BUMBLEBEE FORAGING PREFERENCES: DIFFERENCES BETWEEN SPECIES AND INDIVIDUALS

5 SUMMARY

A simple and reliable marking technique for bumblebees, requiring inexpensive and easily obtainable equipment, was tested and under good weather conditions was found to be adequate, with marks surviving for at least fourteen days, allowing individual bees to be recognised. It appeared to have little or no effect on the behaviour of the bumblebees, as many were re-sighted foraging naturally (TABLE 1). At the same time as marking the bees, a simple field method of measuring the functional proboscis length and head measurements was developed and used.

In the "bee walk" a transect up a lane between two fields (FIGURE 1) was walked at two hour intervals, eight times a day, for five days during each of the three sessions throughout the summer season of 1995. The presence of actively foraging individual bees was recorded to investigate the flower preferences of species, caste and individuals, and whether individual bees or species showed preferences in their choice of flowers.

A program for calculating flower preference of bumblebees seen during the bee walk was used for the species and castes concerned (FIGURES 4-7). It was felt that it truly reflected what had been seen in the field and demonstrated real inter-species preferences.

Tongue length, which differs between some bumblebee species, may partially account for species flower preference, but there appear to be other factors, some physiological, that also contribute to flower preference.

Individual marked bees recorded in the bee walk were found to prefer a subset of the species flower preferences (FIGURES 9-12). There are many suggestions why an individual bee chooses to major on a particular flower species, but insufficient data were available to test any of these suggestions here.

The constancy of bees followed while foraging was remarkably high (FIGURE 13), and was compared to that of marked individuals recorded in the bee walk. In all cases the constancy and flower preference over one foraging trip was a subset of the preferences shown by the individual during the bee walk.

A review of the literature showed that the term constancy is used very loosely, and consequently bumblebees have been regarded as relatively inconstant foragers. This is because there have been studies at a nest and species level, as well as at the level of the individual foraging trip. Constancy is important because it facilitates the passing of pollen from one flower to another of the same species by an animal visitor, leading to successful pollination, so it is suggested that "constancy" should be used when referring to a single foraging trip, and "preference" to the differential use of different flower species on anything more than one foraging trip.

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6 ACKNOWLEDGMENTS

John Alexander kindly gave me permission to work on his land.

Bundle, my dog, was very neglected during the August bee walk, but never complained, and was always cheerful and affectionate.

Dr.I.J. Patterson showed me how to enter the data for the Tukey Test and kindly helped me interpret it.

Gordon Smith constructed four nest boxes, lent me his ventimeter and vernier callipers, let me use his computer and printer, and showed me how to use his flatbed scanner, and was a constant source of support and encouragement throughout.

Dr.C.C. Wilcock gave me some much needed advice on flowers and introduced me to Knuth's marvellous books.

Dr.M.R. Young agreed to supervise this project, he gave lots of very good advice, most of which I took, and always encouraged me, especially when I thought everything was going wrong. His suggestions after the first draft were invaluable and greatly improved the finished work. All the semi-colons in this thesis would have stayed as commas, and half of the commas would be missing were it not for his skilful editing.

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7 REFERENCES

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Waser, N. M. (1986). Flower constancy: definition, cause, and measurement. The American Naturalist. 127: 593-603.

Willmer, P. G., Bataw, A. A. M. and Hughes, J. P. (1994). The superiority of bumblebees to honeybees as pollinators: insect visits to raspberry flowers. Ecological Entomology. 19: 271-284.

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(C) Copyright 1999 L. Smith