Leaf-Cutter Bees Place Eggs in Leaf Holes by Jeff Rugg on Creators.com

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Leaf-Cutter Bees Place Eggs in Leaf Holes

Q: I have noticed that several of the plants in my garden, from trees to rose bushes, have half-inch diameter holes missing out of the leaves. The holes are much larger than anything I have seen before. They don't have discolored edges like a disease, and I can't find any insects on the plants. What could be causing this?

A: Leaf-cutter bees are your culprits. It is a small bee that lays its eggs in solitary cells. It doesn't have a colony. They line the individual holes, where the eggs are placed, with the round cutout of the leaf. The hole is made in soft-rotting wood or hollow plant stems. Many bees and wasps leave a paralyzed insect in the cell with the egg, but the leaf-cutter bee leaves pollen and nectar for the larva. In colder climates, the larva remains in the nest over the winter and hatches in the spring. In warm climates, there can be three generations in a year.

You can place a variety of small pipes and straws in a bundle, which they may use as nesting sites. They also use boards that have hole drilled into them. The holes can be 1/4 inch in diameter and several inches long. In California and Colorado, leaf-cutter bees are used to pollinate alfalfa fields. Nest material of 4-inch thick Styrofoam boards is used to collect the cocoons that are taken to the fields.

Leaf-cutter bees are beneficial and do a lot of pollinating.

It is worth a few holes in rose leaves to have such an interesting insect in the yard. Don't try to get rid of them.

Q: My azaleas have suddenly started losing their leaves. I saw some small green of caterpillars on them, but after spraying them with Bacillus thuringiensis, they are still alive and well. The azaleas are large and thickly clustered, so I can't get into the branches to find the caterpillars. What can I do?

A: It sounds like you have one of the azalea sawflies. These are voracious insects. They stick together in small groups and can defoliate a whole branch.

Since they are not the larval stage of a moth or butterfly, the Bacillus bacteria insecticide won't work. Try using insecticidal soap or Neem oil. Also, handpicking and a really strong blast of a hose can work, if you can get close enough.

The adult is a non-stinging small wasp. There is only one generation each year. If they have not done too much damage, you can leave them alone.

E-mail questions to Jeff Rugg, University of Illinois Extension at jrugg@illinois.edu. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.