Mealybugs

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Nick Thorp
Lead author: Nick Thorp

Species


Mealybugs belong to the order Homoptera and the family Pseudococcidae. Several different species of mealybug exist including citrus mealybugs, longtailed mealybugs, root mealybugs, pink hibiscus mealybugs, grape mealybugs, Mexican mealybug, papaya mealybugs., and banana mealybugs.

Host/Site


Mealybugs are found outdoors on fruit trees such as apples, pears, citrus, apricots and grapes, and ornamental shrubs and trees. They are a common pest of indoor plants. Ground mealybugs of the genus Rhizoecus injure roots and can be found on fruits and grasses.

Identification


Appearance
Adult female mealybugs are soft-shelled, oval shaped insects from 1.5 to 3 mm long. They have many distinct segments, and are usually coated with a white, waxy substance. Ground mealybugs do not secrete the same cottony wax of other species.


Photo Courtesy of Eugene Nelson

Indicators
A mealybug infestation is indicated by large amounts of cottony wax, typically at the base of indoor plants, or among leaves and fruit in outdoor plants. The wax created by mealybugs also attracts a black, sooty mold, which is unsightly and difficult to wash off of fruit. Large infestation will stunt growth, cause leaf shedding, or even kill plants.

Life Cycle


Females deposit over 500 eggs within the cottony wax. After laying the eggs the females die. Within a week the nymphs, also known as crawlers, will hatch. They will then migrate over the plant to find a suitable place for sucking sap from it and remain in that stage for 2-6 weeks. Male nymphs develop into winged adults, while female nymphs develop into the oval shaped insects described above.

Natural Enemies


There are several natural enemies that may already be in your garden that prey on mealybugs. See Biological Controls for information on what insects will best suit your situation.

Monitoring


Inspect all new plants for bugs, and physically remove or kill them before bringing the plants indoors. Mealybugs typically feed in leaf and stem axil, where the leaves connect to the stem, as well as on the roots. Check these areas on a regular basis for the presence of mealybugs. Often the presence of numerous ants near the bottom of plant stems indicates that there is a mealybug infestation.

Action Threshold


Act immediately when you see mealybugs or signs of mealybug damage on your plants.
In larger gardens, complete eradication of mealybugs is not typically possible.

Physical/Mechanical Controls


Remove mealybugs from plants when they are first detected. This can be done by spraying leaves with water, using a wet cloth to rub mealybugs off, or, if there are large populations, pruning infected branches and leaves off. Immediately dispose of clipped plant pieces to prevent mealybugs from infesting the same plant again.

A cotton swab soaked in rubbing alcohol can be applied directly to visible mealybugs to kill them. Alcohol, an organic solvent, will dissolve the wax around the insects and their egg masses, killing them.

Insecticidal soaps and horticultural oils containing potassium salts or fatty acids such as that produced by Safer Inc. can be used to reduce mealybug populations before a natural enemy is introduced, to treat infestations that have not responded to other controls, or as a soil drench for soil mealybugs.

The key to management of an infestation is catching the problem early. If mealybugs are found on only a few plants it may be worth destroying these plants to avoid further infestation in the garden.

Biological Controls


Lady Beetles are natural predators. One species, the mealybug destroyer (Cryptolaemus montrouzieri) is a particularly effective predator in areas without harsh winters.

Parasitic Wasps can be effective controls. In particular, Leptomastix dactylopii is an effective control for the citrus mealybug.

Green Lacewings are also a natural predator of mealybugs.

All three of these beneficial insects are available for purchase through a number of online distributors. Be sure to follow all handling and release instructions from the vendor.

Ant management can also be an effective biological control. Mealybugs produce a sweet, syrupy substance called honeydew that ants eat. Ants will protect mealybugs from other natural enemies in order to encourage production of honeydew.

Chemical Controls


Not recommended.

References


Flint, Mary Louise. Pests of the Garden and Small Farm. Berkeley: University of California Press, 1990.

Olkowski, William, Sheila Daar and Helga Olkowski. Common-Sense Pest Control: Least-Toxic Solutions for Your Home, Garden, Pets, and Community. Newtown, CT: Taunton Press, 1991.

Pundt, Leanne. "Managing Mealybugs in the Greenhouse." University of Connecticut Integrated Pest Management Program. 25 June 2008. <http://www.hort.uconn.edu/Ipm/greenhs/htms/mealybugs.htm>.

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