Lid scale lice
| Lid scale lice | ||||||||||||
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Lid scale lice |
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| Systematics | ||||||||||||
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| Diaspididae | ||||||||||||
| Maskell , 1878 |
The lid scale insects (Diaspididae) are a family of the scale insects (Coccoidea). With over 2600 known species worldwide, they are the largest and most specialized family of scale insects. Many of them are economically important pests . Europe is home to 213 species.
features
As with many plant lice , there is also a clear sexual dimorphism between the males and females of the cap scale insects . Males are very small and delicately built and usually have a pair of front wings. Their hind wings are reduced to holders . In some species the males are wingless or even have a larva-like shape. They have no mouthparts and their genitals are on the outside and therefore easily recognizable. They are very long so that they can get under the shield to the genitals of the females. The males' antennae are well developed as the females secrete pheromones that attract the males. So far, the morphological differences between the various species in the males have not been investigated, so that it is not possible to determine the genus on the basis of the males.
The females are very different in their appearance depending on the species. Their larva-like body shape varies from round to oval to elongated, with the animals being flattened to different degrees. The body length of the wingless females usually measures between 0.9 and 1.5 millimeters. The segmentation of the body is visible to different degrees, the last four or five of the eight to nine abdominal segments are sclerotized and fused together to form pygidium and the head is usually fused with two or three thorax segments . Compound eyes are either very small or absent, as are the legs . The antennae are also stunted. The shield of the lid scale insects completely covers the body, but it is characteristically not connected to it, but just lies over it like a bowl. The shield is formed by glandular secretions on the back, especially on the pygidium. The excreted silk threads are connected to another secretion from the Malpighian vessels and condensed. The shield, which has hardened after a while, has a yellow, brown or black color depending on the type. The color is often specific to a genus, but like its shape it can differ depending on the food plant, stage of development and living conditions in the same species, which makes it very difficult to identify the species. After moulting, the exuvia that have been rejected are incorporated into this shield, which is expanded by glandular secretions in addition to the growth of the animals in attached layers. In females, the first two exuvia are usually incorporated, in males it is only the first because their shield is not enlarged after the second larval stage. Depending on the type, this is done in different positions. In addition to the dorsal shield, a much weaker shield is also formed on the ventral side.
The adult females can be distinguished from the larvae in the second stage by the fact that in the former the genital opening is recognizable between the seventh and eighth segment and they sometimes also have disc-shaped structures on the ventral side of the pygidium, on which the glands secrete their wax secretions.
Way of life
Lid scale lice are only mobile in the first stage and look for a suitable place above ground on the plant where they can settle down to suck up plant sap. Unlike the other representatives of the scale insects, the lid scale insects do not produce honeydew , which is why they cannot enter into symbioses with ants . In the first stage, the lice often climb up on the plants and then let the wind carry them to new food plants. Not infrequently, however, the animals are also spread by transport to birds, insects or other animals ( phoresy ). Successful resettlement is primarily linked to medium to high humidity, while drought and heavy rain usually kill the animals.
From the second larval stage, the female cap scale insects are sedentary and no longer have any legs. The second stage represents the most important feeding stage. In the third and adult stage, the females also suck plant sap and reproduce. The two-sex mating takes place soon after the last moult. The males only eat in the first and second instar, after which they cannot eat because of the stunted mouthparts. When the male adults hatch out of the pupa below the shield, they go in search of females. They are only very short-lived and therefore rarely observed.
Reproduction and development
Most lid scale insects reproduce in two sexes, but parthenogenesis can also be observed. In purely parthenogenetically reproducing species there are only female individuals. Very few species are viviparous and give birth to living larvae; most lay eggs ( oviparia ), with usually 50 to 150 of them being laid by a female during their lifespan; 1 to 10 per day. In some species, in the extreme, either only about 10 or more than 600 eggs are laid in total. The eggs are laid below the female's protective shield. Females go through two larval stages and do not pupate, in males the two larval stages are followed by the prepupal and pupal stage, after which the male imago hatches .
Types (selection)
The family of the cap scale insects includes (as of April 25, 2019) 2625 species, which are distributed over 429 genera.
- Aulacaspis yasumatsui
- Chionaspis salicis
- San José scale insect ( Comstockaspis perniciosa )
swell
Individual evidence
- ↑ Diaspididae. Fauna Europaea, accessed January 7, 2008 .
- ↑ Diaspididae . García Morales M, Denno BD, Miller DR, Miller GL, Ben-Dov Y, Hardy NB. 2016. ScaleNet: A literature-based model of scale insect biology and systematics. Database. doi: 10.1093 / database / bav118 , http://scalenet.info . accessed on April 25, 2019
Literature and web links
- Hans Strümpel: Homoptera (plant teat). Manual of Zoology 4 (28) , Walter de Gruyter. Berlin, New York 1983, ISBN 3-11-008856-8
- Arthropods of Economic Importance (English)
