Leafcutter Bees

Leafcutter Bees Leafcutter bees are important native insects of the western United States. They use cut leaf fragments to construct their nest cells. They often are essential pollinators of wild plants. Some leafcutter bees are even semidomesticated to help produce alfalfa seed. However, their habit of leaf cutting, as well as their nesting in soft wood or plant stems, often attracts attention and concern.

Leafcutting bees are mostly moderate-sized (around the size of a honey bee, ranging from 5 mm to 24 mm), stout-bodied, black bees. The females, except the parasitic Coelioxys, carry pollen on hairs on the underside of the abdomen rather than on the hind legs like other bees. When a bee is carrying pollen, the underside of the abdomen appears light yellow to deep gold in color.

Life Cycle :Leafcutter bees are solitary bees, meaning that they don’t produce colonies as do social insects. Instead individual female leafcutter bees do all the work of rearing. This includes digging out nesting areas, creating nest cells and providing their young with food. Adult females may live up to 2 months and lay some 35-40 eggs during this time.Leafcutter bees nest in soft, rotted wood, thick-stemmed pithy plants and in similar materials that the bees can easily cut through and excavate. Nest tunnels may extend several inches deep and coarse sawdust may be deposited at the entrance, sometimes causing confusion with other wood nesting insects such as carpenter ants. However, leafcutter bees restrict their tunneling to soft, rotted wood and do not cause damage to homes or other wooden structures.

There are also concerns about leafcutter bees nest that in canes of roses, excavating the pith of canes that have been pruned. Leafcutter bees will sometimes nest in the largest diameter rose canes, but cause little damage as they restricting tunneling to the pith and rarely girdle cambium. Furthermore, other insects, including various hunting wasps (Pemphredon species) and small carpenter bees far more commonly tunnel and nest in rose canes.After the nest has been produced, leafcutter bees collect fragments of leaves to construct individual nest cells. The bees cut leaves in a very distinctive manner, making a smooth semicircular cut about 3/4-in in diameter from the edge of leaves. Although many types of leaves will be cut, leafcutter bees will preferentially select certain types, notably rose, green ash, lilac, and Virginia creeper. This injury is often only a minor curiosity.

Damage: These insects are found world-wide and they all have the interesting habit of cutting pieces of leaf to use for lining their burrows.These bees seem to prefer certain landscape plants, but almost any broadleaf deciduous plant may be used. Cultivated roses, azalea, ash, redbud and seedling maple leaves are the plants that are used most commonly in urban and suburban landscapes.The adult female bees cut round to oval disks from the margins of plant leaves. The damage is considered a curiosity and nuisance since the plants are rarely damaged. However, ardent rose growers find the leaf damage unacceptable. In roses, more severe damage can be caused when the female bee burrows down the pith of larger canes that have been recently pruned. This burrowing may kill the cane back further than desired.

Control:Insecticides are ineffective for preventing leaf cutting. The only known control of leaf injuries is to cover susceptible plants with cheesecloth or other loose netting during periods when leafcutter bees are most active.Numbers of leafcutter bees in an area can be reduced if breeding sites are eliminated, although these might be difficult to detect. Look for rotting boards with sawdust pushed out of excavated tunnels or thick stemmed plants with hollowed openings.To prevent leafcutter bees from tunneling into rose canes, seal exposed pith as canes are pruned. This can be easily achieved by placing a thumb tack, bit of sealing wax or white glue on the opening.

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