2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
Acacia pseudoscale lives almost everywhere and develops on various tree and shrub species. Most often it can be found on white acacia, plum, apple and hazel trees. As a result of feeding of females and harmful larvae, the number of leaves and their size noticeably decrease, yellowed leaves quickly fall off, and shoots and twigs gradually dry out. The quality of the crop, as well as its quantity, also decreases markedly. And if the damage is very significant and repeated over several years in a row, then the trees may dry out prematurely. Moreover, honeydew secreted by females in huge quantities serves as a fertile soil for the development of saprophytic fungi that pollute trees
Meet the pest
Convex rounded oval females of acacia false scutes are colored yellow-brown with a pronounced reddish tint. Their keel is usually indistinctly expressed and rather smooth. It is 4 mm high, 2 to 4 mm wide and 4 to 6 mm long. Males, growing in length up to 1, 5 - 1, 6 mm, are endowed with slender thin and elongated bodies. On their little black heads there are three pairs of simple eyes, and the antennae and legs of the pests are painted yellow. The black-brown abdomens and breasts of males are covered with a white coating, and on the tips of their abdomens you can see a pair of threads, the length of which is twice the length of their bodies.
The size of the ellipsoidal eggs of acacia false scutes is about 0.3 mm. The mass of eggs located under the abdomens of the females vaguely resembles heaps of powder. Harmful oval larvae of the first instar, called tramps, reach 0.4 mm in size and have a pale yellow color. Each individual is endowed with a six-segmented antennae and three pairs of legs. And for wintering second instar larvae, black-brown color, well-developed legs and six- or seven-segmented antennae are characteristic.
Second instar larvae overwinter mainly on the undersides of twigs, in ringlets, forks, and trunks. In early spring, before the buds bloom, the larvae begin to actively move to the upper parts of the tree crowns. Usually, such a migration can be observed when the air temperature reaches six to seven degrees. And for the resettlement of the main part of the voracious larvae to be completed, four or five warm and sunny days in a row are enough.
All larvae stick to the undersides of the bark of branches with the help of long proboscis. Sucking the juices, they grow rather quickly, becoming covered with dense networks of numerous wax threads. And after ten to twelve days, they form shields, and the antennae and legs quickly atrophy. Thirty or forty days later, approximately at the end of April or in May, the harmful larvae, having shed, are transformed into females.
The time of the onset of sexual maturity of females coincides with the time of emergence of males and falls around mid-May. It is extremely rare to meet males, since their number in the population fluctuates within 3 - 5%. In this regard, acacia false scutes reproduce mainly by parthenogenetic means. The egg-laying process is completed in six to ten days. The dorsal sides of the females become noticeably denser as they lay eggs, turning into a kind of shields. Their abdomens are gradually retracted, and the resulting spaces are quickly filled with eggs. The total fertility of females in this case reaches from one and a half to two thousand eggs.
Twenty-twenty-five days later, approximately in mid-June, voracious larvae are reborn. Getting out from under the shields, they stick to the lower sides of the leaves (mainly near the veins) and to the fruits. And a week and a half after the revival, the faded tramps pass into the second century. Their feeding ends around the end of September, and the larvae massively migrate to branches with trunks, where they stay for the winter, firmly attached to the tree bark.
Almost throughout the entire territory of Russia, acacia false shields develop in a single generation, and only in the Crimea and in the extreme south does the second optional generation sometimes appear.
How to fight
In the event that for every square meter of shoots there are a couple of hundred larvae of the acacia false shield, the trees begin to be sprayed with ovicides. Such spraying is carried out on dormant buds and only in the early spring period. And trees are treated with insecticides during the mass migration of larvae.
Acacia pseudo-scale insects also have a lot of natural enemies - their larvae are eaten by predatory bugs, sirphid flies, lacewing, spiders, ground beetles and ticks. Not the last role is assigned to endoparasites, mainly representing the chalcid family and some other families - these saviors in some years are able to infect up to 90% of females and up to 50% of larvae. In addition, up to 60% of harmful larvae freeze out in winter, with the onset of spring, tramps are washed away by heavy rains and strong winds blown away, and in dry and hot weather they find their death under the mother's shields.
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