The sun dance: Evidence for density induced behavioral plasticity in Bembix americana spinolae (Hymenoptera: Crabronidae)

The task of mate location by solitary and communally nesting male Hymenoptera can be daunting. Often, the nests and nesting areas are cryptic, and females rarely advertise their location and sexual receptivity. To overcome these obstacles, males my employ a number of behavioral strategies; most attention in the literature has been given to males that secure and defend territories. In this study, however, we compared the strategies employed by large and small males within the same aggregation of Bembix americana spinolae (Hymenoptera: Crabronidae). This aggregation is called the “sun dance”, and is presumably used as a form of scramble competition. We compared the amount of time spent in rest and the number of male-male contacts required to displace a male from rest between large and small individuals. We also compared the behaviors of large and small males in large and small aggregations. Finally, we morphometrically compared what we considered to be large and small males to insure that there was a difference in size between large and small morphs. We found that 4 of the 5 morphometric indices supported our assessment of large and small males. We also found that large males spend significantly more time in rest and require more male-male contacts to be displaced than do small males in large aggregations. Finally, we found that there is no difference in behaviors between size morphs in small aggregations.