Common spider mite
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Common spider mite ( Tetranychus urticae ) |
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| Tetranychus urticae | ||||||||||||
| Koch , 1836 |
The common spider mite or bean spider mite ( Tetranychus urticae ) is a species from the family of spider mites (Tetranychidae) within the mites (Acari).
features
Adult animals are very variable in terms of their size depending on their nutritional status. Females are about 0.4 to 0.6 mm in length, males 0.3 to 0.45 mm. The ellipsoid , soft-skinned animals have a convex upper side and are flattened below. During the growing season they have a transparent, light to brown-green color with two distinct, blurred, large, dark lateral spots that are formed by the translucent blind sacs of the midgut. From late summer to the following spring, the hibernating females are colored orange-red to vermilion. With the exception of the six-legged first larval stage, all developmental stages have eight walking legs.
biology
The common spider mite overwinters exclusively in the form of the orange-red "winter females", which emerge from late summer when the daylight decreases. They can be found in colonies in all sorts of sheltered places in winter, such as fallen leaves, on herbaceous plants, under the bark of woody host plants, etc. The ability of females to withstand extremely low temperatures is enormous. In this way, they can survive continuous temperatures of −15 ° C for a few weeks. In spring, when the temperature rises, the females start eating again, change into the greenish-transparent summer form and then lay eggs again. The resulting offspring then colonize their host plants again in the course of the vegetation period. Under suitable conditions, they quickly develop into colonies there, in which all stages of development of the species are found: From the yellowish-transparent, round eggs (diameter approx. 0.13 mm) hatch a six-legged, maximum 0.2 mm long, greenish-transparent larva. This is followed by a legless larval resting phase (protochrysalis), from which the first nymph stage (protonymph) arises after a molt. At this stage the animals have eight legs. After the second resting phase (deutochrysalis), the second nymph stage (deutonymph) hatches, from which the adult animal (imago) emerges after the last resting phase (teliochrysalis). The duration of the entire ontogenesis is about 10 to 30 days, depending on the temperature.
The adult females produce around 50 to 100 eggs in the course of their two to five weeks of life. Which gender develops from the respective egg is determined by fertilization: unfertilized eggs that contain only one set of chromosomes , i.e. are haploid , always develop into haploid males, while fertilized, diploid eggs always develop into females. This phenomenon is called arrhenotocia . Unmated females consequently only produce parthenogenetically male offspring, while both males and females can develop from the eggs of mated females, depending on whether the respective egg was fertilized during mating. These relationships also result in a self-regulation of the gender ratio of a population: If there is a shortage of males, more females remain unmated and consequently produce more males again, while an excess of males leads to significantly more females in the next generation. In a normal population, the male to female ratio is typically between 1: 3 and 3: 4.
Under good living conditions, i.e. H. In a dry, hot climate, the life cycle of the common spider mite takes place relatively quickly, so that an adult female can emerge from a deposited egg within about a week . This explains the extraordinary growth potential and the explosive population development of the species at high temperatures, such as those in Central Europe sometimes in August. In total, there are usually six to nine generations per year.
Host plants and distribution
The polyphagous species , which occurs worldwide with the exception of the Antarctic, is the spider mite with the greatest economic importance as a pest . In Germany, the common spider mite is found on around 90 cultivated plants, including vines , beans , peas , cucumbers , hops , potatoes , strawberries , sunflowers and fruit trees such as apples , pears , plums and gooseberries . More than 200 host plants are attacked worldwide, including, for example, cotton , hemp , cassava and soy as important crops.
