Leafcutter Bees – Holes in Roses

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Leafcutter Bees – Holes in Roses

By George Giltner, Advanced Master Gardener

leaf cutting bee 1

A leaf cutter bee in action on a rose. Photo: itsnature.org

The rose enthusiast may recognize nearly circular, up to ¾ inch holes in rose leaves and petals that are cut at first glance, by what appears to be a fly.  The bug may also be observed going into pruned, thick rose piths.  Wait! Put down the bug spray.  This may be the leafcutter bee, a solitary beneficial bee.

leaf cutting bee 2

The leaf cutting bee has large jaws or mandibles. Photo: D. Almquist and David Serrano

Leafcutter bees can be identified by their stout, black bodies with light bands on the abdomen.  Pollen is not transported on the legs like typical honey bees. Instead the underside of the abdomen has thick, yellow hairs (scopa) for carrying pollen. The size is varies from 1/5 inch to one inch depending on which of the 60+ species is viewed.  Also note that flies have two wings, but bees have four.

The value of these bees is as with honey bees, they are important pollinators of fruits (blueberries, etc.), vegetables (onions, carrots, etc.), and many wildflowers.  Alfalfa and blueberry crops are commercially pollenated with Osmia species.

leaf cutting bee 3

Nesting house for Leaf cutting Bees. Photo: US Forest Service, Beatriz Moisset

Leafcutter bees are literally “holed up” nesters.  They make their nests in cylinder cavities, by excavating in rotten wood to soil to straw cavities (rose piths).  A bee house can be made for the garden by drilling bee-sized holes in driftwood.  The nest will occupy several inches of depth with a sawdust or leaf plug at the entrance.  Multiple egg cells are laid in the leaf-lined tunnels, each packed with a larval food supply of pollen and nectar. A single female will lay up to 40 eggs in its two-month life span.

 

Roses seem to be the preferred broadleaf for constructing nests, however green ash, lilac, Virginia creeper, azaleas, redbud, crepe myrtle bougainvillea and other plants with smooth thin leaves are also used by leaf-cutting bees.

 

If the leaf-cutting is a problem, the recommended control is to simply lay cover cloth over your prize ornamentals.  Normally, the leaf damage is minimal, and the value of this important pollinator compensates for its cut-out leaf circles.

 

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