Mealybug

Mealybugs are insects in the family Pseudococcidae, unarmored scale insects found in moist, warm habitats. Of the more than 2000 described species, many are considered pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees and also act as a vector for several plant diseases. Some ants live in symbiotic relationships with them, protecting them from predators and feeding off the honeydew which they excrete.

Description

Mealybugs are sexually dimorphic: females appear as nymphs, exhibiting reduced morphology, and lack wings, although unlike many female scale insects, they often retain legs and can move. Males are smaller, gnat-like and have wings. Since mealybugs (as well as all other Hemiptera) are hemimetabolous insects, they do not undergo complete metamorphosis in the true sense of the word. 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, and in a few cases the bottoms of stored fruit. They attach themselves to the plant and secrete a powdery wax layer (hence the name "mealy" bug) used for protection while they suck the plant juices. In Asia, mango mealybug is considered a major menace for the mango crop. 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, papaya, mulberry, sunflower and orchids. Mealybugs only tend to be serious pests in the presence of ants because the ants protect them from predators and parasites. Mealybugs are also a vector of viruses in grapevines, spreading grapevine leafroll and grapevine red blotch viruses. 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. In recent years, some of the mealybug species have become invasive pests in localities posing a great problem to the new agro-ecosystems. In India, Withania somnifera plant have been reported as a new reservoir host for an invasive mealybug species Phenacoccus solenopsis.

Some mealybugs of the Hypogeococcus are used as biological pest controls of invasive cacti in South Africa, including Harrisia balansae, H. martinii, and Opuntia cespitosa.

Fossil specimens of genus Acropyga ants have been recovered from the Burdigalian stage Dominican amber deposits and several individuals are preserved carrying the extinct mealybug genus Electromyrmococcus. These fossils represent the oldest record of the symbiosis between mealybugs and Acropyga species ants.

Control methods

Insecticides such as pyrethroids (e.g. permethrin, bifenthrin, cyfluthrin) have been used for control, but this approach is often considered counter-productive due to mortality of mealybug natural enemies.

Some gardeners use species of predatory beetles (e.g. Cryptolaemus) and green lacewings (Chrysopidae) larvae to control mealybug infestations, as the larval lacewings are voracious predators of aphids and other small insects.

Metabolism

Mealybugs have a highly sophisticated metabolism that involves not one but two bacterial endosymbionts, one inside the other. The endosymbionts make essential amino acids that the mealybug is not able to acquire directly from its diet. Genetically, mealybugs rely on a "mosaic" of metabolic pathways in which proteins are transported across membranes between what were once independent organisms.

Use in the Textile Industry

In Oaxaca Mexico, where mealy bugs are known as cochinilla algodonosa, the insects are intentionally cultivated and farmed. Dried mealy bugs are traditionally ground into a red dust, which is used to dye fabrics.

Genera

Extinct genera:

• †Electromyrmococcus Williams, 2001
• †Phyllococcus Ehrhorn, 1916 (monotypic)

Note:

• the genus Puto is now placed in its own family
• Lachnodius Maskell, 1896 is now placed in the Eriococcidae

References

Further reading

• 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. Boulder, Col.: Westview Press, 199–205. ISBN 9780813386157.
• 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.

External links

• NCIPM (National Centre for Integrated Pest Management) – Cotton Mealybugs
• Mealy bugs Pseudococcus spp.—BBC gardening advice
• CISR – Vine Mealybug—Center for Invasive Species Research summary on Vine Mealybug
• On the University of Florida / Institute of Food and Agricultural Sciences Featured Creatures website:
  • Hypogeococcus pungens
  • Nipaecoccus nipae, coconut mealybug

1. Cryptolaemus montrouzieri
2. Mango mealybug
3. Planococcus citri
4. Pseudococcus viburni
5. Blue-green mealybugs
6. Balanococcus cordylinidis
7. Maconellicoccus hirsutus
8. Pseudococcus longispinus
9. Phenacoccus solenopsis
10. Pseudococcus comstocki
11. Scale insect
12. Planococcus ficus
13. Phenacoccus manihoti
14. Withania somnifera
15. Nephus (Scymnobius) sordidus
16. Nipponaclerda biwakoensis
17. Phenacoccus
18. Pseudococcus maritimus
19. Ferrisia virgata
20. Ensete ventricosum