Mealybugs can be serious and persistent pests in the greenhouse. Well-established infestations are difficult to control because their waxy secretions help to protect the young nymphs and eggs from penetration with chemical sprays.
Mealybugs are soft-bodied insects that are covered with a whitish wax. With their piercing-sucking mouthparts, they feed in leaf and stem axils and even on the roots of some plants. There are a number of different mealybugs of concern to greenhouse growers including the citrus mealybug, longtailed mealybug and root mealybug. Recently, the pink hibiscus mealybug, papaya mealybug, banana mealybug and Mexican mealybug have been introduced into the US.
Identification and Biology
Mealybugs are soft-bodied insects, from 1/8 to 1/4 inch long that are covered with white waxy secretions. Their life cycle consists of an egg stage (except for the longtailed mealybug that gives birth to live young), immature stages ("crawlers") and adult. The immature crawlers mature in about 6 weeks to 2 months. Mature females die after egg laying. In the greenhouse, continuous and overlapping generations make control difficult.
Citrus Mealybug on Mandevilla
Citrus Mealybugs (Planococcus citri) females are small (less than 1/8 of an inch long), mealybugs with a faint gray stripe running down their back. They also have short waxy filaments around the margin of their oval body with a slightly longer pair of filaments at their rear. Females produce a cotton-like egg sac containing yellow eggs and lay from 300 to 600 eggs. Eggs hatch into small, active crawlers. When the crawlers settle down to feed, they begin to secrete wax and produce honeydew. Males resemble females from the egg stage to the 3rd instar nymphal stage. After pupating, the winged adult male emerges but only lives for 1 or 2 days and does not feed.
Longtailed Mealybugs (Pseudococcus longispinus) - also have a well-defined stripe running down their back. However, longtailed mealybugs have distinctive long tails (about ¾ or more of their body length) hence their common name. Longtailed mealybugs produce live young and do not produce an ovisac.
Pink Hibiscus Mealybugs (Maconellicoccus hirsutus) Adult females are wingless, about 1/8 of an inch long, and pinkish in color with a reddish-pink body fluid. Eggs and crawlers are pinkish as well and may be covered with a white, waxy material. Pink hibiscus mealybug occurs in the tropics and subtropics and was recently found in Florida.
Signs of Root Mealybug Infestation are shown on the right.
photos by Leanne Pundt, Extension Educator, University of Connecticut
Root Mealybugs (Rhizoecus spp) feed on the root systems of plants so can be undetected for long periods of time. Infected plants become wilted and stunted. Look on the edge of the root ball for the white, oval shaped (1/16 to 3/16 of an inch long) mealybugs that look like they have been covered by flour. Root mealybugs are slow moving, sac-like mealybugs with pronounced crosswise grooves. They do not have filaments surrounding their body like many of the foliar feeding mealybugs. Once established in the greenhouse, root mealybugs may spread as crawlers from plant to plant as the water moves out of the drainage holes to nearby plants and in plant debris.
Mealybugs are piercing sucking insects that remove the sap from plants. As they feed, leaves turn yellow and drop. New growth may become distorted. Honeydew supports the growth of black sooty mold fungus. If high enough populations develop, plants can be killed.
Once mealybugs become established, it is difficult to achieve effective control. So, prevention is the grower's first line of defense. Inspect incoming plants for signs of mealybugs. Inspect roots of newly purchased plants for the root mealybug. Do not hold over "pet plants" that may be infested, and keep greenhouses as weed free as possible. As soon as an infestation is detected, isolate and treat infested plants.
Early infestations can be easily overlooked due to the mealybug's tendency to hide in protected locations. Mealybugs can be difficult to find if populations are low. Scout regularly to detect early infestations. Look for white flecks or cottony residues along the leaf midribs, on leaf or stem axils and on the underside of leaves. If larger plants are staked, mealybugs hide beneath the tape on the stake that is used to secure the plant. Adult females may crawl off plants and be found on or in brick crevices and under benches where they lay eggs. Honeydew, sooty mold and the presence of ants may also be an indication of a mealybug infestation.
Some of the greenhouse crops prone to mealybug infestations include citrus, coleus, croton, dracaena, hoya, English ivy, ficus, fuchsia, stephanotis, schefflera, hibiscus, mandevilla, strawberry plant (houseplant), jade plants, palms, prayer plants, gardenia, and orchids as well as many other foliage plants. The Mexican mealybug has been found feeding on marigolds, gerbera daisies, poinsettias, begonias and chrysanthemums.
Mealybugs are one of the most difficult greenhouse pests to control. Mealybugs are best treated if detected early, when populations are low. If only a few plants are heavily infested, it may be best to destroy the infested plants to minimize further spread.
A ladybird beetle, commonly known, as the mealybug destroyer (Cryptolamus montrouzieri) is commercially available as a biological control agent. Both adults and larvae feed upon mealybugs. This beetle is most effective when there are high populations of mealybugs because it will fly away if not enough prey is found. Adults are shiny black beetles with a reddish head and thorax and larvae look like a fast moving mealybug. But, unlike mealybugs, the mealybug destroyer larvae will have chewing mouthparts.
A type of entomopathogenic or insect killing fungus, Beauvaria bassiana (Botanigard) is commercially available. This fungus secretes enzymes that dissolve the insect's cuticle. After it enters the insect's body, the fungus produces a toxin that weakens the insect's immune system. When applying this material, thorough spray coverage is needed so that the fungal spores contact the targeted insect and begin the infection process. Repeated applications may be needed.
If only a few plants are heavily infested, growers often destroy the infested plants to minimize further spread.
Control is difficult because of the mealybug’s tendency to hide in protected locations and form dense colonies. The mealybug's waxy covering also helps protect mealybugs from chemical exposure. Use of a spreader sticker may help penetrate mealybug's waxy covering. The young crawlers are not covered by this wax so are the most susceptible life stage. Repeated applications of insecticides are often needed to manage mealybugs. Through coverage is necessary when using contact insecticides. Rotate among insecticides with different modes of action to help delay the development of resistance. Acceptable control is often difficult to achieve.
Consult the most recent edition of New England Greenhouse Floriculture Guide - A Management Guide for Insects, Diseases, Weeds and Growth Regulators for more specific guidelines.
Leanne Pundt, Extension Educator, Commercial Horticulture, University of Connecticut
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Stimmel, J. F. 1979. Citrus Mealybug, Planoccus citri. Regulatory Horticulture. Entomology Circular No. 45. 5(2):21-22. Pennsylvania Department of Agriculture. Bureau of Plant Industry.
Stimmel, J.F. 1975. Longtailed Mealybug, Pseudococcus longispinus [Targ.-Tozz.]
Regulatory Horticulture. Entomology Circular No. 7. 1(2)-13-14.Pennsylvania Department of Agriculture. Bureau of Plant Industry.
Weeden, Shelton, Li and Hoffman (ed). Cryptolamus montrouzieri (Coleptera: Coccinellidae). Mealybug Destroyer. In Biological Control: A Guide to Natural Enemies in North America. http://www.nysaes.cornell.edu/ent/biocontrol/
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