Praying mantis egg cases are very common this spring. Most are squarish masses that appear to made out of brown styrofoam laid on the stems of flowers, trees, and other plants. They range from about 1/2 to 1 inch across. Adult Chinese mantises laid these egg cases last fall. In late spring, each case will produce about 100 hatchling mantises, each about 1/4 inch long. These mantises are not native but are the common species sold to gardeners for placing in the garden to feed on pests. As a result, they have become widespread in Illinois. As biological control agents, they are a mixed blessing because they feed on anything they can overpower, eating beneficial as well as harmful insects. In fact, many hatchlings will be eaten by their brothers and sisters.
Gypsy moth eggs hatch when saucer magnolia (Magnolia soulangeana) drops its petals, which will happen in a couple of weeks in northern Illinois. However, with oak being a major host for this insect and being a tree that breaks bud later in the spring, delay treatment for this insect until the leaves have expanded enough to catch insecticide spray droplets. Bacillus thuringiensis kurstaki (sold as Dipel, Thuricide), spinosad (Conserve), tebufenozide (Mimic)—as well as other insecticides—are effective against the larvae. Arborists, landscapers, and others should feel free to treat infestations in Lake, Cook, DuPage, and McHenry counties; but collect specimens or photograph larvae in counties other than Lake so infestations can be verified by the Illinois Department of Agriculture in Des Plaines, (847)294-4343.
European pine sawfly larvae are appearing as grayish to greenish wormlike larvae on mugo, Scotch, and other pines in southern Illinois. Realize that these are not caterpillars and not susceptible to Bacillus thuringiensis kurstaki. Permethrin (sold as Astro), carbaryl (sold as Sevin), and other insecticides are effective. Because the larvae feed in groups, small infestations can be removed by hand.
Spruce spider mites can be treated now in southern and central Illinois. Verify the presence of this and other conifer-feeding mites by beating foliage over a white piece of paper. The grayish green mites will be knocked onto the paper, where they can be easily seen. Fast-moving red mites are predatory, and treat-ment may not be needed if they are numerous. Plant-feeding mites streak green when smashed; predatory mites streak red. Bifenthrin (sold as Talstar), insecticidal soap, and summer spray oil are effective against spider mites. Spray weekly, two or three times.
Hemlock rust mites are active throughout the state. These mites cause whitish to yellow stippling on the foliage. Heavy infestations result in yellowing and dropping foliage. These are eriophyid mites—so tiny that they are invisible to the unaided eye. Miticides as just listed for spruce spider mite are effective.
Cooley spruce gall adelgid and eastern spruce gall adelgid are susceptible to insecticides until saucer magnolia buds open. Only in parts of northern Illinois will these insects still be susceptible to insecticidal control efforts.