Sorghum Webworm, Celama sorghiella (Riley)

PLANTS ATTACKED: The preferred hosts of the sorghum webworm are grain sorghums in general, but they attack seed of broomcorn, Sudangrass and Johnsongrass, and probably native grasses.

DESCRIPTION: The moth is small and whitish, with a wing expanse of about 1/2 inch. The forewings are irregularly mottled with yellow and brown. The hind wings are white.

Larva. The larva is more or less flattened, yellowish or greenish and marked with four longitudinal reddish to black dorsal stripes. Densely spaced spines and long hairs cover the body. The mature larva is about 1/2 inch long.

LIFE HISTORY: The insect hibernates in the larval stage on the host plant. At the advent of cold weather, the larvae leave the sorghum grain head and crawl down the stalk to protected areas behind leaf sheaths which envelop portions of the stalk. These worms pupate the following spring and emerge as moths about 1 week later. They are active primarily at night and deposit their eggs singly on the flowering parts or seed of the host plant. A female lays 100 to 300 eggs which are white with a pale tinge when laid but soon change to yellow or brown. Eggs hatch in 3 to 6 days. The larvae mature in about 2 weeks. There may be as many as six generations annually.

DAMAGE: The larva begins to feed almost immediately following emergence from the egg. It gnaws circular holes through the outer tissues of the grain, and then feeds on the starchy contents of the seed which usually is only partly consumed. One larva has been observed to consume the greater part of more than a dozen seed within a 24-hour period. The worm does not spin a web but when disturbed or dislodged from the grain head, it often will suspend itself by a finely spun silken thread on which it sways to and fro. Heavy infestations of these worms destroy most of the grain of a sorghum head. Heavily damaged grain heads contain large masses of fecal material excreted by the larvae.

BIOLOGY: Moths are active at night and live about 5 days. Females lay about 100 eggs singly, securely fastening them to the flowering parts or kernels of sorghum. Eggs are less than 1 /32 inch in diameter. They are white at first but turn deep yellow to brown before hatching in 3 to 4 days. A generation requires about a month. Larvae diapause on the host plant. The sorghum webworm occurs primarily in the more humid areas of eastern and southern Texas.