Sleeping aggregations of the bee Idiomelissodes duplocincta (Cockerell) (Hymenoptera : Anthophorini) and their possible function

Males of the bee Idiomelissodes duplocincta roost in the evening together o n the stems of desert shrubs during months in central Arizona. The size of the aggregation can vary greatly during the few days to several months when a shrub is being used as a sleeping site. Some males return to the same pl ant for up to two weeks but show little site fidelity ta a particular stem. When frequently-occupied stems are experimentally cut and moved to new sit es in a shrub and replaced with other stems of similar dimensions, the bees rarely utilize: the replacement stems but instead shift elsewhere or seek out the previously popular stems In their new locations. This result sugges ts that odor cues applied by sleeping bees (or some other special propertie s of the favored stems) attract male bees coming to specific roost sites. S leeping aggregations are occasionally visited by a predator of the bees, th e assassin bug Apiomerus flaviventris. However, the number of assassin bugs present at any one aggregation on a given evening is small (not exceeding four in the present study), and few bees are taken. Sleeping bees do not at tack or harass the assassin bug. Moreover, they usually ignore approaching assassin bugs rather than flee, even when the predator vigorously attempts to subdue a neighboring bee on a sleeping stem. Thus, male bees in sleeping aggregations apparently gain anti-predator benefits largely through the di lution effect.