The hawthorn (or two-circuli) mealybug, Phenacoccus dearnessi, is present throughout Illinois but tends to be most noticeable in northern Illinois. This is not a major pest, but it is often very noticeable when the females cluster on branches, resembling popcorn.
Hawthorn mealybug overwinters as a second-instar nymph on the trunks or branches of hawthorn trees, Crataegus spp. In the spring, females, which are about 1/8 inch long, disperse to the base of buds. Females lay eggs that are covered with a white waxy covering. The eggs hatch into nymphs that feed on plant leaves during the summer. They use their piercing–sucking mouthparts to remove plant fluids. Heavy infestations of hawthorn mealybug can weaken plants and possibly cause severe defoliation. In addition, this mealybug is a heavy honeydew producer. Honeydew, which is a clear sticky liquid, is an excellent medium for black sooty mold fungi. In the fall, nymphs migrate back to the trunk and branches of hawthorn trees to overwinter.
Although hawthorn mealybug is not a major ornamental pest, under heavy infestations, management may be warranted. Pest control materials recommended for management of hawthorn mealybug include bifenthrin (Talstar), chlorpyrifos (Dursban), imidacloprid (Merit), insecticidal soap, and mala-thion. For best results, make applications when nymphs (crawlers) are present. There are natural enemies of hawthorn mealybug such as ladybird beetles. One species of ladybird beetle resembles the mealybug and feeds on the young and adult stages. The presence of natural enemies may provide enough control so that insecticide applications are not needed.