By Donald R. Lewis
Iowa State University
Houseplants are prone to a varied assortment of insect pest problems. Some of the most common are scale insects and spider mites. However, one of the easiest to recognize is the mealybug.
You’ve probably seen mealybugs at one time or another on the stems or leaves of a houseplant. They look like small white puffs of cotton or fluffy deposits of white powder. They are common on African violets, Ficus, jade gardenia, poinsettia and other indoor plants.
The body of each mealybug is oval and about 1/4 inch long. However, the soft, segmented body is concealed by filaments of white wax that cover the insect. The filaments extend out from the periphery of the body and may be up to 1/2 inch long.
Mealybugs are related to aphids and scale insects. Like these, the mealybugs feed on the plant’s sap by extracting it through a long slender beak pierced into the plant tissue. Heavily infested plants are weakened from excessive sap loss and may die. Lightly infested plants may only be stunted, yellowed or malformed. The sweet honeydew excreted by these sap feeders provides a substrate for the distracting black fungus called sooty mold.
The mealybugs found on houseplants lay eggs in a compact, white waxy sac, usually in the axils where the leaves join stems. Three hundred or more yellowish or orange eggs may be deposited by a single female. The eggs hatch into tiny, immature mealybugs called nymphs that move about on the plant searching for a place to settle and eventually insert their beaks into the plant and begin sucking out the sap.
As mealybugs feed numerous waxy filaments start forming as white, threadlike projections located along the edge of the body. The filaments grow, curl and tangle until the entire body is covered. Mealybugs usually remain in one place for their entire life span of four to ten weeks.
Mealybugs may be difficult to control and unless the plant is particularly valuable, it may be best to throw away infested plants before the insects spread to other houseplants. The standard, well-known remedies for houseplant pests are often successful if applied with diligence and persistence. Picking off individual mealybugs and egg sacs or dabbing each one with an alcohol-soaked cotton swab may be satisfactory for lightly-infested plants. Similarly, syringing the plants with a forceful spray of lukewarm water may adequately dislodge a light pest infestation.
Insecticide sprays are available for mealybugs and other houseplant pests. Use aerosol or hand pump spray products made just for houseplants. These may contain any of several different ingredients, including insecticidal soaps, pyrethrin, neem, or a synthetic pyrethroid such as permethrin, bifenthrin or resmethrin. Granular insecticides that you add to the soil of infested houseplants may be effective. Use with caution and read and follow all label directions.
Biological control is often used to keep mealybug populations at low levels on large houseplants grown in malls and botanical centers. A specific ladybug called the mealybug destroyer is particularly effective. These ladybugs, originally from Australia, are mass-produced by several companies in the U.S. The predators are purchased from the suppliers and released onto infested plants at regular intervals. The ladybug adults and larvae feed on the mealybug eggs and small nymphs.
A very tiny wasp that parasitizes mealybugs is also sometimes used to supplement control by the predators. As attractive as this option seems, it is unlikely to be practical for homeowners with a few, relatively small plants or with a limited infestation of mealybugs.
Additional information on mealybugs and other common, houseplant pests is available in pamphlet PM 1595, Houseplant Insect Control. Check at your local county extension offices or online at https://www.extension.iastate.edu/store/ListItems.aspx?Keyword=1595