Leafcutter bees
If your rose leaves have smooth, semicircular pieces missing from the edges, as though cut with a hole punch, a leafcutter bee did it. The female cuts the pieces to line the cells of her nest, and she eats none of the leaf. These are solitary bees and useful pollinators. UC IPM says they should not be killed and that there are no effective controls. The RHS says the damage does not usually affect the plant's vigour. You do not need to do anything.
At a glance
- Kind
- Wild solitary bee — pollinator
- Size
- About honeybee size, darker, pale abdominal bands
- The tell
- Female carries pollen on a brush of hairs under the abdomen
- Cut
- Smooth semicircle, about ¾ in (19 mm) across, from the leaf edge
- Active
- Late spring to late summer; into early autumn in warm regions
- Sting
- Only if handled; very mild
- Control needed
- None
How it works
Leafcutter bees belong to the genus Megachile. Each female works alone. She finds a narrow cavity, such as a hollow or pithy stem, soft rotted wood, a gap in a wall or a tube in a bee hotel, and builds a row of thimble-shaped cells in it from pieces of leaf. NC State Extension notes that she uses round pieces for the base of each cell and oval pieces for the walls, and that a cavity holds eight or nine cells, each about half an inch long. Every cell is stocked with pollen and nectar and gets an egg. The young bee develops inside; the last brood of the season overwinters in its cocoon as a prepupa and emerges the following year.
This is why the cuts are so tidy. The bee slices out a smooth semicircle about ¾ inch across, rolls it up, and flies it back to the nest. Colorado State lists rose, green ash, lilac and Virginia creeper as favourites, but many other kinds of leaf are cut. A female may live up to two months and lay 35 to 40 eggs, and North Carolina sees at least three generations a year. Leafcutter bees carry pollen on a brush of hairs under the abdomen, and NC State calls them superior pollinators of hard-to-pollinate crops such as apples and legumes. One species, the alfalfa leafcutting bee, is managed commercially to pollinate alfalfa grown for seed.
What it is confused with
The leaf damage is what people notice, and several rose pests also leave holes. The shape of the damage tells you which it is.
- PestRose slug sawfly damage — The larva grazes one surface and leaves the veins, so the leaf goes see-through in windows before holes appear. It does not make a clean cut from the edge.
- PestJapanese beetle damage — Metallic green and copper beetles feed on the tissue between the major veins until the leaf looks like lace.
- PestCaterpillar or earwig feeding — Ragged, irregular holes and edges. A leafcutter's cut is smooth-edged and uniform in size, and none of the leaf is eaten.
- Also goodHoneybee — Much the same size. A leafcutter is darker, with pale bands across the abdomen, and the female carries pollen on a brush of hairs under her abdomen.
How to keep it around
Leafcutter bees need two things: flowers for pollen and nectar, and somewhere to nest. Most gardens already have both. If you would like more of them, or would rather they cut something other than your prize roses, do this:
- Leave some hollow and pithy stems standing through the winter; the bees nest in them
- Put up a bee hotel with narrow tubes, or leave soft, rotting wood in a quiet corner
- Grow a spread of open flowers from late spring to late summer, when the bees are flying
- If one rose must stay unmarked, cover it with cheesecloth or loose netting while the bees are most active; Colorado State says this is the only known way to prevent the cuts
- Seal the pith of rose canes after pruning if you do not want bees nesting in them
- Do not spray insecticides on plants in flower where bees are feeding
Pesticide sensitivity
These are bees. Any insecticide sprayed on open flowers can kill them, and no spray stops the leaf cutting anyway, because the bee does not eat the leaf. Open the compatibility matrix →
When to choose something else
There is nothing to control here. Look for a different cause if:
- The holes are ragged or run through the middle of the leaf — check for earwigs at night or caterpillars by day
- The leaf is see-through in patches before it holes — that is the rose slug sawfly, and a strong spray of water knocks the larvae off
- The leaf is lacy between the veins and there are metallic beetles on the blooms — see Japanese beetle
- You are not sure what is making the holes — start at holes in rose leaves