Scale (Cottony cushion scale) Icerya purchasi
Species: I. purchasi
Binomial name: Icerya purchasi
Common name: Cottony cushion scale, Fluted scale.
Icerya purchasi is a hermaphrodite scale insect that originates from Australia. It feeds on more than 50 families of woody plants most notably on Citrus, Sophora and Pittosporum and occasionally of roses. It is now found worldwide where citrus crops are grown.
Icerya purchasi 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 moult, 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 mould often grows and causes further damage to the host plant. Photosynthesis is disrupted and heavily infested citrus trees may shed all their leaves and fruit, resulting in total yield loss and even death of trees.
Two parasitoids that control I. Purchasi were introduced into New Zealand.
Cyptochetum iceyae (a parasitic fly) in 1888 and 1922 from Australia. It is now well established.
Rodolia cardinalis (Cardinal ladybird) was accidentally introduced to New Zealand, they are no longer very common.
A group of Icerya purchasi on a small branch of a Kōwhai (Sophora microphylla).
The white mass is the egg case attached to the insect.
The underside on this scale insect
Scale on Acacia 'Limelight'
This photo show the hundreds of red eggs in the egg sack that is attached to the insect.
Icerya purchasi secreting honeydew, on which sooty a mould ( an Ascomycete fungi) will grow, blackening the branches.
A photo showing the 6 legs that it holds on with and its sucking mouth parts.
Each scale insect produces 100s of eggs. The photo below is of some of the newly emerged crawlers from four individuals.
A video on the cottony cushion scale.