Gypsy moth larvae are getting large enough to be noticed in northeastern Illinois. They appear as dark, hairy caterpillars feeding at the top of host trees. The caterpillars feed in groups but do not live in a silk tent. The Illinois Department of Agriculture finished the first of two larval gypsy moth sprays on leading-edge infestations in the “Slow the Spread” program during the last week of May. The second application will be later this month. They do not treat many infestations behind this leading edge, meaning that arborists and landscapers in Lake, Cook, DuPage, and McHenry counties that have not been treated are likely to find infestations.|
Trees that are commonly attacked include oak, poplar, aspen, willow, crabapple, apple, hawthorn, gray birch, river birch, paper birch, white pine, blue spruce, American beech, linden, serviceberry, sweet gum, witch hazel, hazelnut, and mountain ash. Many other trees and shrubs may be attacked as well. Trees unlikely to be attacked are ash, yellow poplar, sycamore, northern catalpa, honey locust, black locust, horsechestnut, dogwood, eastern red cedar, juniper, yew, lilac, rhododendron, azalea, arborvitae, and viburnum.
Conventional insecticides that are effective against gypsy moth caterpillars include carbaryl (Sevin), acephate (Orthene), and cyfluthrin (Tempo). The insect-growth regulators diflubenzuron (Dimilin), tebufenozide (Mimic), and azadirachtin (Neemix) are also effective. These insecticides mimic insect hormones, causing a hormonal imbalance within the insect that eventually leads to death. Because humans and other mammals, as well as wildlife, have different hormone systems, they are not susceptible to these materials. The bacterium Bacillus thuringiensis kurstaki (Btk) affects only the larval stages of insects and is very effective against gypsy moth caterpillars. It is sold as Dipel, Thuricide, and many other brands.