From the KSU Entomology Newsletter, article by Raymond Cloyd
We have received numerous inquiries regarding insects feeding on the leaves of rose plants. The insects are sawflies and there are at least two species that attack roses this time of year: the rose slug, Endelomyia aethiops, and the bristly rose slug, Cladius difformis. Rose sawflies are the immature or larval stage, which eventually become a black to yellow adult that resemble wasps. Rose sawfly females create openings or slits along the edges of rose leaves with their saw-like egg laying device (ovipositor) in which eggs are inserted. Larvae emerge (eclose) from the eggs and resemble small slugs. Larvae are approximately 1/2 of an inch long when full-grown and yellow-green, with an orange head.
The larvae will fall onto the soil surface to pupate. Rose sawflies overwinter as pupae in earthen cells created by the larvae. There is typically one generation per year in Kansas. Rose sawfly larvae cause damage by feeding on the underside of rose leaves causing the leaves to appear skeletonized.
Small infestations of rose sawflies are best dealt with by removing the larvae by hand and placing into a container of soapy water. A high pressure water spray will quickly dislodge sawfly larvae from rose plants. Once dislodged the larvae will not crawl back onto rose plants. There are contact insecticides containing various active ingredients that are effective in managing populations of sawflies. Sawflies are not caterpillars.
Consequently, the bacterium, Bacillus thuringiensis subsp. kurstaki, which is the active ingredient in various products (e.g. Dipel®) has no activity on sawflies because the insecticide is only effective against caterpillars.
