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.

[6] In North America, the species was deliberately imported to assist in the pollination of food crops, but has now become feral and widespread.

[14][15] Females construct tubular nests in a variety of sites, including rotting wood, flower stems, reeds, and soda straws.

When managed for pollination, the females are induced to nest in paper cylinders similar to drinking straws or drilled blocks of wood.

Each cell is made from circular disks cut from plant leaves using the bee's mandibles, hence the name "leafcutter".

With respect to sex ratios, larger cell provisions are correlated with a greater production of female offspring.

When these olfactory cues were experimentally removed, females of M. rotundata were unable to identify their own nests, revealing the importance of these chemicals.

In its progression into the diapause phase, the larva defecates pellets in a ring formation and then spins its cocoon out of silk threads.

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, so require more food stores.

Another explanation has been that smaller bees mature faster, thus are able to mate more quickly when they emerge in the summer to avoid the cold, harsh conditions of the winter.

Females have been observed and determined to bias their offspring sex ratio to males at larger flight distances from the nest.

[10] Research on second-generation bees illustrates that kin recognition of nest mates is not a genetically based behavior.

Further, fratricide has been hypothesized to be a nondiscriminatory behavior; emerging individuals treat developing siblings and non-siblings similarly.

When delayed for longer periods of times, however, emerging individuals would use their mandibles to destroy the cells of their nest mates.

[23] Megachile rotundata can feed on nectar and pollen from a variety of plants[24] but prefer Medicago sativa.

[5] Currently, 28 species are known to prey on M. rotundata, all of which have unique ways of invading and destroying their host nests.

Some species include Pteromalus venustus, Monodontomerus obscurus, Melittobia chalybii, Diachys confusus,[3] and Sapyga pumila.

[4] The most formidable predator of this species is P. venustus, a parasitoid wasp in which the female uses her ovipositor to sting a developing M. rotundata larvae or pupae.

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.

[26] 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.

[26] In controlling chalkbrood, such methods as decontamination of nest cells and materials and shelters was initially achieved using household bleach.

[3] Female alfalfa leafcutter bees have stingers, but both sexes usually use their mandibles as a defensive mechanism, usually only defending themselves when squeezed or antagonized.

[5] In managing M. rotundata for pollination, such methods as dichlorvos pest strips and ultraviolet lamps placed above liquid traps are effective in killing parasitoids, but not harming M.

[28] Megachile rotundata was accidentally introduced into the United States during the 1940s, and its management as a pollinator leads to increases in seed production of some crops in the U.S.

It has been shown to pollinate these plant species:[4] Such behaviors as gregarious nesting, use of leaves and nesting materials that have been mass-produced by humans, efficient pollination of M. sativa, and synchronous emergence of adult bees during alfalfa blooming period provide positive benefits for the use of these bees in agricultural development.