Red-Twig Dogwood Caterpillars

Identification

• The red-twig dogwood (Cornus sanguinea) is also commonly referred to as the "winter flame." This is in reference to the scarlet twigs that envelop the bush in winter, making it a bright, showy specimen that provides significant color during drab, winter months. While it generally has few pests that bother it, the red-twig dogwood is susceptible to infestation from the dogwood sawfly (Macremphytus tarsatus), an insect whose larvae look like hairless caterpillars.

Dogwood Sawfly

• The larvae of the dogwood sawfly affect all plants of the Cornus species. The adult sawfly is similar to a wasp, while the immature insect is covered in a white, powdery substance and changes colors several times as it grows. The mature larva is covered with a collection of black spots on a cream-colored body. All stages of the larvae are vigorous feeders and quickly skeletonize the leaves of a red-twig dogwood, leaving the plant bare by late summer.

Management

• The larvae reach up to 1 inch in length and are hatched from a collection of 100 eggs deposited by the adult sawfly between May and July. Chemical control of dogwood sawfly larvae is effective if it is applied before the insects reach full maturity. At that point, they stop feeding and begin preparing the cocoons that will serve as shelter while they transform into adults. Insecticide is not beneficial once the larvae have entered their protective cocoons.

Considerations

• Only one generation of the dogwood sawfly occurs annually, with the larvae overwintering in wood holes before emerging as adults in the spring. Although they cause serious defoliation of the plant, their feeding is seldom damaging enough to threaten the overall health of the dogwood tree. However, the loss of leaves does stress the red-twig dogwood, making it more susceptible to the development of serious diseases, such as canker. Because of its large size, the insect is easily hand-picked from the dogwood.