Mealybugs are soft, waxy insects that feed on a wide variety of plants including grapes, trees, as well as indoor and and outdoor garden plants. They feed by piercing-sucking and can resemble soft scales, without the scale covering. Mealybugs produce large amounts of honeydew that usually attracts black sooty mold, and/or ants. They can be major pests on certain crops such as wine grapes in California, and are generally favored by warm weather and in areas without extreme winters or indoors.

Mealybug Identification

Mealybugs are in the family Pseudococcidae and are closely related to armored scales, soft scales and the cottony cushion scale. The bodies of mealybugs are distinctly segmented and mealybugs are usually covered in wax, with some species having waxy filaments around their bodies that can be used to distinguish species. Mealybugs are sometimes confused for other types of insects such as soft scales.

Adult mealybugs are usually observed as females which are wingless and look similar to nymphs. Adult male mealybugs have wings but are rarely seen. Many mealybug species can reproduce asexually, which allows large populations to grow very quickly. Mealybugs are usually found in colonies and can be found feeding on leaves, in plant crowns, on stems and some species feed on roots. Most mealybug species are not considered major pests but there are a few which are economically important.

Mealybug life cycle

Adult female mealybugs can lay between 100-200 or more eggs in a 10 to 20 day period. Eggs are laid in cottony sacs that may be attached to plant crowns, leaves, bark or fruit. Longtailed mealybug is an exception, because they produce eggs that remain with the female until egg hatch.

Mealybugs nymphs are sometimes called crawlers and are usually yellow, orange or pink. They do have wax covering at first, but begin to excrete wax once they begin feeding. Older nymphs are not as fast moving as younger nymphs. Mealybugs go through several instars before becoming adults.

Depending on the environment, mealybugs may have up to six generations in a year. In warm or indoor environments, their may be many overlapping generations in a single location. 

In some environments mealybugs may overwinter under bark as egg sacs or as first instar nymphs. This is the case in grapevines and some other orchard crops.

How to Use the Vine Mealybug Growing Degree Day Model

Mealybug Damage

Mealybugs are piercing-sucking insects that damage plants by sucking the phloem from the leaves, which can reduce plant vigor and decrease fruit quality. Mealybugs also produce sticky honeydew and wax which often coincides with black sooty mold, which also reduces plant vigor and fruit quality. On ornamental plants, mealybug colonies are unattractive. Depending on the plant, small populations of mealybugs may not result in significant damage, but higher populations can result in leaf drop. Root feeding mealybugs can cause plant decline and decreased vigor. These are not seen unless the plants are dug up and roots exposed.

Many perennial plants can be infested with mealybugs. They are an important pest on citrus and grapes, but can also infest stone or pome fruits. There are also many ornamental plants that may be damaged by mealybugs such as cacti, coral bells, figs, flax grasses, fuchsia, gardenias, hibiscus, jasmine, mimosa or oleander. The cypress bark mealybug can infest cypress, cedar and junipers. Indoor and greenhouse plant are very susceptible to mealybug damage, because they are less affected by cold weather and are less vulnerable to predators. African violet and gardenias are among the most commonly affected house plants. Herbs such as rosemary and sage can also be affected.

In some cases, such as on grapevines, mealybugs can transmit viruses which is a secondary risk on mealybug infestation.

Mealybug Management

Mealybugs can be very difficult to manage with insecticides alone. An integrated pest management program that combines several approaches is often need to prevent or manage mealybug infestations. There are many cultural practices that can reduce mealybug populations and biological control options. In some cases, chemical control may be needed, but there are precautions that may be used to maximize insecticide effectiveness.

Cultural Practices

Mealybugs are not very fast crawlers, and adult female mealybugs cannot fly. Because of this, the primary way that mealybugs are spread are through wind dispersal or through human interactions; on tools or farm equipment. In indoor settings, this is how mealybugs are introduced. By cleaning equipment, and carefully inspecting new plants, mealybugs may be controlled in indoor settings by preventing them from entering.

