Mealybugs have oval bodies with overlapping soft plates and a cottony white covering. They are related closely to scale insects, but do not attach to a plant and can moved around very slowly. They can stunt a plant or kill it by sucking its juices. They excrete a honeydew which can cause a black, sooty mold.
Mealybug is the common name of insects in Pseudococcidae, a family of unarmored scale insects found in moist, warm climates. They are considered pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees.
Mealybugs are sexually dimorphic, meaning that the sexes have distinct morphological differences. Females are nymphal, exhibit reduced morphology, and are wingless, though unlike many female scale insects, they often retain legs and can move. The females do not change completely and are likely to be neotenic (exhibiting nymphal characteristics). Males are winged and do change completely during their lives. Since mealybugs (as well as all other Hemiptera) are hemimetabolous insects, they do not undergo complete metamorphosis in the true sense of the word, i.e. there are no clear larval, pupal and adult stages, and the wings do not develop internally. However, male mealybugs do exhibit a radical change during their life cycle, changing from wingless, ovoid nymphs to "wasp-like" flying adults.
Mealybug females feed on plant sap, normally in roots or other crevices. They attach themselves to the plant and secrete a powdery wax layer (therefore the name mealybug) used for protection while they suck the plant juices. The males on the other hand, are short-lived as they do not feed at all as adults and only live to fertilize the females. Male citrus mealy bugs fly to the females and resemble fluffy gnats.
Some species of mealybug lay their eggs in the same waxy layer used for protection in quantities of 50–100; other species are born directly from the female.
The most serious pests are mealybugs that feed on citrus; other species damage sugarcane, grapes, pineapple (Jahn et al. 2003), coffee trees, cassava, ferns, cacti, gardenias and orchids. Mealybugs only tend to be serious pests in the presence of ants because the ants protect them from predators and parasites. Mealybugs also infest some species of carnivorous plant such as Sarracenia (pitcher plants), in such cases it is difficult to eradicate them without repeated applications of insecticide such as diazinon. Small infestations may not inflict significant damage. In larger amounts though, they can induce leaf drop.
Note that mealybugs have a symbiotic relationship with ants, which may need to be addressed to clear your mealybug infestation.
Mealybugs are serious houseplant pests around the world, and outdoors they are troublesome pests wherever winters are mild. When you spot an infestation, indoor or out, you can just dip a cotton swab in rubbing alcohol and dab the mealybugs directly with it by hand.
You can hose off plants every 2 weeks with jets of water (or insecticidal soap) in order to blast away as many of the mealybugs and their eggs as possible, as well as the black soot which deters natural predators.
Chemical pesticides known to be effective against mealybugs include malathion, diazinon, acephate, or horticultural oil.
- Maconellicoccus hirsutus - pink hibiscus mealybug, grape mealybug
- Planococcus citri - citrus mealybug
- Pseudococcus viburni - obscure mealybug
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- Sunset National Garden Book. Sunset Books, Inc., 1997. ISBN 0376038608
- Jahn, G. C. and J.W. Beardsley 1994. Big-headed ants, Pheidole megacephala: Interference with the biological control of gray pineapple mealybugs. In D.F. Williams [ed.] "Exotic Ants: Biology, Impact and Control of Introduced Species." Westview Press, Oxford, 199-205.
- Jahn, G. C. and J.W. Beardsley 1998. Presence / absence sampling of mealybugs, ants, and major predators in pineapple. J. Plant Protection in the Tropics 11(1):73-79.
- Jahn, Gary C., J. W. Beardsley and H. González-Hernández 2003. A review of the association of ants with mealybug wilt disease of pineapple. Proceedings of the Hawaiian Entomological Society. 36:9-28.
- BBC gardening advice, mealybugs
- CISR - Vine Mealybug Center for Invasive Species Research summary on Vine Mealybug