Mealybugs

Sternorrhyncha: Pseudococcidae

Mealybugs are found in all zoogeographical regions, mainly in the tropics, but often extend into the temperate regions.

Host plants and damage

Many species like the striped mealybug, Ferrisia virgata Cockerell are highly polyphagous, attacking plant species belonging to more than 150 genera in 70 families. Among the hosts of economic importance are cauliflower, soybean, tomato, mango, avocado, and pigeon pea.

Mealybugs feed on all plant tissues (especially leaves and fruits) by piercing plant surfaces and sucking plant sap. Some species are specialized on leaves; others are found below the soil surface and feed on roots.

The citrus mealybug has a toxin in its saliva which causes its host plants to drop leaves and buds. Affected parts turn yellow and dry up. A by-product of mealybug feeding is sticky honeydew, which covers infested foliage.

Many mealybugs vector diseases, e.g. F. virgata vectors the cocoa swollen shoot virus (CSSV) and cocoa trinidad virus (CTV).

Morphology & biology

Mealybugs are soft, oval or pear shaped, flat, segmented insects, often covered with a white, mealy wax. The most common species have a pinkish body that is visible through the wax cover.

Very few mealybugs give birth to live offspring. Most species produce several hundreds of eggs enclosed within an egg sac. The egg sac is composed of waxy secretions from the female. The egg hatches in five to ten days, or longer until conditions are favorable. Most nymphs molt 3-4 times. Adults have glossy white wax threads extend from the body. Some species have long wax tails, which can be used to distinguish them. However, many species are morphologically very similar and cannot be distinguished in the field. Slide-mounted preparations are needed for correct identification.

Like scale insects, mealybugs have often a symbiotic relationship with ants. They provide food to the ants through their excreta (honey dew). In return ants offer protection and distribute the pest to different parts of the host plant. The honey dew promotes sooty mold. Female mealybugs have no wings and can travel only short distances by crawling. The main dispersal stage of mealybugs is the first instar, which may be natural dispersed by animals and wind.

Monitoring

Most mealybugs avoid direct sunshine and bright light. Look for infestations around terminal shoots, on undersides of leaves, and fruits. Colonies are sucking plant sap, which results in yellowing and drying.

Pest management

Treatment is only required if infestations become severe. in most cases healthy plants can withstand some infestations by meralybugs without loss of fitness.

Biological control

In Hawaii the mealybug F. virgata is successfully controlled by the coccinellid Cryptolaemus montrouzieri.

Cultural control

At the beginning of a local outbreak infested branches should be cut and destroyed.

Chemical Control

Many synthetic insecticides are reported to be effective. However, some mealybug species have developed resistances against different classes of insecticides. Synthetic insecticides have to reach the mealybug, which is because of the wax cover sometimes difficult. Treatments may have to be repeated since new mealybugs hatch from egg masses which might have been missed by the spray.

Spraying fine horticultural oils or insecticidal soaps, covering mealybugs, can be used for control.

All insecticide applications should coincidence with the appearance of the crawlers (first instar). This is when the insect is most vulnerable to materials applied.