at foraging sites. Specifically, female N. lutea will lay their eggs on flowers and, when a bee arrives at this flower during provisioning, will secure itself, as a triungulin stage, to the bee. The triungulin will then, upon the host bee's arrival to its nest, remove itself from the bee, entering a cell and consuming all the provisions gathered by the host female. Mating Males of the species may, presumably by mistake, attempt to mate with other bee species that are using the same foraging areas as female leaf cutters. They follow several inches behind their intended partner, whether a leaf cutter or bumble bee, which is moving around a plant seeking a flower; then when the target does alight, the male leaf cutter darts rapidly onto the target's back. This causes bumble bees and nonreceptive female leaf cutters to move to another flower and in the process shed the male leaf cutter. The male may then move right to the next prospect, or may first stop for a sip of nectar. Disease Chalkbrood disease in M. rotundata, specifically larvae, was discovered in 1974 in Nevada. This disease occurs from exposure of M. rotundata to Ascosphaera aggregata, which is introduced into the nest cells through nectar and pollen provisions that females bring back from foraging visits. Signs of chalkbrood infection have been observed to occur in the fifth-instar larvae, leading to the milky appearance of the larval hemolymph and development of a pink, tan, or gray cast in their head or abdominal regions. These changes are accompanied by the spread of pink, tan, or gray color throughout the body of the larvae, and dark-colored, fungal cysts appear under the cuticle. A variety of microorganisms have been isolated from the alimentary canals and frass of M. rotundata. Bacteria include Bacillus firmus, B. licheniformis, B. megaterium, B. pumilus, and Streptomyces spp., and fungi include Trichosporonoides megachiliensis. With respect to the development of chalkbrood, the bacteria and fungi may promote the inhabitation of A. aggregata. This is supported by observations in chalkbrood-diseased larvae, which contain higher levels of bacteria and fungi in their guts than in healthy larvae. In controlling chalkbrood, such methods as decontamination of nest cells and materials and shelters was initially achieved using household bleach. Current methods include paraformaldehyde fumigation. Defense Female alfalfa leafcutter bees have stingers, but both sexes usually use their mandibles as a defensive mechanism, usually only