Leafcutter Bees and Those Missing Bits From Your Roses

The leafcutter bee is a solitary bee which along with mason bees and carder bees belongs to the family Megachilidae.This family of bees is notable for the fact that their pollen carrying apparatus (called a scopa) is restricted to the under surface of the abdomen, rather than mostly or exclusively on the hind legs as in other bee families.The leafcutter bee takes its name from its method of nest-building.As a solitary bee it does not live in a colony like the honey or bumble bee.The female is solely responsible for nest finding, building and the welfare of the next generation. However, it is not uncommon to find several in close proximity to one another. In fact in some parts of the world their territories can be quite extensive even covering several acres if the conditions are right. Leafcutter bees like mason bees, can cause damage to property depending upon their numbers and where they choose to build their nests.Life cycleIf you see neat segments cut out of the leaves of your roses or other shrubs, leafcutter bees are the likely culprits. Using their mandibles (mouthparts) they remove neat pieces of leaves or even flower petals in some instances, to construct and line their nests, overlapping the pieces collected to construct cigar-shaped cells in hollow spaces. They will nest in a variety of places, in the ground, under stones, in cavities in wood and stone, plant stems, and in dead wood. As many as 12 pieces of leaves are used by the leafcutter bee to form each cell. Smaller circular pieces of leaves are used to seal the cells and there are usually 6 to 10 cells per nest.Before sealing the cell the female bee deposits a supply of pollen and nectar, then lays an egg on top, seals it up and goes on to build the next one. Each cell can take the bee around 6 to 8 hours in total to complete and seal off. Once she has sealed the last cell and has laid all her eggs the leafcutter bee has done her job and dies.These bees are unusual in the insect world as each female lays on average only about 15 eggs. Compare that with a queen honey bee who can lay 100′s of thousands of eggs in her lifetime.The young over-winter in their cells as mature larvae and emerge as adult bees in late spring-early summer. The last egg laid is the first to hatch and these are usually males who then stay around on nearby flowers waiting for the females to emerge.PollinationLeaf cutter bees are considered to be very efficient pollinators and are being increasingly bred in the US and elsewhere as a substitute for failing honey bee colonies, in particular Megachile rotundata, the alfalfa leafcutter bee or lucerne leafcutter bee.This species was imported from Europe and has now been introduced into most major regions of the world, as it is an efficient pollinator of alfalfa, carrots and other vegetables.Originally imported into North America to pollinate alfalfa, which honeybees avoid as the flowers need to be pried open to reach the pollen, these bees have become widespread. The alfalfa leafcutter bee is now managed intensively in North America and has become a multi million dollar business. They are also widely used in Russia and New Zealand and Australia where alfalfa is known locally as Lucerne.It has been calculated that one alfalfa leafcutter bee can do the pollination job of 20 honey bees. As unlike honey bees they do not collect pollen in baskets on their legs but collect it in hairs on their abdomens and are therefore more likely to spread it about as they move around.StingsLeafcutter bees as with other solitary bees tend not to be as aggressive as honey bees and to a lesser extent bumble bees. Both the male and females are more likely to use their mandibles, however the female does have a stinger but will only use it if squeezed or caught beneath clothing. This bee’s sting is not as painful as a honey bee sting but is more like the bite of a mosquito in terms of pain level. Therefore unlike honey bees there is no necessity to wear bee suits when managing leafcutters.