California red scale

Scientific name

Aonidiella aurantii (Hemiptera: Diaspididae)

Other common names

red scale, red orange scale, orange scale

Similar species

Aspidiotus macfarlanei

inornate scale, Aonidiella inornata

yellow scale, Aonidiella citrina
Female California red scales settle on wood, fruit, and leaves, as opposed to yellow scales, which are usually found on leaves and fruit.

Distribution

United States: Alabama, Arizona, California, Florida, Georgia, Kansas, Missouri, New Jersey, Pennsylvania, Oregon, and Texas.

Worldwide: Widespread where host plants are grown including Africa, Asia, Australia, Central America, Europe, and South America. Native to Southeast Asia.

Diagnostic characteristics

Adult females

• 1.5 - 2.0 mm (0.06 - 0.08 in.) in length.
• Semi-translucent, reddish-brown or reddish-grey cover.
• Cover is a non-living protective shield produced from glue-like excretions and previously-shed skins.
• Cover is flat and kidney-shaped.
• Females are wingless.
• Antennae reduced to single-segmented stubs.
• Females always lack legs and are immobile.
• Adult female life stage should be used for identification.

Adult males

• 1.0 - 1.3 mm (0.04 - 0.05 in.) in length.
• Golden with a distinctive brown band across the thoraxthorax:
  one of the three main body segments in an insect, located between the head and abdomen, where the wings and legs of the insect attach
  .
• Elongate, resembles a gnat.
• A translucent pair of wings is folded back over the body.

Immature females

• Mobile mobile:
  able to move
  only in their first crawlercrawler:
  the mobile first instar of many scale species
  stage until they find a suitable site to feed, then they become immobile (sessile).
• Transition through two additional instars to become adults.
• Crawlers are white and become grayish to red as they moltmolt:
  process of shedding the external skeleton during periods of growth; occurs between successive instars of a larva or nymph
  .
• Crawlers are oval, later instars are round and resemble adults, just smaller.

Immature males

• Two nymphal instars, followed by a pre-pupal and pupal stage.
• Crawlers are white and become grayish to red as they moltmolt:
  process of shedding the external skeleton during periods of growth; occurs between successive instars of a larva or nymph
  .
• Red-brown skins shed from previous developmental stages near the rear of the insect (subterminal exuviae).

Eggs

• No eggs are laid; females bear live young called crawlers.

Hosts

Citrus hosts

Citrus susceptibility to scales varies by species.

• Cleopatra or dwarf tangerine, Citrus reshni
• common mandarins (including tangerine), Citrus reticulata
• grapefruit, Citrus paradisi
• king mandarin, Citrus nobilis
• lemon, Citrus limon
• Mediterranean mandarin, Citrus deliciosa
• pummelo, Citrus maxima
• Satsuma mandarin, Citrus unshiu
• sour orange, Citrus aurantium
• sweet orange, Citrus sinensis

Non-citrus hosts

Broad host rangehost range:
the range of species that a particular organism can feed on to achieve successful growth and reproduction
. A partial list includes:

• Acacia spp.
• grape, Vitis spp.
• guava, Psidium guajava
• Magnolia spp.
• mango, Mangifera indica
• mulberry, Morus spp.
• olive, Olea europaea
• palm, many genera
• papaya, Carica papaya
• privet, Ligustrum spp.
• Rosa spp.

Host damage

Flowers

• Attacked less often than leaves and twigs.

Fruits

• Infested less often than leaves, but fruit pitting or fruit drop can occur.
• 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

• Preferred by the scale and cause yellowing of leaves and leaf drop.
• Upper surface of leaves typically near the mid-rib or large veins.
• Toxin injected by the scales causes a yellow spot around its feeding area.

Roots

• Occasionally infested by scales.

Trunk

• Can become heavily infested by scales, especially young citrus trees.

Twigs

• Can have noticeable twig and limb dieback due to the injected toxin when scale densities are high.

Biology

California red scales overwinter on twigs and leaves after harvest. Adult females are legless and immobile. Individual females can produce 150 crawlers. Crawlers, the mobilemobile:
able to move
first stage of the scale, emerge from under the female scale and seek a feeding site generally within one meter of its origin on a leaf, twig, or fruit. Female crawlers progress through three nymphal instars to become reproductive adults. Males progress through two nymphal instars, a pre-pupapre-pupa:
the non-feeding last instar larva of insects that undergo complete metamorphosis
, and pupa phase to become winged adults. Adult males are short-lived and expire soon after mating. The life cycle can be completed in six weeks, and thus, multiple generations can occur annually.

The presence of some species of ants can allow dramatic increases in scale populations due to the protection from predators and parasitoids the scales receive from ants. Populations can increase very rapidly and cause extensive damage to citrus.

Comments

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

Flint, M.L. 1991. Scale insects in integrated pest management for citrus, pp. 57-65. Pub. 3303. University of California, Division of Agriculture and Natural Resources: ANR Publications.

Forster, L.D., R.F. Luck, and E.E. Grafton-Cardwell. 1995. Life stages of California red scale and its parasitoids, Pub. 21529. University of California, Division of Agriculture and Natural Resources.(http://groups.ucanr.org/citrusentomology/files/75934.pdf).

Luck, R.L., and M. Hoddle. 2009. California red scale, Aonidiella aurantii. (http://cisr.ucr.edu/california_red_scale.html).

Miller, D.R., and J.A. Davidson. 2005. Armored scale insect pests of trees and shrubs (Hemiptera: Diaspididae). Cornell University Press: Ithaca, N.Y.

Statewide IPM Program, Agriculture and Natural Resources, University of California. 2011. University of California, pest management guidelines - citrus: California red scale and yellow scale. UC-ANR Publication 3441 (http://www.ipm.ucdavis.edu/PMG/r107301111.html).

Watson, G.W., and S.A. Ulenberg (eds.). 2005. Arthropods of economic importance - Diaspididae of the world in World Biodiversity database. (http://nlbif.eti.uva.nl/bis/diaspididae.phpselected=beschrijving&menuentry=soorten&id=83).

Authors

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