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Sunday, May 25, 2014

Leafcutter Bee Perfect Circles Now Seen on Plants

Leafcutter bee damage to bottle tree.
Q. My recently planted Carolina jasmine vine and rose bush are being shredded by cutter bees!! I've been told there is no insecticide to kill or deter them. Is this so? Both of these plants are adjacent to other plants but the others are not affected. I'm at wits end seeing perfect circles in the leaves! Also, why would you WANT cutter bees?

A. Leafcutter bees can be pretty destructive to the appearance of many plants. They are pretty selective in the plants they choose. Other plants affected besides your Carolina jasmine and roses include bougainvillea, grape leaves, basil and other leafy herbs, photinia and ash leaves.
Leafcutter bee damage to grape leaves.
            Part of the female leafcutter bee’s life cycle is to cut circles out of soft, thin, smooth leaves and use them to build nests for their young. The nests are constructed of individual cells, each with a ball of nectar, pollen and one egg.
            They build these nests in cracks and crevices and holes that vary from about 1/4 inch to 3/8 inch across and deep enough to construct individual cells for their young. They also build nests in the stems of some pithy ornamentals like roses.
Leafcutter bee nesting box made from a solid block of wood with 3/8 holes drilled in it. Used to increase the population of leafcutter bees in a landscape. Putting soda straws in the holes and removing them in about March reduces the population of bees.
            A frequent recommendation among Rosarians is to seal pruning cuts in roses with Elmer’s glue, a safeguard against leafcutter bees nesting in rose canes.
            Leafcutter bees are important pollinators of commercial crops and were introduced into the United States from Europe. They have been used in Nevada for pollinating alfalfa primarily.
            The bee is slightly smaller than a honey bee and won’t sting unless highly provoked or injured. Because they are such prized pollinators of urban vegetable crops, I encourage people to live with the damage they create or drape affected plants with cheesecloth to keep them away.
            If you want to reduce their populations, another method to control damage, you can put out bee boxes, which are blocks of wood drilled with holes large enough to accommodate a portion of a soda straw. The females deposit their eggs inside the soda straws. You can dispose of the straws when they are full but before the young bees emerge.
            Using insecticides is highly discouraged and it doesn’t prevent the damage anyway.

1 comment:

  1. If you are going to dispose of their nests in the manner described, please go out of your way to ask if anyone wants them. Plenty of folks would love to have a nursery hatching and after the bees have left return your nesting site to you for the next year . . . . ask on the local gardening, urban farming and permaculture forums.