Synanthedon rhododendri

The rhododendron borer is a tiny, native clearwing moth. Adult moth emergence may begin in May and last through July, depending upon local temperatures. Adult males are metallic black in color with narrow yellow bands across the abdomen on the second, fourth, and fifth abdominal segments, and a yellow line on each side of the abdomen. Wings are transparent. Females are very similiar in appearance, although the yellow bands are broader and cover the undersides of the abdomen as well (Beutenmueller, 1909). After mating, adult females lay their eggs (up to 40 each) near locations of the host plant with defects or injury - particularly, branch crotches, pruning cuts, scars, or old larval feeding galleries. Eggs are tucked into these areas by the females, who perish shortly thereafter. Larvae hatch and chew their way to the inner bark, where they tunnel and feed and fill these tunnels with small, reddish frass pellets. By late fall, the larvae move to the sapwood to overwinter. Feeding by rhododendron borer caterpillars begins again the following spring around mid-March as temperatures begin to warm. It is at this time the caterpillar chews more holes in the outer bark, pushing out more frass that may be noticeable to the observer. Oblong cells are created in the bark by early May, within which the mature caterpillars prepare to pupate. At maturity, caterpillars are up to 1/2 inch in length, whitish yellow in color, with brown heads. A woodchip and frass covered cocoon is formed at this time. Once ready to emerge, the pupa wiggles through a hole in the cocoon and the in the bark, leaving the pupal shed skin stuck halfway out of the host plant as the adult, wasplike moth emerges. A single generation occurs per year.