Rhododendron Borer
Adult -The rhododendron borer moth has a black head with green and white markings. The thorax is black and blue with a broad patch of pale yellow or shiny white on each side. The abdomen is also black and blue with segments two, four, and five trimmed with yellow dorsally; segments three through six are yellowish on the underside. The legs are yellow and white epically and dark basally with some light-colored markings. The wings are transparent with a rusty-black fringe and some yellow scales. There is a tuft of black and yellow scales at the tip of the abdomen. The female has broader bands on segments two, four, and five than the male does. The female's anal tuft is short and rounded, whereas the male's is fan shaped. One of the smallest members of the family of clearwing moths, this moth has a wingspan of 10 to 15 mm.
Larva -The yellow-white larvae are caterpillars about 13 mm long.
Host Plants -Rhododendron is the principal host for the rhododendron borer. Mountain laurel and azalea are also attacked.
Damage -Twigs and small branches are preferred by the rhododendron borer. Infested branches become weakened and may break off. Leaves on infested branches often turn brown. Occasionally older parts of the shrubs are attacked. The main trunk may have numerous holes with fine sawdust protruding from them. Past infestations on older plant parts will appear as shallow, longitudinal grooves in the bark.
Life History -Adults emerge from their pupation sites during May and June and deposit eggs on twigs. Newly hatched larvae bore into stems and dig long tunnels in the soft pith. The tunnels become filled with small, reddish fecal pellets and serve as sites for overwintering and spring pupation.
Pruning infested branches helps to control the rhododendron borer. For specific chemical controls, see the current state extension service recommendations.