An ecological study of Batesian mimicry in the British Syrphidae (Diptera)

Abstract

This thesis is concerned with Batesian mimicry in British Syrphidae (Diptera), and examines the question of whether the ifies gain protection from mimicry.
Batesian mimicry is the resemblance of a palatable animal (the mimic) to a distasteful or otherwise protected animal (the model), such that protection is gained by the mimic. Syrphidae (hoverflies) are colourfUl but defenceless insects which often resemble members of the Hymenoptera. This study provides evidence that certain species of hoverfly gain protection from their resemblance to Hymenoptera.
In collaboration with Liverpool Museum the British Syrphidae were matched by eye to presumed model Hymenoptera. Once presumed model/mimic pairs had been suggested, a comprehensive survey of three sites in the north west of England was undertaken during 1994. Each site was visited once a week and counts were made of all Syrphidae and Hymenoptera on three plots at each site. Mean frequencies of models and mimics were compared, and it was found that mimics usually occurred when.models were present, and models were usually more abundant than the mimics; the data were also analysed usingan analysis of variance, and it was found that for most species tested there was a significant covariance between the mimic and presumed model numbers.
Survey work in 1994 and 1995 showed that bumble bee mimics follow model rank order on each site, but not on all individual habitat plots. One aspect of fly behaviour of a bumble bee mimic was also studied (time spent feeding on flowers) and compared to other hoverifies and the presumed model. The results showed that the time the mimic spent on flowers was not the same as that of the presumed model.
In the quest to understand hoverfly predation, immunological techniques are developed to test wild bird blood for evidence of antibodies against hymenopteran venom. The theory is that birds which have learned though a nasty experience that a particular colour pattern is distastefUl will also avoid other similar patterns, i.e. Wa bird is stung by a wasp it may not predate a hoverfly resembling the wasp.
The main conclusion is that there are specific and non-specific mimics, and that nonspecific mimics significantly covary with model numbers, but specific mimics do not, which is not what one might have predicted if these hoverilies really do gain protection through Batesian mimicry. Also, it is possible to detect an immune response against wasp venom in birds and a method has been developed to embark on field trials in the future.