Found in warmer growing climates, mealybugs are soft-bodied, wingless insects that often appear as white cottony masses on the leaves, stems and fruit of plants, especially citrus. They feed by inserting long sucking mouthparts, called stylets, into plants and drawing sap out of the tissue.
Damage is not often significant at low pest levels. However, at higher numbers they can cause leaf yellowing and curling as the plant weakens. Feeding is usually accompanied by honeydew, which makes the plant sticky, encourages the growth of sooty moulds and can cause ant problems. Ants may also transport mealybugs from one plant to another.
During monsoon season they often appear on ornamental hibiscus. Mealybugs seem to prefer humid conditions and can be a problem in areas planted on heavier soils or with large or closely planted trees with a lot of shading.
Mealybugs get their common name from white waxy secretions that cover their bodies. They are in the order Homoptera, which includes scales, whiteflies, and aphids, some species of which also cover their bodies with white waxy secretions, making field identification confusing. In warmer climates like the Arizona desert, mealybugs are serious pests on many citrus and ornamental plants. Don’t confuse mealybugs with woolly aphids.
Adults (1/10 — 1/4 inch long) are soft, oval distinctly segmented insects that are usually covered with a white or gray mealy wax. Small nymphs, called crawlers, are light yellow and free of wax. They are active early on, but move little once a suitable feeding site is found.
- Prevent new infestations. Examine, quarantine for two to three weeks, and treat as necessary (see below) all new plants before placing them near mealybug-free plants. Examine all plants frequently for pests.
- Conserve natural enemies. Predatory insects such as lacewings, ladybugs, and several small parasitic wasps prey on outdoor mealybugs and can help keep their population to a minimum. Avoid unnecessary insecticide use to minimize damage to these beneficial insects.
- Remove mealybugs manually. Depending on host plant size and scope of infestation, remove mealybugs with alcohol-dipped cotton swabs or physically knock them off plants with a forceful water spray and repeat as necessary. While unlikely to eliminate mealybugs, this approach can often keep the infestation within tolerable limits and will have no negative impact on beneficial insects.
- Control ants. Ants are known to transport mealybugs from one plant to another, so physical barriers or chemical controls that do not adversely impact beneficial insects can be part of a prevention and control program.
- Use insecticidal soap or superior horticulture oil sprays. If above methods fail to reduce mealybug populations to acceptable levels, use insecticidal soap sprays or superior horticultural oil spray following label directions carefully to avoid damage to sensitive plants and beneficial insects. If possible, treat when crawlers are present. Mealybugs hide under leaves and in crotches, so be sure spraying is thorough. Repeat application as necessary in accordance with label instructions.
Sources: University of Arizona, Missouri Botanical Garden; University of California, Davis, IPM