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California Red Scale

Red Scale on twig.
Red scale on fruit.
Aonidiella damage on Leaf.
Aonidiella damage on fruit.

Scientific Name

Aonidiella aurantii



The adult female has a round, slightly convex, leathery covering, 1-2 mm (0.039 - 0.079 inch) in diameter, with a central tip. It is semi-transparent, with a reddish-brown color. The insect itself, which is normally hidden, is light orange-yellow.
Males develop under an oval cover, about 1-1.3 mm (0.039 - 0.05 inch) in length, which is smaller and paler than that of the females. When mature, the males are 0.8-1.2 mm (0.03 - 0.046 inch) in length, yellowish, and have a delicate pair of wings.


Aonidiella aurantii settles on all aerial parts of the tree: on leaves, fruits, twigs and branches. It feeds by ingesting the contents of parenchyma cells. The toxic effect of the insect's saliva, which interferes with cell metabolism, is at least as important as the loss of water and nutrients with the cell sap. Attack by this insect will initially lead to yellowing of leaves. With growing severity of infestation, the leaves wilt and plants gradually become defoliated. Fruits may fall off in large numbers, sometimes after having become literally encrusted with scales. Twigs and small branches may die back, and in extreme cases, or with young trees, the whole plant can be killed. Damage is particularly severe during hot weather due to the water stress it entails. Long-lasting, heavy infestations may reduce yield not only in the current season, but also in several following years as well.

Fruits that have been attacked during their early development show noticeable pits. Even when dead, the scales remain firmly attached to the surface and are hard to remove. Thus the remaining yield has a considerably-reduced market value.


Red scales are ovoviviparous: they produce live offspring even though the egg stage is not completely eliminated (the nymphs hatch inside the female's body). Each female can produce 100-150 young over a 6-8 week period, at a rate of 1-3 per day. These „crawlers“ are mobile and very small, and are therefore easily transported by wind, by birds, but also by humans and their tools. For several hours after birth they disperse over the tree in search of a feeding site. They are positively phototactic (attracted by light), which tends to lead them towards young twigs, leaves and fruits, where they prefer to settle in small depressions. Once they have inserted their mouthparts and started feeding, they produce a white woolly wax covering („whitecap“ stage). With their first moult, they assume the typical scale appearance. After a few days, the sexes can be distinguished by their form and further development. The female moults into the grey stage, named after the grey color of the scale's rim. Mating occurs at the beginning of this stage, before the female finally matures.

The male passes through the pre-pupal and pupal stages under its cover before emerging as a winged adult: it then locates the female by its pheromones and mates. It does not take up food, and only lives at most one day. There are usually more females than males in the population (with a ratio of up to 2.6:1). The life-cycle of the female lasts from 55-138 days, but that of the male only 26-76 days. Aonidiella aurantii has 2-7 largely overlapping generations per year. Active crawlers are mainly found between April and November, but all stages are able to overwinter. The peak of infestation mostly occurs during the hot and dry summer months.

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