If mealybugs are found, infested plants may be removed or pruned to remove infested areas. Older plants tend to be more susceptible, so they should be removed periodically. Pots, stakes and other materials should be routinely inspected for mealybugs and egg sacs. High pressure water sprays may be successful in controlling small mealybug populations, but in most cases plants or materials should be removed.

Tender, green plant growth is more susceptible to mealybug damage, so avoiding overwatering or high nitrogen fertilization is important where there may be infestations.

Biological Control

Mealybugs have many natural enemies that can feed on them. If populations are low, these beneficial insects may be sufficient to keep mealybug populations at an acceptable level. There are several parasitic wasps that lay their eggs in or on mealybugs including species in the genera coccophagus, leptomastix, allotropa, pseudaphycus and acerophagus. Parasitoid activity can be observed by pupae within mealybug colonies or by mealybug “mummies” with emergence holes. Leptomastic dactylopii is sold commercially and is an option for release in greenhouses or citrus groves to control citrus mealybugs.

Natural predators include lady beetles green and brown lacewings, spiders, minute pirate bugs and predaceous midge larvae. Some of these are available commercially, or may be attracted with flowering plants. Broad spectrum insecticides can damage these populations.

The mealybug destroyer lady beetle a common commercially available option, however it is not able to overwinter so it usually can only establish successfully in warmer climates. It is often released in citrus orchards or greenhouses after a cold winter may have killed off naturally established populations. Mealybug destroyer lady beetles are red and black and larvae are covered in white wax which makes them resemble mealybugs. Mealybug destroyer lady beetles should be released when there is an abundance of mealybug egg sacs, because they need to feed on eggs to stimulate their own reproduction. Mealybug destroyer lady beetles can be reared with mealybugs in jars on potatoes or other plant material. Sticky petroleum smeared around the top of the jars prevent the mealybugs from leaving, but still allow the lady beetles to fly out and into the field or greenhouse. 

Ants can feed on mealybug produced honeydew and will protect mealybugs from natural enemies, so ant control should be a priority when mealybugs are also present.

Chemical Treatment

Treating mealybugs with insecticides can be challenging for two reasons: their waxy covering can repel many insecticides and also they usually hide under bark, in plant crowns or in other regions that are hard to reach with traditional spraying methods. For greenhouses and house plants, spot treatments are recommended. A 70% or less solution of rubbing alcohol in water can be used to kill small infestations of mealybugs. It can be applied with cotton swabs to spot treat problem areas. If too much alcohol is used it can burn the leaves, and more water may be needed to further dilute the solution. Rubbing alcohol may also be applied with a spray bottle, but a much smaller dilution 10-20% should be used.

In agricultural or field settings, insecticidal soaps, or oils can be used to suppress mealybug populations. They will be more successful against nymphs that have not yet developed the waxy covering, and may have toxicity to the plant if not applied properly. Dinotefuran is an active ingredient that is systemic and may be used on some landscape plants. Neonicotinoid are usually less reliable against mealybugs than other piercing sucking insects and can damage natural predator populations. Pyrethroids also may be labelled but can damage natural predator populations as well and should be used with caution.

After applying any insecticide, plants will need to be monitored and assessed for mealybug control. Repeat treatments may be needed, or severely infested plants may be need to be removed altogether.

References:

Bettiga, L. J. (editor). 2013. Grape Pest Management. UCANR Publication 3343. Richmond, CA. (See chapters 37-42 for information on mealybugs on grapes).

Dreistadt, S. H. 2016. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, 3rd edition. UC ANR Publication 3359, Oakland, CA.

Godfrey, K. E., K. M. Daane, W. J. Bentley, R. J. Gill, and R. Malakar-Kuenen. 2002. Mealybugs in California Vineyards. UCANR Publication 21612, Oakland, CA.