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 convexconvex:
  shaped or curved like the outward surface of a sphere
  .
• Only females are known.
• Wingless.

Immatures

• Two nymphal instars prior to maturation.
• First instars are translucent yellow-green to brown, mobilemobile:
  able to move
  crawlers.
• Second instarinstar:
  immature stages (larva or nymph) of insects in between molts
  is mottled dark brown.
• Elongate, oval, and slightly convexconvex:
  shaped or curved like the outward surface of a sphere
  .

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 honeydew:
  the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
  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 generationgeneration:
the time it takes for an insect to develop from egg to adult
per year. This is helpful in identification because all individuals will be approximately the same size on the host planthost plant:
the plant the provides sustenance for an insect
, while other species will have differing sizes. Adults are found in the spring and early summer on twigs, and immaturesimmatures:
term used to describe the sub-adult stages of insects that do not undergo complete metamorphosis; see also nymph
are typically found underneath leaves in late summer and fall. Females produce approximately 1000 eggs during their lifetime. Eggs hatch into mobilemobile:
able to move
first instarinstar:
immature stages (larva or nymph) of insects in between molts
nymphs, also known as crawlers. Crawlers relocate to find a suitable location, become fixed (sessile), then moltmolt:
process of shedding the external skeleton during periods of growth; occurs between successive instars of a larva or nymph
into second instarinstar:
immature stages (larva or nymph) of insects in between molts
nymphs that produce large quantities of honeydewhoneydew:
the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
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 honeydewhoneydew:
the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
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. Invasiveinvasive:
term used to describe species that are not native and have the ability to adversely effect habitats they invade either ecologically or economically
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