Damage and damage
The common spider mite pricks the lower epidermis and the sponge parenchyma up to the chloroplast-rich cells of the palisade parenchyma with its mouthparts from the underside of the leaf in order to suck up the sugar-containing cell sap as well as the chloroplasts themselves. Since it can perform 18 to 22 punctures per minute, the protective cuticle of the plant is severely attacked and its protective effect against uncontrolled gas exchange is reduced. As a result, the cells collapse relatively quickly. This results in a physiological reaction of the plant, which leads to increased water absorption and increased perspiration . The transpiration rate soon exceeds the water absorption, so that severely infected leaves slowly dry up. Small, light, yellowish-white spots appear on the leaves when infected. Leaves that are more severely affected will necrote , change color from green to gray or copper brown, and eventually fall off. In the case of hops, this damage is therefore called "copper burn". With more severe infestation, fine webs develop on the plants, especially on the underside of the leaves, but also on the shoots.
Photo gallery
Combat
The common spider mite represents a serious economic problem in many agricultural crops as well as in horticulture. Accordingly, a sufficient number of approved and effective synthetic acaricides for combating spider mites are available in most countries . Of course, the use of these funds should only take place if he z. B. after reaching a certain control threshold makes technical and economic sense. In addition, only acaricides that are gentle on beneficial organisms should be used, since the common spider mite also has a number of natural opponents that can also control the population development of the spider mites. These are, in particular, predatory mites (Phytoseiidae), flower bugs (Anthocoridae), the black ball ladybug Stethorus punctillum (or other species of this genus outside Europe) as well as diurnal species (Hemerobiidae) and lacewings (Chrysopidae). When using plant protection products that are gentle on predatory mites, you usually do not need to fight the spider mites yourself, as beneficial organisms hold back their development so much that they no longer cause economic damage.
Synonyms
The large number of synonyms under which the species has been described over time is noteworthy:
- Tetranychus aduncus Flechtmann & Baker, 1967
- Epitetranychus aequans Zacher, 1916
- Epitetranychus alceae Oudemans, 1928
- Tetranychus althaeae from Hanstein, 1901
- Tetranychus arabicus Attiah, 1967
- Tetranychus aspidistrae Oudemans, 1931
- Tetranychus bimaculatus Harvey, 1892
- Epitetranychus caldarii Oudemans, 1931
- Tetranychus choisyae Oudemans, 1931
- Acarus cinnabarinus Boisduval, 1867
- Acarus cucumeris Boisduval, 1867
- Eotetranychus cucurbitacearum Sayed, 1946
- Tetranychus dahliae Oudemans, 1937
- Tetranychus dugesii Cano y Alcacio , 1886
- Tetranychus eriostemi Murray, 1877
- Acarus ferrugineus Boisduval, 1867
- Tetranychus fervidus Koch, 1841
- Tetranychus fici Murray, 1877
- Tetranychus ragariae Oudemans, 1931
- Tetranychus fransseni Oudemans, 1931
- Epitetranychus hamatus Zacher, 1916
- Acarus hematodes Boisduval, 1867
- Tetranychus inaequalis Targioni Tozzetti, 1878
- Eotetranychus inexspectatus Andre, 1933
- Tetranychus longitarsus Donnadieu, 1875
- Tetranychus major Donnadieu, 1875
- Tetranychus manihotis Oudemans, 1931
- Tetranychus minor Donnadieu, 1875
- Tetranychus multisetes McGregor, 1950
- Tetranychus piger Donnadieu, 1875
- Distigmatus pilosus Donnadieu, 1875
- Tetranychus plumistoma Donnadieu, 1875
- Tetranychus reinwardtiae Oudemans, 1930
- Tetranychus ricinus Saba, 1973
- Acarus rosarum Boisduval, 1867
- Tetranychus russeolus Koch, 1838
- Acarus sambuci cupboard, 1781
- Eotetranychus scabrisetus Ugarov & Nilolskii, 1937
- Tetranychus stellariae Oudemans, 1931
- Acarus telarius Linnaeus, 1758
- Acarus textor Fourcroy, 1785
- Tetranychus viburni Koch, 1838
- Tetranychus violae Oudemans, 1931
- Acarus vitis Boisduval, 1867
credentials
- ↑ Tetranychus urticae Koch 1836. Fauna Europaea, Version 1.3, April 19, 2007 , accessed on October 4, 2007 .
