This tool is part of the Citrus Resource

Citrus Pests

 

Citricola scale

 

Scientific name

 

Coccus pseudomagnoliarum (Hemiptera: Coccidae)

Other common names

 

grey citrus scale

Similar species

 

soft brown scale, Coccus hesperidum

Distribution

 

United States: Arizona, California, Maryland.

Worldwide: Australia, Azerbaijan, Europe, France, Georgia, Greece, Iran, Israel, Italy, Japan, Russia, Sicily, South Korea, Spain, Turkey, and Turkmenistan.

Native to Japan and Southern China.

Diagnostic characteristics

 
Adult females
  • Up to7 mm (0.28 in.) in length.
  • Dark grey.
  • Elongate, oval and slightly convex.
  • Only females are known.
  • Wingless.
Immatures
Eggs
  • Yellow.
  • Oval.
  • Eggs remain under the female prior to hatching.

Hosts

 
Citrus hosts

Most citrus species and their hybrids. Partial host list provided below.

  • grapefruit, Citrus paradisi
  • lemon, Citrus limon
  • Mediterranean mandarin, Citrus deliciosa
  • sour orange, Citrus aurantium
  • sweet orange, Citrus sinensis
  • trifoliate orange, Poncirus trifoliata
  • wu zhu yu, Evodia rutaecarpa
Non-citrus hosts
  • bay laurel, Laurus nobilis
  • Chinese hackberry, Celtis sinensis
  • elm, Ulmus, spp.
  • European hackberry, Celtis australis
  • Japanese elm, Zelkova serrata
  • oleander, Nerium oleander

Host damage

 
Flowers
  • Reduced flowering.
Fruits
  • Reduced fruiting and production.
  • Honeydew excreted by scales coats the outside of fruits and leaves, and promotes the growth of sooty mold fungus that inhibits photosynthesis, weakens the plant, and makes fruit unattractive.
Leaves
  • Pierces and removes nutrients from leaves, and weakens the plant.
Twigs
  • Killed during heavy infestations.

Biology

 

Citricola scales reproduce asexually (parthenogenesis) allowing rapid population growth. Citricola scales have only a single generation per year. This is helpful in identification because all individuals will be approximately the same size on the host plant, while other species will have differing sizes. Adults are found in the spring and early summer on twigs, and immatures are typically found underneath leaves in late summer and fall. Females produce approximately 1000 eggs during their lifetime. Eggs hatch into mobile first instar nymphs, also known as crawlers. Crawlers relocate to find a suitable location, become fixed (sessile), then molt into second instar nymphs that produce large quantities of honeydew and are often tended by ants.

Comments

 

The species name was misspelled when published in 1978. Coccus psuedomagnoliarum is correctly spelled C. pseudomagnoliarum and was also known in the literature as Coccus aegaeus in 1973.

Significant yield reduction of citrus has been noted in California when adult densities exceed one per twig or two first instars on leaves.

All phloem-feeding, honeydew-producing pests have the potential to be tended by ants. The ants feed on the honeydew excreted by the pest and protect the pest from natural enemies. This protection can disrupt biological control programs.

References

 

Eberling, W. 1959. Subtropical fruit pests. Univ. Calif., Div. Agric. Sci., Berkeley, CA.

Flint, M.L. 1999. Pests of the garden and small farm: a grower's guide to using less pesticide. Univ. of California Press: Berkley, CA.

Gill, R.J. 1997. Coccid pests of important crops: Citrus, pp. 207-215. In Y. Ben-Dov, and C.J. Hodgson (eds.). World crop pests, Vol. 7B, Soft scale insects - their biology, natural enemies and control. Elsevier Science B.V.

Grafton-Cardwell, E.E. 2010. Citricola scale. (http://ucanr.org/sites/KACCitrusEntomology/Home/Citricola_scale/).

Miller, G.L., and D.R. Miller. 2003. Invasive soft scales (Hemiptera: Coccidae), and their threat to U.S. agriculture. Proc. Entomol. Soc. Wash. 105: 832-846. (http://www.sel.barc.usda.gov/Coccoidea/MillerMi2003.pdf).

Miller, D.R., A. Rung, G.L. Venable, and R.J. Gill. 2007. Scale insects: Identification tools for species of quarantine significance. CBIT Publishing, Queensland, Australia. (http://www.sel.barc.usda.gov/ScaleKeys/ScaleInsectsHome/ScaleInsectsHome.html).

Velimirovic, V. 1994. Influence of Verticillium lecanii Viegas on Coccus pseudomagnoliarum Kuwana. Zastita bilja (Yugoslavia) 45: 187-193.

Authors

 

Martin, K.W., A.C. Hodges, and N.C. Leppla

 

Citrus Pests
Content last updated June, 2012
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