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The biology and ethology of Osmia nigrifrons are described and contrasted with O. integra, O. unca, and O. nigrobarbata. The nesting season begins in mid spring and extends about 45 days. Floral records for the species indicate a preference for papilionaceous legumes. Mud nests occur in tubular burrows and in sheltered sites. Nests are composed of from one to several hundred urn-shaped cells. Cells vary between different nest types but possess several constant features: (1) narrowed entry; (2) spiral cell cap structure; (3) constancy of inner dimensions; (4) construction of only soil. Mating, sleeping, cell construction and provisioning behaviour are described.Eggs deposited on top of the pollen-nectar mass required 11·7 days to develop. Larval feeding time averaged 28 days and then the cocoon is spun. Pupation begins in early September and the bee overwinters as adults encased in cocoons.Four years analysis of mortality factors is provided for one population. Mortality rates vary from a low of 31·2% to a high of 59·3%. Four hymenopterous parasites were reared from O. nigrifrons and one, Stelis chlorocyanea, was responsible for from 16% to 43% of the yearly losses.

AbstractA device designed to measure amount of pesticide solutions consumed by three species of bees (Megachile rotundata(F.), alfalfa leafcutting bee; Nomia melanderiCockerell, alkali bee; and Apis melliferaL, honey bee) is described in detail. Isolated bees fed freely from capillary tubes filled with known mixtures of pesticides and honey solutions. The change in volume of solution was used in determining the exact amount of pesticide consumed by each individual.