Pink wax scale
Description of adult
A hard pink to pale red wax covering protects the adult female of pink wax scale. The scale is about 3–4mm long, and globular and smooth in shape, with 2 lobes on each side and a depression at the top.
Eggs are brick red, and after laying them the female holds them in a cavity under her body. The eggs hatch into crawlers, which are small and mobile, with 3 pairs of legs, 2 eye-spots and paired antennae. The crawlers settle down and moult, inserting their proboscis to start sucking sap. At the same time they commence secreting the waxy covering that gives the scale its name. The wax is white at first, later turning pink.
The scale has 2 generations per year in Queensland. Depending on prevailing temperatures, crawlers of the first generation emerge from mid-September until early December, but mostly from mid-October to mid-November. Crawlers of the second generation emerge in February to late April.
The insect occurs along the east coast of Australia as far south as Sydney.
Citrus, mango, avocado, custard apple, longan, many native shrubs (umbrella tree, lilly pilly, pittosporum and callistemon) and exotic ornamentals (e.g. ixora).
Minor and frequent.
Adults and nymphs suck the sap of shoots, leaves and fruit stalks. Protein is the main component extracted from the sap, while the excess containing sugars is excreted. This sugary excretion from the scales, which covers the leaves, provides a medium for the growth of black sooty mould. The sooty mould reduces the amount of light available for photosynthesis in the leaves and spoils the appearance of fruit. Sooty mould is epiphytic and not parasitic.
Examine 5 leaves/stems on 20 trees widely spaced throughout the crop. Spray if more than 5 out of 100 of these plant parts are heavily infested with the scale. Check the whole orchard for trees with sooty mould on leaves, stems and fruit to obtain an indication of the level of infestation, especially when conditions are humid. If significant infestation is noted in spring, spray to reduce the population before crawlers hatch.
Parasites may be rendered ineffective because of sprays applied to control macadamia nutborer. A parasite, Anicetus beneficus was introduced for control of pink wax scale in 1977. It is very effective where no disruptive pesticides are used, but it is also slow to disperse. Introduction of parasitized scale into the orchard on other infested host plants such as the umbrella tree is usually necessary. If the parasite is present, some scales will have a circular hole where the parasite has emerged.
Other common parasites include the wasps Metapyhcus varius, Scutellista caerulea and Coccophagus ceroplastae.
Predators include the ladybeetles, Rhyzobius ventralis, Cryptolaemus montrouzieri and Harmonia conformis, the caterpillar Catoblemma dubia and lacewings, Mallada spp.
The fungus, Verticillium lecanii may infect high density populations of pink wax scale under humid conditions.
Spray infested trees with the recommended chemicals. Because scales are sedentary, complete coverage of foliage is required to achieve good control. A spray droplet must contact each scale to kill it. Apply sprays only when all eggs under adult scales have hatched. Egg hatch is complete when young scales are noticed on leaves, and no liquid exudes when old scales are squashed. At this point, highly susceptible young scales line the midribs of the outer foliage.
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: 22 May 2023