Honey bees avoid ant harassment using scent cues

The popular managed honey bee (Apis mellifera) provides pollination services in agricultural systems during crop bloom, However, when crops are not in bloom, these bees must sustain themselves and support their diet with floral resources from the natural and semi-natural environment. In Southern California, floral resources are typically limited in the early winter (January-early February), and presently, these floral resources are further limited due to the severe drought the state currently faces (2014). Drought adapted succulents, such as aloe (Aloe spp.) can provide critical early season floral resources to bees during this time. However, other organisms may be competing with and restricting floral access by bees, which are important pollinators.

Here we ask if the invasive Argentine ant (Linepithema humile) can restrict honey bee access to aloe plants and by which mechanisms. We conducted a two-part study that examined: 1) bee visitation rate and bee visitation duration to aloe flowers with and without ants, and 2) bee visitation to aloe flowers without the presence of ants, but with and without ant scent.

In our first study, we found that bees visit all flowers equally (where a visit is the sum of rejections and acceptances), but that bees prefer to accept (land on) flowers without ants present. When bees do accept the flower, the visit duration is longer on flowers without ants than with ants. The bee is only able to acquire nectar and pollen resources when it has fully landed on the flower, and is likely to acquire more resources during a longer visit. Our results suggest that bees may be harassed by ants and rejectconcurrently occupying flowers with ants present, and that the presence of the invasive ants limits resource acquisition by the bees.

In our second study, we found that acceptance rate is reduced on flowers with ant scent compared to scented or hexane scented flowers in the absence of any ants present. This suggests that bees learn to avoid flower with ants using the ant scent as a cue and can therefore avoid ant harassment. However, the implications are that the invasive Argentine ant can limit honey bee access to a vital resource during a critical early-season period.