Orchard mason bee

The orchard mason bee, Osmia lignaria, is a megachilid bee that makes nests in reeds and natural holes, creating individual cells for their brood that are separated by mud dividers. They are unlike carpenter bees in that they cannot drill holes in wood. O. lignaria is a common species used for early spring fruit bloom in Japan and the United States, though a number of species of other Osmia are cultured for use in pollination.

Spring
The bees emerge from their cocoons in the spring when the daytime temperature reaches 14ºC (57ºF). The males emerge first. They remain near the nesting site and wait for the females to begin their emergence, which can be several days to weeks depending on the number of days of warm weather. The first thing the females do is mate. A female will typically mate once, maybe twice. She will be absent from the nesting site for several days while she feeds and waits for her ovaries to fully mature.

When a female is ready, she seeks out a suitable nest. O. lignaria females like to nest in narrow holes or tubes, though they have been found to nest inside cedar shakes and even keyholes. Beekeepers put out pre-made nesting materials to entice the females to stay close to the orchard. Rain, wind, and free-release (the practice of letting loose cocoons out rather than letting them emerge in their natal nests) discourage females from selecting a nesting site near their natal nest. A female might inspect several potential nests before settling in. Once she had found the right nest, she flies outside of the hole and does a in-flight dance. She is orienting on major visual features in order to find her nest when she returns from foraging.

O. lignaria arrange their nest as a series of partitions, with one egg per partition. She begins the process by collecting mud and building the back wall of the first partition. Then she makes trips to nearby flowers. Unlike honey bees which visit flowers that are miles away, she prefers flowers that are nearby the nest. She can visit 75 flowers per trip, and it takes 25 trips to create a complete pollen/nectar provision. She works tirelessly during the day, only stopping once the sun has gone down. When the sun rises the next morning, she will bask in its rays until she is warm enough to fly. Then she continues where ever she left off the day before.

Once the provision is complete, she backs into the hole and lays an egg on top of it. She collects more mud to seal off the partition. The new wall also doubles as the back wall of the next cell. She continues until she has filled the nest, leaving about an inch of space in front without any eggs to protect her brood from predators. O. lignara, like many insects, can select the gender of the egg they lay by fertilizing the egg, or not. Unfertilized eggs are males, while fertilized eggs are females. The adult bee lays female eggs in the back of the burrow, and the male eggs towards the front. She lays about three males to every one female.

When the egg hatches, the provision provides food for the larva as it goes through many changes on its way to becoming an adult. It will spend most of its life alone in this dark cell made by its mother.

Once the female has finished the nest, she plugs the entrance with one thick mud wall. Then she seeks out another location for a new nest. She works tirelessly until she dies. An O. lignaria female lives for about four to eight weeks and she can complete an average of four 6-inch tubes in her lifetime, with about eight eggs per tube. That's about 60,000 blossoms per bee. For this reason farmers have cultivated the insect for use in fruit orchards.

Summer
By the early summer, a larva has consumed all of its provisions and begins spinning a cocoon around itself and enters the pupal stage; the adult females die off as the season progresses.

Fall and Winter
The young bee is now a fully developed insect and hibernates inside its cocoon for the duration of the winter. They burn through their fat reserves to stay warm. If it stays cold for too long, the bees can die of starvation. Alternatively, if the temperature rises too fast, they may emerge before the blossom. Farmers are known to exploit their emergence cycle and time their release to coincide with the first orchard blossoms.

External link

 * Orchard Mason Bees Gardening in Western Washington
 * The New Mexico Native Bee Pollinator Project