Several species of mealybugs pose problems for gardeners across North America. Host plants include citrus, apples, peaches, grapes, potatoes, and a number of tropical plants -- including houseplants. These tiny insects appear in clusters on the undersides of leaves and clumped in the forks of twigs and branches where they suck plant juices. As they feed, some species inject toxins that damage plant tissues.
Mealybugs are oval in shape, with a grainy, dusty looking surface that is actually a protective waxy coating. Large clumps of mealybugs may resemble fur or lint attached to a plant. Symptoms of their presence include yellowing leaves and dark, dirty patches on leaves, which is actually sooty mold growing on the sweet mealybug excretion called honeydew.
In regions without freezing winters, mealybugs are present year round. In colder climates, there may be 2 to 3 generations per year. The pests overwinter as eggs in cottony egg sacs or as tiny nymphs (the juvenile stage, commonly called crawlers).
Controls include insecticidal soap and horticultural oil. Natural enemies include the mealybug destroyer (a kind of ladybug), lacewings, and mealybug parasite (a tiny wasp).
Photography by Peggy Greb, USDA Agricultural Research Service, Bugwood.org