Apple aphid
Apple aphid | ||||||||||||
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![]() Apple aphid ( Eriosoma lanigerum ) |
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Systematics | ||||||||||||
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Scientific name | ||||||||||||
Eriosoma lanigerum | ||||||||||||
( Hausmann , 1802) |
The apple aphid ( Eriosoma lanigerum ) is a plant louse from the family of the tube aphids (Aphididae). It originally comes from North America , but was introduced by humans to different parts of the world, such as Europe and New Zealand.
features
The far more common, wingless adults are about 1.8 millimeters long and are dark brown to dark purple in color. Your siphons ( siphunculi ) are very short and almost invisible. The bodies of the animals that live above the earth are covered with long, white, wool-like wax threads. The animals living underground are covered with whitish-blue wax particles. The winged adults are slightly larger than the wingless, matt blue-gray to black in color and only slightly covered with wax excretions. The forewings are transparent, their veins have characteristic strong, dark veins on the front.
The nymphs have an elongated and slightly flattened body, are pale gray to reddish brown in color, and gradually produce bluish-white wax secretions as they develop. The animals are initially about 0.6 millimeters long and reach 1.3 millimeters in the last stage. Their very distinctive proboscis is at least as long as their body.
The oval eggs are 0.3 millimeters long, brown to purple in color and are also coated with wax.
Way of life
In North America, where sexual reproduction can also be observed, the animals are mainly found on the American elm ( Ulmus americana ). In Europe the species reproduces almost exclusively parthenogenetically and lives on apples ( Malus ). The species can also be found on quince ( Cydonia oblonga ) and rarely also on pears ( Pyrus ). Imagines such as nymphs suck sap from young, one to three year old shoots, but also from injuries to old branches and the trunk. They don't suck on leaves.
The species usually overwinters as a nymph on the roots of the host plants, one to two meters below the ground. Nymphs and adults can survive in mild winters but also above ground in well-protected places. When the population density is high, the animals sometimes hibernate as eggs in cracks in the bark. From March to April, the wingless females begin to give birth to live nymphs. A total of around 100 to 120 offspring are produced by autumn, with winged females only appearing when colonies are overpopulated, usually from July. There are 10 to 12 generations per year. In the first stage the nymphs are very active and can migrate from the roots to the above-ground parts of the plants and vice versa. But they can also be transported to other host plants by external influences such as wind or by other animals. The animals go through four nymph stages before they molt to the imago. In autumn, some of the nymphs develop into wingless males that mate with wingless females. These then each lay a single, relatively large egg. It is not yet sufficiently clear when sexual reproduction takes place; However, it seems to take place only in exceptional cases on apple trees, as a rule it occurs on American elm.
Economic importance and control
Sucking the animals causes plant galls and woody outgrowths. Heavy infestation on the roots can cause them to die, which subsequently affects the growth of the plants. Young trees can sometimes die, but older trees are hardly affected. When the galls break open, fungal infections and other plant diseases can increase. The fruits on apple trees can also be affected by colonization of the stem and by excretions of wax and honeydew , which reduces the sales value.
Control is usually only required in the event of severe infestation and the feared damage. There are insecticides against apple aphids based on dimethoate , endosulfan , chlorpyrifos or methyl parathion , among others . Only the infestation on the above-ground parts of the plant can be treated, the control of the animals on the roots is not possible.
Natural enemies
The larvae of the woolly aphid-Zehrwespe ( Aphelinus mali ), a jewel wasps -Art, develop as parasites in blood apple lice. However, they are very sensitive to insecticides and therefore do not occur in agricultural plantations. There are also a number of different predatory predators from lice such as ladybirds , lacewing and hoverfly larvae .
Web links
- Description of Eriosoma lanigerum at HortNET (English)
- Eriosoma lanigerum (Hausmann). In: Encyclopédie des ravageurs européens. HYPPZ, archived from the original on October 20, 2011 ; accessed on February 23, 2013 .
- Virginia Tech, Department of Entomology (English)
- Celeste Welty, Janet Murphy: Woolly Apple Aphid. In: Extension Fact Sheet HYG-2208-94. Ohio State University, archived from the original on December 23, 2014 ; accessed on July 10, 2020 (English).