UC Riverside

Bees are important in both agricultural and natural ecosystems for the pollination services that they provide. However, invasive ants that exploit floral nectar in these landscapes can act as resource competitors with bees. Competitive interactions between bees and ants can have repercussions for pollinator resource acquisition, plant or bee fitness, and, ultimately, ecosystem function. There are gaps in our knowledge about the behaviors and sensory mechanisms involved in interference competition between bees and nectivorous, non-pollinator antagonists. Here, we studied how invasive ants influence bees in the context of nectar foraging. First, we performed laboratory assays to assess the foraging behavior of bumble bees (Bombus impatiens) in response to live Argentine ants (Linepithema humile) or to a subset of ant chemical cues. We found that bees were deterred by the presence of live ants as well as the combination of olfactory and gustatory ant chemical cues. Next, we characterized specific ant-bee interactions and behavioral transitions at shared nectar resources. We found that two-thirds of bee behaviors did not involve feeding, and, of those, the majority of them were aggressive interactions with ants. Similarly, 70% of behavioral transitions did not involve feeding, of which 82.3% were transitions among aggressive behaviors. Consistent with predictions of interference competition, the number of ants at a shared resource decreased the probability of a bee feeding and increased the likelihood of a bee being bitten. Similarly, getting bitten by an ant decreased the probability that a bee would subsequently feed. Finally, we examined participation and foraging success of bees during experiments with live Argentine ants, as well as the influence of ant-bee interactions on bee foraging activity and movement. We found that the majority of bees never foraged during experimental trials, consistent with high levels of non-activity in other social insects. There was further evidence of foraging specialization among bees: foragers that came into contact with ants and were nonaggressive were less successful at resource acquisition, while the foragers exhibiting aggression toward ants were more successful.