Silver fir shoot louse
| Silver fir shoot louse | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Dreyfusia nordmannianae | ||||||||||||
| Eckstein , 1890 |
The silver fir tree louse ( Dreyfusia nordmannianae , syn .: Adelges nordmannianae , Dreyfusia nüslini C. B. ), also called one-brood fir tree louse , is a species of plant louse from the Adelgidae family .
description
The silver fir shoot grows 1 to 3 millimeters in size and is dark in color. There are wax edges on the sides of the body and a wax comb on the middle of the back. Both winged and wingless specimens occur. The newly hatched young larvae are around 0.4 millimeters in size. The eggs are rusty brown.
Similar species
The silver fir tree louse can be confused with the native pine stem louse ( Adelges piceae ) and with the European silver fir tree louse ( Mindarus abietinus ). The fir stem louse attacks the trunk bark of trees in the pole wood and tree wood age, while the European silver fir tree louse attacks the needles and bends them forward like tufts. Both species, like the silver fir shoot, also release wax wool.
distribution
The natural distribution area of the silver fir tree includes the higher elevations of the western Caucasus , the Crimea and the eastern Pontus Mountains . There it occurs mainly in pure and mixed stands of the Nordmann fir ( Abies nordmanniana ) at altitudes of up to 1400 meters. In the 1840s the species came to Central Europe through the import of Nordmann firs. By the 1920s and 1930s it had spread over the entire occurrence of the silver fir in Europe and largely displaced the native pine stem louse ( Adelges piceae ). The species came to North America through the import of the silver fir ( Abies alba ).
Life cycle
In the natural range, the Nordmann fir and the Caucasus spruce ( Picea orientalis ) serve as host plants. The silver fir shoot alternates between these two species during its two-year development. Five successive generations are formed during this development. The sexual and gall-forming generations attack the Caucasus spruce, which is the primary host. The adult animals of the gall-forming generation have wings and switch to the Nordmann fir as a secondary host. Several wingless generations develop on the Nordmann fir, the females of which can reproduce asexually. However, winged females also develop, which switch back to the Caucasian spruce. Since the Caucasus spruce does not occur in Central Europe and the Norway spruce ( Picea abies ) is not a suitable substitute, the development takes place in an annual cycle only on the silver fir. Only asexual generations are formed and development is slower on the white fir than on the Nordmann fir.
The larvae usually overwinter in the 2nd larval stage on the branch, trunk or shoot bark under conspicuous, white wax wool excretions. They can withstand temperatures as low as –20 ° C. In the following spring, during the first extended warm period, the larvae continue to develop and after the third moult, wingless females develop. The females begin to lay eggs at the end of March, which can extend into June. During this time, the female lays 100 to 500 eggs, which are attached in clump-shaped piles to the trunk bark and on the underside of annual shoots and covered with wax wool. The wax wool protects the eggs from drying out, moisture, cold and predators.
Two different types of young larvae usually hatch from the eggs from early to mid-May. Young larvae with long stinging bristles, so-called stem and shoot suckers, and young larvae with short stinging bristles, so-called needle suckers, appear. The trunk and shoot suckers suck on branch, trunk and shoot bark until autumn and do not shed their skin. There is also no reproduction. The needle aspirators are developing rapidly. While the older larval stages tend to be sedentary, the young larvae are characterized by their high mobility. They climb up to the young May shoots and suck on the undersides of young needles, causing the typical damage. Two different types of females develop from the needle suckers. The first type develops from the end of May and is winged. This type moves away from the original host tree and changes to the Caucasus spruce. In areas where the Caucasian spruce is missing, this type perishes. The second type is wingless and lays 10 to 30 eggs from June to the beginning of July in loose wax balls on the underside of the needles.
From mid-July to early August, young larvae hatch from these eggs and migrate to the branch, stem and shoot bark. There they join the trunk suckers and suckers and stay with them in a diapause until autumn . After shedding their skin in late September to mid-October, the larvae wrap themselves in wax wool and prepare to hibernate. The species spreads largely passively by the wind.
Harmful effect
The silver fir sprout attacks branches, trunks and shoots, more rarely May shoots, of young firs, which have a thin bark. Most of the trees that are sunlit and warm are populated. Trees from the age of around 30 are rarely infested. The first noticeable sign of an infestation are deformed Main needles, which curve mainly downwards. The sucking activity on the bark is mostly inconspicuous. If the infestation is severe, the May shoots can die off as early as the second year and the bark becomes cracked and pockmarked. In addition, the shoot bases thicken and the buds no longer sprout. The infestation can also drag on for years before the crown begins to die off from above. Sometimes the host tree succeeds in replacing the dead peak shoot with a still living branch. However, the tree is weakened by the infestation and is often attacked by secondary parasites.
Combat
Since no chemical agents are currently permitted in forest areas for combating silver pine shoots, only mechanical control is possible. In Christmas tree crops, however, control with insecticides is allowed and should be done shortly before or during budding. Heavily infested trees should be removed from the stand in winter and then burned. Trees weakened by the infestation should not be exposed too much. As a silvicultural measure, firs should only be rejuvenated under umbrella.
Individual evidence
- ↑ a b Entry on Arbofux.de accessed on June 27, 2010
- ↑ a b c d e f g h i j Dagmar Nierhaus-Wunderwald, Beat Forster: Increasing occurrence of the dangerous silver fir tree louse . In: Forest and Wood . No. 10 , 1999, p. 50-53 . [1]
- ↑ Georg Benz, Markus Zuber: The most important forest insects in Switzerland and neighboring countries . 1993, ISBN 3-7281-2357-9 , pp. 50-53 . [2]