Q: My azaleas suddenly started losing their leaves. I saw some small, green things that look like caterpillars on the branches, but after spraying them with Bacillus thuringiensis, they are still alive and well. The azaleas are large and thickly clustered, so I can't reach back into the branches where they are. What can I do?

A: It sounds like you have azalea sawflies. There are many species of sawflies, and they affect many kinds of plants. I often find them on pine trees. Sawflies are voracious insects. They stick together in small groups and can defoliate a whole branch. They often only eat the old leaves or needles on a branch and leave the new growth alone. Two generations of sawflies can be produced in a year. The second generation may devour this year's new growth of leaves and needles, leaving the branch bare and possibly killing it.

The larva looks like a caterpillar. Larvae tend to stay in groups on a branch, but they don't create webs like many moth caterpillars. If you move your hand near a group of larvae, they may all throw their heads back at the same time. It is entertaining to watch.

The adult sawfly looks like a fly, but may have yellow and black stripes, making it look like a small bee or wasp. They are in the same overall insect group as bees and wasps. The female uses a saw-like apparatus to deposit eggs into a leaf or stem of a plant.

Bacillus bacteria insecticide won't work on sawflies. Try using an insecticidal soap or neem oil. Also, handpicking the larvae off the branches, whacking a branch in a bucket of soapy water, or giving the branch a really strong blast of a hose can work, if you can get close enough.

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

A: Leaf cutter bees are the culprits. A leaf cutter bee is a small bee that lays its eggs in solitary cells. It doesn't belong to a colony. They make holes in soft, rotting wood or hollow stems of plants to function as the egg cells. Then, they line the individual holes with round leaf cutouts. Wasps leave a paralyzed insect in the cell with the egg, but the leaf cutter bee leaves pollen and nectar in the cell for the larva. In colder climates, the larva remains in the nest over winter and hatches in spring. In warm climates, there can be three generations of leaf cutter bees in a year.

You can place a variety of small pipes and straws in a bundle, and the bees may use them as nest sites. They may also lay eggs in wooden boards that have holes drilled into them. The holes can be a quarter inch in diameter and several inches long. In California and Colorado, leaf cutter bees are used to pollinate alfalfa fields. In commercial operations, 4-inch thick plastic foam boards are used to collect the cocoons, which are taken to the fields.

Leaf cutter bees are beneficial and are great pollinators. 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.

Email questions to Jeff Rugg at [email protected]. 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.