Icerya purchasi

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Icerya purchasi
Icerya purchasi , female
Scientific classification
I. purchasi
Binomial name
Icerya purchasi
Maskell, 1878
  • Icerya purchasi crawii Cockerell, 1897
  • Icerya purchasi maskelli Cockerell, 1897
  • Icerya purchasi citriperda Hempel, 1920

Icerya purchasi (common name: cottony cushion scale) is a scale insect that feeds on more than 65 families of woody plants,[1] most notably on Citrus and Pittosporum. Originally described in 1878 from specimens collected in New Zealand as pests of kangaroo acacia,[2] it is now found worldwide where citrus crops are grown. The cottony cushion scale originates from Australia.[3]

Life cycle[edit]

Small colony

This scale infests twigs and branches. The mature hermaphrodite is oval in shape, reddish-brown with black hairs, 5 mm long. When mature, the insect remains stationary, attaches itself to the plant by waxy secretions, and produces a white egg sac in grooves, by extrusion, in the body which encases hundreds of red eggs. The egg sac will grow to be two to three times as long as the body. Newly hatched nymphs are the primary dispersal stage, with dispersion known to occur by wind and by crawling. Early stage nymphs feed from the midrib veins of leaves and small twigs, and do the bulk of the damage. At each molt, they leave at the old feeding point the former skin and the waxy secretions in which they had covered themselves and from which their common name is derived. Unlike many other scale insects, they retain legs and a limited mobility in all life stages. Older nymphs migrate to larger twigs and eventually as adults to branches and the trunk. Their life cycle is highly temperature dependent, as the length of time in each stage of life is longer in cold temperatures than high temperatures.

In addition to the direct damage from sap sucking, the insects also secrete honeydew, on which sooty mold often grows and causes further damage to the host plant. Some ants will also consume this honeydew.


'It turns out that females in these hermaphrodite insects are not really fertilizing their eggs themselves, but instead are having this done by a parasitic tissue that infects them at birth,' says Laura Ross of Oxford University's Department of Zoology. ‘It seems that this infectious tissue derives from left-over sperm from their father, who has found a sneaky way of having more children by mating with his daughters.'[4]

True males are uncommon to rare overall, and in many infestations are not present. Pure females are unknown. Self-fertilization by a hermaphrodite will produce only hermaphrodites. Matings of a male and hermaphrodite will produce both males and hermaphrodites.[5]

Biological control[edit]

Rodolia cardinalis feeding on cottony cushion scale

Icerya purchasi is important as one of the first major successes of biological control. Importations of the vedalia ladybird (Rodolia cardinalis) in 1888-1889 by C. V. Riley, later head of the USDA's Division of Entomology, resulted in swift reductions of I. purchasi populations, saving the burgeoning Californian citrus industry from this destructive pest.

A second biological control, the parasitic fly Cryptochetum iceryae has also been introduced to California as an additional control vector. Use of insecticides as a control is recommended only if no biological control species is present. Imidacloprid is especially contraindicated, since it has no effect on this species, but is very toxic to Rodolia cardinalis.


  1. ^ ScaleNet
  2. ^ Maskell, W.M. 1879 (1878). On some Coccidae in New Zealand. Transactions and Proceedings of the New Zealand Institute 11: 187-228.
  3. ^ Nair, K. S. S. (2007). Tropical Forest Insect Pests: Ecology, Impact, and Management. Cambridge University Press. ISBN 9781139464857.
  4. ^
  5. ^ Gardner, Andy; Ross, Laura (2011). "The Evolution of Hermaphroditism by an Infectious Male-Derived Cell Lineage: An Inclusive-Fitness Analysis". The American Naturalist. 178 (2): 191–201. doi:10.1086/660823. PMID 21750383. Lay summaryNational Geographic News (August 17, 2011).

External links[edit]