Scale Insects

Various

Family: Coccidae (Soft scales) and Diaspididae (Armoured scales)

Order: Hemiptera

Description:

Adult

Colour - Dull with a wax scale covering.

Body - Up to 10 mm. Oval. Soft. Under a domed covering.

Wings - 1 Pair in males, none in females. Wing-span 1 mm

Mouthparts - Stylet. Sucking. Near rear of head.

Antennae - Very small or absent. 3-10 segments.

Eyes - 2. Compound.

Legs -Very small or absent. Feet (Tarsi) have 4 segments.

Head - fused to thorax.

Thorax - 3 segments.

Abdomen - Eight pairs of spiracles on underside. Segments ill defined

Egg - ovoid.

Habits - Males fly but don't feed. First instar mobile. Female sedentary and protects eggs. Some species may not produce males and females can produce eggs directly.

Nymphs

Usually 3-5 stages (instars). Look quite different to the adults.

Biology:

There are two main types the soft scales that are usually from the Coccidae family and the armoured scales that are from the Diaspididae family.

Life Cycle:

Eggs are laid under or stay within the female's body then hatch to produce nymphs or crawlers. Some species give birth to live young. First instar nymph is highly mobile. Later instars less so. The mature female is sedentary, headless, legless and wingless and attaches herself to the plant by her mouthparts (stylet) and forms a waxy, leathery or cottony covering over her soft body. They can produce more tan 150 eggs then die. In some species fertilisation is not required and males have not been found. The males of other species live under their protective covering until mature then emerged as winged adults. They tend to live in colonies. They may be tended by ants that feed on the honey dew and protect them from predation.

Habitats:

Origin and History:

Distribution:

Significance:

Sooty moulds growing on the honey dew excreted by scales may make fruit unsaleable. This is usually the greatest cause of economic loss. Ceroplastes destructor is a pest of citrus. Ceroplastes rubens, Coccus hesperidum, Parasaissetia nigra and Saissetia coffeae are pest of many fruit species. Pulvinaria elongata and Symonicoccus attack sugar cane and other grasses. Other species damage cut flowers and vegetables. Some have toxic saliva which may kill plant tissue and cause distortions.

They are common pest of indoor plants.

Severe infestations may cause defoliation and occasionally death of plants.

Cochineal and shellac are made from scale insects.

Management and Control:

White oil, paraffin oil, petroleum oil, soap solutions and insecticides are used on heavy infestations. Control ants as these will often protect scales from predators.

Introduce parasitic wasps such as Aphytis melinus, Aphytis lignanensis and Comperiella species.

Scale eating ladybirds (Rhyzobius lophanthae) are also used to help control scale insects.

Soft scale insects are usually harder to control than the armoured scale insects.

Large trees may be stem injected.

For stem injection, mix 10 mL dimethoate400 with 10 mL water. Drill 12 mm diameter holes angled downwards at 45 degrees about 25 mm deep into the sapwood at 100 mm spacings around the trunk and about 250 mm above ground level. Inject 3 mL of the dimethoate mix into each hole. Plug the holes with putty a few hours later to prevent decay

Thresholds:

Depends on species. If predators and parasites have not been recently killed then very often no treatment is required.

Related Species:

There are hundreds of scale insect species in Australia.

Similar Species:

Aphids, Lerps, various 'bugs' and leafhoppers are sometimes confused with scales.

Striped mealy bug (Ferrisia virgata) is an exotic pest. Please report if found.

Citrophilus mealy bug (Pseudococcus calceolariae) is an exotic pest. Please report if found.

References:

CSIRO. The Insects of Australia. Melbourne University Press. (1991) p60, 182, 443, 458, 461-464, 769, 967, 968, 987.

Goode, J. Insects of Australia. Angus and Robertson. p61.

Hoffman & Botha (2006) Garden Note #206, DAFWA.

Jones, D. & Elliot, R. Pests Diseases and Ailments of Plants. Lothian Publishing Australian Co. p71-73.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.