The Nesting Behavior of Dawson's Burrowing Bee, Amegilla dawsoni (Hymenoptera: Anthophorini), and the Production of Offspring of Different Sizes

Abstract

Females of Dawson's burrowing bees have a well-defined brood cell cycle involving cell construction, waxing, provisioning, egg laying, and cell capping. In one study population, nesting bees built smaller brood cells for offspring of lower weight and larger ones for heavier offspring, demonstrating their ability to anticipate the desired size of an offspring at the outset of a brood cell cycle. Furthermore, individual females varied the number of provisioning trips made per brood cell cycle by a factor of two or more, apparently exercising control over the amount of brood provisions supplied to an offspring. The size distribution of emerging males at two widely separated locations in 1997 was nearly identical to that recorded in 1995. These findings suggest that the production of small males (minors) is the result of active female control rather than the product of food shortages that force females to undersupply some brood cells. Female foraging decisions resulted in a bimodal distribution of weights of mature dormant larvae at one site in 1997. However, the times required to complete brood cell cycles at this site were not distributed bimodally. This result stemmed in part from daily variation among females in the duration of their provisioning trips as well as from seasonal variation in provisioning trip times. When provisioning trips lasted longer, females tended to make fewer trips per brood cell cycle, and so were presumably more likely to produce minor sons. As a result, the weight of an offspring was not tightly linked to the time investment required to produce it, making it difficult to compare the relative costs of minors and majors in terms of maternal time investments.