Description of adult
The adult female is a yellow, shield-shaped insect covered with a pinkish-greyish-brown, semi-translucent scale 2mm across. The insect is soft-bodied, without appendages and remains in the 1 position feeding through long tubular mouthparts. It produces living young referred to as crawlers. These escape from under the female covering. After about 2 weeks the male scale becomes mussel-shaped and can be distinguished from the circular female scale. The adult male emerges as fragile, winged insect.
Crawlers cannot be seen with the naked eye. They are yellow-cream, have legs, and disperse over the tree to a position where they settle permanently and begin to feed. Once the crawlers settle they quickly form immature scales similar to adult females except smaller.
Both males and females are ready for mating about 3 weeks after the crawlers settle. The male dies soon after mating. The fertilised female begins to produce crawlers 2 weeks later then dies after a further 3-4 weeks. These times are greatly extended in winter so that about 5 generations are produced in a year.
Northern Australia as far south as Gladstone (24oS) on the east coast.
Plants from the following families: Anacardiaceae, Apocynaceae, Caricaceae, Combretaceae, Euphorbiaceae, Musaceae, Palmae, Rosaceae, Salicaceae, and Vitidaceae.
Hosts of horticultural interest include banana, coconut, castor oil, frangipani, grape, mango, oleander, papaya, rose and willow.
Although other hosts have been recorded in Queensland, heavy infestations have only been recorded on castor oil and papaya.
Minor and infrequent since the release of a wasp (Comperiella lemniscata Compere and Annecke) for biological control. Population increases are common in late summer and autumn. Oriental scale is not a pest south of Yarwun.
Scales suck the sap. Heavy scale infestations on papaya trunks cause tissue damage allowing fungal infection. Infested trees become very unthrifty and may snap off in wind or die. Both the skin and fruit of infested fruit fail to ripen in the area surrounding the individual scales so that the ripe fruit has green spots and is inedible. Fruit infested while still expanding develop a sunken area around the scale.
Examine the trunks and 5 fruit on 20 widely separated trees throughout each 0.5ha of crop. Order and release Chilocorus circumdatus if 1 or more trees have a large flush of (medium sized) scale. A release is unnecessary if high levels of parasitism (70% Encarsia citrina (Craw) in medium (2nd instar) sized scales, and 70% Comperiella lemniscata in fully-grown female (3rd instar) scales) are already occurring.
Assessment of parasitism levels requires training and equipment such as a microscope or high magnification hand lens. Examine 20 large and 20 medium scales for parasitoids on each of 10 fruit. Pick the fruit with the most scale or collect more than 10 fruit if scale populations are too low to give 20 of each sized scale with only 10 fruit.
Cut out the occasional seriously infested trees. Usually the scale does not spread to many nearby trees and it may be preferable to leave the infested trees to allow parasitoids to breed up on the scale.
The parasitoids, Encarsia citrina, and Comperiella lemniscata are very important in the control of this pest. The 1 caterpillar and 4 ladybeetle predators, Batrachedra arenosella and Telsimia sp., Lindores lophanthae, Chilocorus circumdatus and C. baileyi respectively, are usually only present and effective when scale populations are very dense. Because of the importance of these parasitoids and predators, every effort should be made to avoid the use of pesticides over the whole plantation.
As soon as a large increase in medium sized scales is noticed, order C. circumdatus predators. Apply at the rate of 750 per hectare (300 per acre). If part of the papaya crop is infested, only make releases in that area. Another occasional parasitoid, Aphytis melinus was used as a biological pesticide but it often did not persist for longer than 12 weeks and it did not survive the winter. The 2 important parasitoids above are established throughout Queensland although it may occasionally be necessary to introduce them in newer, more remote papaya growing areas.
Their populations decline with scale populations during winter. Most parasitoids prefer healthy well-foliaged trees to provide them with shelter from extremes of heat and low humidity. Prolonged periods of temperature extremes, and dust are harmful to many beneficial insects. Growing healthy plants, using cover crops or mulches between rows and avoiding the use of dusty tracks will enhance parasitoid activity.
Apply recommended chemical if C. circumdatus predators are not available or if the scale problem rapidly increases. To avoid plant/fruit damage apply in cooler weather and ensure continual agitation in the tank. One or 2 oil applications should enable the parasitoids to regain control of the scale without greatly reducing the parasitoid numbers. If the problem is restricted to a few trees only, spray these.
Check the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat this pest on the target crop in your location. Always read the label and observe withholding periods.
- Last reviewed: 19 Oct 2022
- Last updated: 19 Oct 2022