Interactions Among Syrphid Flies and Bumblebees on Flowers

E-ISSN： 1939-9170|62|1|81-88

ISSN： 0012-9658

Source： Ecology, Vol.62, Iss.1, 1981-02, pp. : 81-88

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Abstract

Interactions among bumblebees (Bombus terricola and B. vagans Smith) and small syrphid flies (Melanostoma mellinum L. and Toxomerus marginatus [Say]) were studied on pasture rose (Rosa carolina L.). Dominance interactions took the form: bumblebees > Melanostoma > Toxomerus. In the absence of bumblebees, Melanostoma foraged 41% longer, but the bees only reduced Toxomerus' foraging about 4%. The difference in bumblebee impact on the two syrphids resulted from Toxomerus rapidly returning after visits by bumblebees, while Melanostoma did not. Toxomerus used flowers most frequently when Melanostoma were not in them. Bumblebee foraging patterns appeared unaffected by either syrphid fly. Melanostoma may have a considerably greater impact than bumblebees on Toxomerus; a 14% reduction in foraging by Toxomerus was recorded in one test. This was because Melanostoma occupied flowers for several minutes at a time, while bumblebee visits lasted only several seconds. By affecting Melanostoma's activity, bumblebees inadvertently favored Toxomerus, because the latter returned quickly to flowers after bee visits; Melanostoma did not.