CELL AND NEST CONSTRUCTION COSTS IN 2 CAVITY-NESTING BEES (OSMIA-LIGNARIA-PROPINQUA AND OSMIA-RIBIFLORIS-BIEDERMANNII) (HYMENOPTERA, MEGACHILIDAE)

Cell-partition and nest-plug material collecting and construction cost s are measured for two populations of two species of cavity-nesting be es (Osmia lignaria propinqua Cresson and Osmia ribifloris biedermannii Michener). Construction costs were = less for O. r. biedermannii usin g leaf material versus mud used by O. l. propinqua. The per-cell cost of collecting and construction indicates that nests of either species should contain four or more cells to equalize the cost of the nest plu g. These. collecting and construction costs must be combined with the pollen-nectar cost of offspring production if an accurate measure of p arental investment is expected.