NESTING PREFERENCES OF THE SOLITARY BEE OSMIA-SANRAFAELAE (HYMENOPTERA, MEGACHILIDAE)

A series of cage studies was used to investigate nesting preferences o f Osmia sanrafaelae Parker. Bees preferred nest holes of smaller diame ter ill blocks ill the southwest corner of cages. Within multiple-bloc k arrays, nests were more frequent in the lower left corner. The numbe r of cells per nest was lowest in cages with the few est nests in some experiments, but did not vary in others. Nest diameter affected neith er the proportion of females produced per nest, nor the size of offspr ing of either sex. Rather, nesting females constructed cells of varyin g orientations within nests of different diameters, a process that res ulted ill approximately equal cell volumes. In one experiment, tile se s ratio of bees released within cages was varied and influenced tile s es ratio of offspring. Nests within cages in which a higher ratio of m ales to females was released contained a higher proportion of female o ffspring.