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There are a number of species of mealybugs that can affect plants, although the citrus mealybug and the long-tailed mealybug are probably the most common. Mealybugs are sap-sucking pests that infest plants in colonies, usually on protected parts of the plant such as the leaf axis or under peeling bark. Adult females are around 4mm in length, pancake-shaped and greyish pink in colour. However, they appear white since they secrete powdery wax over their bodies and around the feeding areas. Eggs are laid into the wax. Young mealybugs look very similar to the adult females but are extremely small.
Mealybugs feed on the plant sap. Large infestations can weaken plants and cause leaves to drop. Excess sap is excreted as honeydew which promotes the growth of sooty moulds over the leaves.
Always inspect newly acquired plants for mealybug wax before placing them next to other plants within a house or greenhouse. This will resemble small pieces of cotton wool and could contain eggs even if the adult mealybugs are not present. Remove the wax and keep the plant away from other plants until you are sure it is no longer infested.
The small predatory beetle Cryptolaemus montrouzieri is commercially available and can be released onto infested plants where it will eat both adult mealybugs and their eggs. A parasitic wasp Leptomastix dactylopi is also available for mealybug control. As a last resort, organic products containing fatty acids or plant oils/extracts are also available from garden suppliers. These will need to be applied following the label instructions.
Regular vacuuming around infested plants will help to prevent the mobile juveniles from spreading to other locations. Juveniles can also be carried to new locations on clothing and hands.