any of a group of small, sap-sucking insects (order Homoptera) that are worldwide in distribution and attack citrus trees and ornamental plants, especially in interior plantscapes and greenhouses. Observed most frequently is the ovoid, sluggish mature female, about 1 cm (0.4 inch) long.

The name mealybug is descriptive of the insect's body, which is covered by a white sticky powder resembling cornmeal. The females and “crawlers,” or active young, cluster along the veins on the undersides of leaves. Males are active fliers and have only two wings. Common members of the Pseudococcidae are the citrus mealybug (Planococcus citri) and the citrophilus mealybug (Pseudococcus calceolariae). Biological control and insecticidal soaps, horticultural oils, and traditional insecticides have been effective against these pests.

Mealybugs are related to scales, whiteflies, and aphids.