Are droneflies batesian mimics of honeybees?

Abstract

This thesis explores the presumed Batesian mimicry of honeybees (Apis mellifera) (Hymenoptera:Apidae) by droneflies (Eristalis species) (Diptera:Syrphidae). Because droneflies do not show particularly close morphological similarity to honeybees, apart possibly in their size, the work has mainly concentrated on aspects of behaviour which may enhance their mimicry.
Analysis of model:mimic ratios revealed that dronefly and honeybee numbers were not consistent with what might be expected if Batesian mimicry was operating. It is suggested that droneflies, which out number their models, may still gain protection by adopting a safety in numbers strategy; they could enhance their mimicry by appearing to forage in small groups, like their honeybee models.
On a range of flowers it was found that droneflies behaved in a more similar way to honeybees than to other more closely related flies and bumblebees; they spent similar times on flowers and took similar times to fly between them. This was difficult to explain other than in terms of mimicry and suggests that dronefly behaviour may be evolving to be more like that of their honeybee models than other hoverflies. Further work explored this behaviour in more detail. Analysis of flight behaviour showed unexpected similarities between the dronefly Eristalis tenax and the honeybee in the flight speed, time spent hovering and routes taken between flowers. Analysis of pollen in faeces indicated that the pollen diets of droneflies were more similar to those of honeybees than to other hoverflies and suggested that further research may show that
droneflies are flower constant, like their honeybee models.
Having established that droneflies employ behavioural strategies to enhance their mimicry of honeybees, the work moved on to try and establish whether the mimicry enabled them to gain protection from their major predators, which are thought to be
birds. It was found that dunnocks, robins, great tits and coal tits discriminate in their prey choice when offered dead droneflies and honeybees along with other flies.
However, only dunnocks avoided both models and mimics but ate the other insects. More research is needed to fully establish the effectiveness of the mimicry. Finally, the effectiveness of the mimicry of a honeybee, social wasp and bumblebee by their hoverfly mimics was tested on humans using a questionnaire and coloured photographs. It was established that, in general, students could not distinguish between models and mimics but also found that many students would be prepared to kill hoverflies which looked like stinging insects. This raises serious conservation issues for hoverflies.
Overall, the findings of the work are consistent with the theory that droneflies are Batesian mimics of honeybees and that they employ behavioural strategies to enhance their mimicry. It also establishes that the mimicry is effective for humans and some birds.