Whitemarked tussock moth, Orgyia leucostigma, eggs have hatched throughout most of Illinois, and the lar-vae (caterpillars) are chomping away. Their wide host range includes apple, birch, crabapple, elm, fir, hick-ory, horsechestnut, linden, maple, oak, pecan, poplar, rose, sycamore, and walnut.

Female moths are gray, wingless, hairy, and about 1-1/2 inch long. Male moths are brown and winged. The female lays 100 to 300 eggs in a frothy white mass, normally placed on the cocoon. In late spring, eggs hatch into caterpillars that quickly migrate to leaves. The young caterpillars skeletonize leaves–whereas older ones consume the entire foliage, leav-ing only the main vein and petiole. Full-grown cater-pillars are 1-1/2 inch long, with a red-to-orange head and a yellowish, hairy body. A black stripe runs down the middle of the back, bordered by a yellow line. Four tufts of hairs protrude from the first abdominal segment. Two long, black hairs project like horns in the front and one in the rear. Pupation occurs in a gray, hairy cocoon that is generally located in twigs and branches. This moth overwinters in the egg stage, and there are two generations in Illinois.

Whitemarked tussock moth may be managed by pruning out infestations or using a pest-control mater-ial when caterpillars are small, usually in mid-June or when mock orange and beauty bush are in bloom. Pest-control materials recommended are azadirachtin (Azatin/Ornazin), Bacillus thuringiensis kurstaki (Dipel, Thuricide), carbaryl (Sevin), cyfluthrin (Tempo), and spinosad (Conserve).

Natural enemies of whitemarked tussock moth include both parasitoids and predators, but they don't cause enough mortality to impact the population dynamics of the insect.