Gardeners become concerned when they notice tunnels in their rose canes or small, sparse, yellow or wilted rose leaves. These conditions are caused by insects which aren’t always a detriment to the garden. The most common tunnelers are hunting wasps that, for the most part, are beneficial predators. These small, harmless wasps nest in the rose piths but do not injure the plants. These hunting wasps feed on aphids and provide some degree of insect control.
Female wasps lay eggs on cut canes. The eggs hatch into caterpillars which tunnel into the cane pith. They feed for about two weeks on aphids brought to the nest by the female wasp. After two weeks, the larva goes into a dormant state before emerging as an adult wasp.
If the wasps do significant damage to a plant, prune the rose cane below the wasp nest area where there may be a slight swelling. Seal this cut (and routine pruning cuts) with water-insoluble glue or nail polish to prevent more nests of eggs. Controlling aphids may also encourage wasps to search for other nesting sites that have a reliable food source.