Advantages and disadvantages of large colony size in a halictid bee: the queen's perspective

Abstract

The size of the group of social species might influence basic aspects of productivity and social interactions. In many primitively social insects, foundress queens are basically in control of the number of workers in their first brood. We examined factors that might influence the optimal number of workers a queen should produce during the solitary founding phase in Lasioglossum malachurum (Hymenoptera, Halictidae). A priori, it seems plausible that she should produce as many workers as possible (1) to maximize colony productivity and (2) to minimize the impact of brood parasitoids. However, there might also be unfavorable consequences of a large colony size from the queen's perspective. First, the queen might incur disproportionately high costs that decrease her potential for subsequent reproduction. Second, the queen might not be able to suppress the development of ovaries in a large number of workers. As a clear advantage of a large colony size, we found an increased production of sexuals. Contrary to our expectation, in the first worker phase, nests that were parasitized by Sphecodes bees had more workers than did unparasitized nests. We found no evidence that the production of the first worker brood entailed costs to the queen. However, the degree of development of worker ovaries increased with colony size, and some degree of development was detectable with as few as four workers. This study shows that the number of workers a queen produces might depend on the interaction of several factors, some of which have not been considered in detail yet.