient costs, we tested house crickets, Acheta domesticus (L.) (Orthoptera: Gryllidae), as a less expensive mealworm alternative and found crickets and mealworms comparably appealing. Addressing the shelf life of baits, we tested freeze-dried and heat-dried apple/cricket combinations. Rehydrated freeze-dried baits proved as appealing as fresh baits and superior to rehydrated heat-dried baits, suggesting that freeze-drying may retain essential nutrients and/or aroma constituents. Insecticide-laced baits had no off-putting effect on foraging responses of worker ants and caused significant mortality. As freeze-drying is expensive, further research should investigate the preservation of moist food baits or the development of dry baits that are hydrated prior to deployment.