Leafcutter Bees
Females are said to be solitary nesters because they do not co-operate to make nests, and unlike honey bees there is no worker caste. However females like to make their nests in close proximity to other nesting females, so the species is said to be gregarious. This characteristic means that when bees emerge for the first time, most females will tend to nest back in the holes they emerged from or close by, so that nesting populations tend to persevere from year to year. The Life-Cycle of the Leafcutter Bee (Magachile Rotundata) The life cycle of leafcutting bees is quite different to that of honey bees. Leafcutting bees overwinter as hibernating fully-fed prepupae (= grubs), each in a cocoon surrounded by pieces of leaf. As temperatures rise in spring the prepupae gradually change into pupae and then into a male or female bee.
By about late October in warmer parts of the country the bees chew their way out, the sexes mate, and the females begin to search for blind-ended tunnels about 6 mm in diameter and 80-120 mm long in which to build new cells. After cleaning the tunnels of loose debris females then carry in about 8-10 oval pieces of soft, flexible leaf pieces to divide line and cap their brood cells. They cut the leaves with their scissor-like mandibles, making smooth, circular or oval cuts from the edges of leaves that are about 12mm in diameter. Just before she finishes cutting it, the female starts to beat her wings, so she is already flying by the time the leaf fragment is severed. How cool is that??
The leaf pieces are then cemented together with salivary secretions and leaf resins. (Some of their favorite leaves are Lucerne, lotus roses, green ash, lilac, red bud and Virginia creeper), but they don’t appear to be too choosy. Please don’t begrudge this housing material to these hard-working mothers! These missing leaf bits don’t damage the plant in any way.
The leaf pieces can be easily seen partly rolled up under the bodies of females as they enter their nesting tunnels. Once the cup is complete the females carry pollen in special hairs under their abdomen (the rear part of the body), into the nest tunnels, and the pollen is stored in the cup and is moistened with nectar.
Like the leaf pieces, the pollen is very visible as the females enter their tunnels. An egg is then laid on the stored pollen and nectar, and the cell is closed with several circular pieces of leaf. In sunny weather of about 20 degrees C or more, a female bee can make more than one cell a day, and in several weeks can fill a nest hole with 10-12 cells. She then may go on to make more cells in a second, and even a third nest hole.
Within a couple of days the eggs hatch to small larvae (= grubs) which set about to eat all the pollen and nectar within about a week, after which they each spin a cocoon around themselves. If the cells are made before about the end of December, the fully grown larvae may then develop straight into new bees which will emerge and re-nest that same summer, but if eggs are laid after the end of December, the great majority of progeny turn into the overwintering prepupae.
By about a few weeks after emerging the males have usually dispersed from the nesting site, but females will continue nesting until the end of March. Flowers favored by females are the small pea-flower-shaped types such as lucerne, lotus and clover, but they will also readily visit many others, for example daisy-types, and our native Carmichaelias (native brooms), and various species of Hebe. Females prefer to forage on flowers very close to nest sites, so they often can be seen on flowers in the home garden. However if suitable flowers are not available nearby, females will fly up to a kilometre to collect nectar and pollen.
However, not all females make cells that grow live prepupae because of perhaps a failure to lay eggs, and in addition there is a very small native parasitic wasp only 1 mm long that can kill larvae and overwintering prepupae. The result is that nest tunnels gradually become clogged with leaves and old cocoons, so best management practice is to take apart the nesting trays any time between April and May, and remove old nesting material, so that the females that emerge during the coming nesting season have clean tunnels in which to build new cells.
BeeGAP only promotes the use of wooden Nesting Tray Systems or Easy Tear Nesting Tubes as they allow you to examine each tunnel and check on the state of your Leafcutter bees and any other native bees that may have taken up residence. By removing the bee cocoons, you can remove all debris and mites that may be in the tunnel.
BeeGAP does not endorse drilled nesting holes in wood as these cannot be cleaned or inspected!
