page_title: Megachile rotundata
section_title: Colony cycle
hierarchical_section_title: Megachile rotundata / Colony cycle
caption_attribution_description: Comparison between (A) a female modern leafcutter bee (Megachile rotundata) and (B) LACMRLP 388E (Megachile gentilis) male and in order to display obvious similarity in general morphology at pupal stage.
context_page_description: Megachile rotundata, the alfalfa leafcutting bee, is a European bee that has been introduced to various regions around the world. As a solitary bee species, it does not build colonies or store honey, but is a very efficient pollinator of alfalfa, carrots, other vegetables and some fruits. Because of this, farmers often use M. rotundata as a pollination aid by distributing M. rotundata prepupae around their crops. Each female will construct and provision her own nest, which is built in old trees or log tunnels. Being a leafcutter bee, these nests are lined with cut leaves. These bees feed on pollen and nectar and display sexual dimorphism. This species has been known to bite and sting, however it poses no overall danger unless it is threatened or harmed and its sting has been described as half as painful as a honey bee's.
context_section_description: As a member of the Hymenoptera order, this bee is haplodiploid. Adults emerge by the end of the summer through one of two developmental pathways: larvae will develop by the end of one summer and proceed through the a pre-pupal diapause phase until the next summer or larvae, known as "second-generation" bees, will skip this phase and emerge as adults in the same summer.
  The larva transitions through four instar stages before emerging as an adult. During its development, which occurs rapidly, the larva consumes the pollen ball and enters diapause when the pollen is fully consumed. In its progression into the diapause phase, the larva will defecate pellets in a ring formation and then spins its cocoon out of silk threads. The next spring, the mature larva pupates, a process that lasts 3–4 weeks, and completes its development. Once the bee is developed, it cuts its way out from the nest by chewing itself out of its cocoon.
  Upon emergence, females will mate immediately and begin constructing their nests after one week.
  Progeny released via the two alternative pathways for emergence display different sex ratios as well as sizes. Among adults who emerge during the summer of the same year, the sex-ratio is biased towards males. Among the "second-generation bees," however, the sex ratio is female biased. Further, spring-emergent adults weigh more than summer-emergent ("second-generation") adults. These differences have been proposed to be attributed to the chances of survival to mating of the two sexes and the metabolic costs involved in development. Bees that undergo diapause and emerge in the spring must endure the long winter, and thus require more food stores. As a result, they will be larger when they mature. Another explanation has been that smaller bees mature faster and thus are able to mate more quickly when they emerge in the summer to avoid the cold, harsh conditions of the winter.
  The sex ratio of the offspring also depends on the distance between nesting and foraging sites. Females have been observed and determined to bias their offspring sex ratio to males at larger flight distances from the nest.
caption: Pupae of (A) female M. rotundata and (B) subfossil male Megachile gentilis
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