Differential Feeding Responses of Several Bee Species to Sugar Sources Containing Iridomyrmecin, an Argentine Ant Trail Pheromone Component

Abstract

Pollinators such as bees need reliable access to nectar resources. However, competition for these carbohydrate rewards can be high among floral visitors. Moreover, invasive insects may further restrict pollinator access to flowers. For example, invasive Argentine ants (Linepithema humile) are known to harass and displace pollinators from flowers and reduce nectar reward acquisition. The foraging behavior of bees is strongly influenced by numerous chemical cues and signals at the flower. Thus, to avoid aggressive floral visitors, bees may use chemical cues when deciding whether or not they forage on the flower. Here, we demonstrate that Argentine ants deposit a pygidial gland chemical, iridomyrmecin, on a sugar source while feeding. Based on two-choice laboratory assays conducted with three commercially available bee species, the presence of iridomyrmecin in the sugar resource influenced the foraging decisions of Megachile rotundata and Osmia lignaria, but not those of Apis mellifera. Detailed insights into the chemical signals left by ants at floral resources and their effects on foraging decisions by pollinators can provide vital information for understanding the magnitude and mechanisms of impacts invasive ant species might have on pollinators.