Icerya purchasi
Encyclopedia
Icerya purchasi is a scale insect
that feeds on several species of woody plants, most notably on Citrus
and Pittosporum
. Originally identified in 1878 as a New Zealand
located pest of kangaroo acacia
, it is now found worldwide where citrus crops are grown.
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.
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.
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.
Icerya purchasi is important as one of the first major successes of biological control. Importations of the vedalia ladybeetle (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 Cryptochaetum 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 not recommended, although it affects other scale insects, because it has no effect on this species but is very toxic to the vedalia ladybug.
Scale insect
The scale insects are small insects of the order Hemiptera, generally classified as the superfamily Coccoidea. There are about 8,000 species of scale insects.-Ecology:...
that feeds on several species of woody plants, most notably on Citrus
Citrus
Citrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...
and Pittosporum
Pittosporum
Pittosporum is a genus of about 200 species of flowering plants in the family Pittosporaceae. The genus is probably Gondwanan in origin; its present range extends from Australasia, Oceania, eastern Asia and some parts of Africa. Citriobatus is usually included here, but might be a distinct genus...
. Originally identified in 1878 as a New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
located pest of kangaroo acacia
Acacia paradoxa
Acacia paradoxa is a plant in the Fabaceae family. Its common names include kangaroo thorn, prickly wattle, hedge wattle and paradox acacia. This is a large shrub up to 3 metres tall and wide. It is dense with foliage; the leaves are actually enlarged petioles known as phyllodes. They are crinkly...
, it is now found worldwide where citrus crops are grown.
Life cycle
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
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.
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.
In addition to the direct damage from sap sucking, the insects also secrete honeydew
Honeydew (secretion)
Honeydew is a sugar-rich sticky liquid, secreted by aphids and some scale insects as they feed on plant sap. When their mouthpart penetrates the phloem, the sugary, high-pressure liquid is forced out of the gut's terminal opening. Honeydew is particularly common as a secretion in the Hemipteran...
, on which sooty mold
Sooty mold
Sooty molds are Ascomycete fungi which grow on plant exudates and the sugary honeydew secreted by insects such as aphids, scales, the whitefly, and other insects which suck sap from their host plants. The name itself is descriptive, as sooty mold is a black, powdery coating adhering to the leaves...
often grows and causes further damage to the host plant. Some ants will also consume this honeydew.
Biological control
Rodolia cardinalis
Rodolia cardinalis is a species of ladybird beetle that is sometimes described as endemic to Australia.-New Zealand:...
) in 1888-1889 by C. V. Riley
Charles Valentine Riley
Charles Valentine Riley was a British-born American entomologist and artist.-Early Life:The son of a Church of England minister, Charles Valentine Riley was born on 19 September, 1843 in London’s Chelsea district. When he was around eleven his parents, the Rev. Charles and Mary Riley, chose to...
, 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 Cryptochaetum iceryae has also been introduced to California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
as an additional control vector. Use of insecticides as a control is recommended only if no biological control species is present. Imidacloprid
Imidacloprid
Imidacloprid is a nicotine-based, systemic insecticide, which acts as a neurotoxin and belongs to a class of chemicals called the neonicotinoids. Although it is now off patent, the primary manufacturer of this chemical is Bayer CropScience,...
is especially not recommended, although it affects other scale insects, because it has no effect on this species but is very toxic to the vedalia ladybug.