Red scale in rare fruit
Red scale in rare fruit
David Astridge & Harry Fay
Red scale (Aonidiella aurantii) of various sizes (ages).
Description
Adult
Red scale has a thin, circular, leathery covering over the soft, flattened, shield shaped, creamy-yellow insect. The reddish-brown scale cover of the adult female is about 2 mm across. The cover of the male scale is elongated, smaller and paler than that of the female.
Immature stages
The female produces a mobile reddish-yellow crawler stage that can just be seen with the naked eye. The smaller immature female and male scales are similar in shape to the adult female.
Life history
The adult female gives birth to 100-150 mobile young called crawlers, at the rate of two to three per day over a six to eight week period. The crawlers emerge from under their mothers scale cover, and search for a suitable feeding site on leaves, shoots or fruit. Crawlers wandering on the tree canopy can be blown by the wind into neighbouring trees or orchards.
Once a crawler settles, it inserts its mouthparts into the plant and starts feeding on the sap. It secrets a white waxy covering and at this stage is called a 'whitecap'. After a period of feeding and growth the insect moults. The cast skin is attached to the scale cover, giving the cover its typical red colour.
The development stage and sex of red scale can be determined by the shape and size of the scale cover. After the second stage, scales can be identified as male and female. The scale cover of males is elongated, while the scale cover of females is circular.
The male develops through a pre-pupal and pupal stage under a scale cover, before emerging as a delicate, winged insect. It is attracted to the female by a pheromone, and dies without feeding after mating.
There are two to five generations per year below latitude 29oS and five to six above.
Distribution
Red scale is found in all areas where citrus is grown in Australia.
Host range
Red scale also occurs on a wide range of hosts including citrus, passionfruit, roses and carob.
Management
Importance
Minor and sporadic on carob.
Damage
Severe infestations can cause leaf drop and dieback in carob.
Action level
Monitor regularly by sampling five leaves per tree on each of 20 randomly selected trees per one to five hectare block. Once, or twice if necessary, during November-December examine 100 - 200 virgin adult female scale to determine parasitism by Aphytis lingnanensis If parasitism by A.lingnanensis is less than 20%, a parasitoid release of 10 000 per hectare should be made in November to December. Comperiella bifasciata is another important parasitoid. Spray if infestation levels are high and A. lingnanensis parasitism is less than 20% (during December) or 50% (during January).
Control methods
Cultural
Avoid excessive dust from roads or cultivation.
Biological
Parasitoids play a crucial role in the control of the pest and they are described in some detail to assist in recognition. The best way to determine if a parasitoid is present is to lift the scale covering with a pair of tweezers and then examine the body of the pest with a X10 or X15 hand lens, or preferably with a small stereo-microscope. The two most important parasitoids of the scale are Aphytis lingnanensis, a small yellow wasp 1 mm long, and Comperiella bifasciata, a small black wasp 1.5 mm long. Aphytis lingnanensis attacks virgin adult female scales (also second instar and male prepupae). Its eggs, which are white and teardrop-shaped, are laid on or under the scale body as distinct from the scale covering or cap. They hatch into yellow rotund larvae that feed on the scale body, eventually growing almost as big as the body of the scale itself. When fully grown, the parasitic larva forms a yellow pupa about 1 mm long. It is readily recognised because it is surrounded by a number of brown larval faecal pellets. The adult parasitoid also destroys many scales by mutilating them to feed on their body fluids. At 26oC the life cycle takes 16 to 17 days and the adults live for two to three weeks.
Comperiella bifasciata lays its egg entirely within the scale body, parasitising most stages of the scale. At 26oC the life cycle takes three to six weeks depending on the age of the scale at oviposition. The larva is elongate and white and the pupa black. Parasitised scales sometimes have a bloated appearance and the scale covering becomes darkened around the edges. Parasitism levels of 50% to 90% occur where insecticide usage is restricted and providing these levels are present from December on, effective control is obtained.
Chemical
Spray. Good coverage is essential as the scales do not move once they go through the initial crawler stage. The insecticide must therefore hit the scale when applied.
Recommended chemicals
Petroleum oil (narrow range) is approved on carob.
Note: This information was correct at the time of publication. However, it is the user's responsibility to ensure that registered agricultural chemicals are used in accordance with legal requirements. (See Further information). Always read the label.
Further information
- Contact the DPI&F Business Information Centre on 13 25 23 - local call 8 am to 6 pm Monday to Friday (non-Queensland residents phone 07 3404 6999). E-mail: callweb@dpi.qld.gov.au
- Contact the DPI&F bookshop on 07 3239 3772 or DPI&F Shop-online or at some DPI&F offices throughout Queensland for the DPI&F publications
- Infopest CD-ROM contains current national information on registered agricultural chemicals and is available from Infopest, DPI&F, GPO Box 46, Brisbane Qld 4001 or by email from infopest@dpi.qld.gov.au
Recommended reading:
Smith, D. and Papacek, D.F. 1985, Integrated pest management in Queensland citrus , Queensland Agricultural Journal, @b111@b, 249-259.
Broadley, R.H., Smith, D., Owen-Turner, J.C., Chapman, J.C., Banks, A.G. and Mayers, P. 1987, Protect your citrus , Queensland Department Primary Industries, Information Series QI87012.
Papacek, D.F. and Smith, D. 1985, Aphytis lingnanensis In : Singh and Moore (Editors), Handbook of insect rearing, Elsevier, Amsterdam, @b1@b, 488.
Smith, D. 1990, Integrated pest management in Queensland citrus , Australian citrus news @b66(12)@b, 6-12.
Smith, D. 1978, Biological control of scale insects in south-eastern Queensland, 1. Control of red scale Aonidiella aurantii (Maskell) , Journal of Australian Entomological Society @b17@b, 367-371.
Smith, D. Beattie GAC & Broadley, R. (eds.) (1997) 'Citrus pests and their natural enemies' . Queensland Department of Primary Industries, Brisbane.
Swaine, G., Ironside, D.A. and Corcoran, R.J. 1991, Insect pests of fruit and vegetables , 2nd Edition, Queensland Department Primary Industries, Information Series QI91018.
Smith, D. and Papacek, D.L.F. 1984, Integrated control of Aonidiella aurantii (Maskell) and other citrus pests at Mundubbera, Queensland , Queensland Department Primary Industries,
QB 84002.Swaine, G., Ironside, D.A. and Corcoran, R.J. 1991, Insect pests of fruit and vegetables, 2nd Edition, Queensland Department Primary Industries, Information Series QI91018.
Other contacts:
Growcom on 07 3620 3844
Growers interested in the production of minor tropical fruits can join their local branch of the Rare Fruits Council and subscribe to their newsletter. Contact the Rare Fruits Council at PO Box 1375 Aitkenvale 4814
The DPI&F library provides a personalised information search service that may be useful for producers seeking information on minor and exotic crops
DPI&F InfoResearch on 07 3239 6989.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries, Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last updated 19 December 2005
