Answer: If you find large holes in your rose leaves, they're probably the work of caterpillars or leafcutter bees. If the holes are irregular and occur within the central portions of the leaves, or if entire leaves have been eaten, then your plants are plagued by caterpillars. Caterpillars are the larvae of butterflies or moths and they eat leaves for food. They can cause a great deal of damage to a growing plant. On the other hand, semicircular sections taken out of the edges of rose leaves are a sure sign of leafcutter bees. These half-inch insects don't eat the foliage they cut; instead, they use it to build their nests.
Caterpillars can be picked off by hand and destroyed. They can also be controlled using various chemical sprays. The organic alternative is to use Dipel or Thuricide (Bacillus thuringiensis), a bacterium fatal to caterpillars but perfectly safe for plants and other animals. No real treatment is necessary for leafcutter bees, although you might want to prune away the damaged leaves. Don't use insecticides on these particular bugs, since they aid in pollination.
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