Two-point ladybug
| Two-point ladybug | ||||||||||||
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Two-spot ladybird ( Adalia bipunctata ) |
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| Adalia bipunctata | ||||||||||||
| ( Linnaeus , 1758) |
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The two-point ladybird or just two-point ( Adalia bipunctata ) is a beetle from the ladybird family (Coccinellidae).
features
Two points are 3.5 to 5.5 millimeters long. The body is oval, but more round than oblong. The legs are black. The antennae are quite short and thicken slightly at the end. There are two variants of the coloring that have nothing to do with the sex or age of the animals. The first variant has a red basic color, there is a black point on each wing cover. The thorax is yellow with a black spot in the middle. Variant number two is almost entirely black, but here you can see two to three red dots on each wing cover. Around 15 percent of the beetles are colored this way. In addition to the genes , environmental influences also play a role in the coloration of the beetles. The red forms survive winter better, but the black ones are more active when reproducing.
Way of life
Ladybugs belong to the cold-blooded ( poikilothermal ) animals, ie their body temperature depends primarily on the ambient temperature. However, the light can change the body temperature. If you illuminate ladybugs, their body temperature rises because some of the light is absorbed and converted into heat. Body parts colored black absorb more strongly than body parts colored red. When illuminated, the body temperature of the black variant is approx. 5.5 ° C, that of the red variant approx. 3 ° C above the ambient temperature of 18 ° C. Metabolic activity increases with body temperature. The black variant therefore has a higher nutritional requirement in order not to starve.
In winter, the increased metabolic activity means a disadvantage, as black ladybugs use up their fat reserves more quickly and starve to death more easily than the red ones. The ladybugs feed on their fat reserves during rigid winter. In spring it is predominantly red individuals who wake up from winter rigor, since winter mortality is greater than that of the red form due to the higher metabolism of the black form.
This is a good example of natural selection , as a directed process that leads to more adaptation of living things to their environment. The red form of the ladybird is recessive , the black, multiple alleles determine the extent of the black spots. If the environmental conditions change, however, the better adapted variants can reproduce more successfully so that the population is not endangered (cf. fitness (biology) ). The variability forms a genetic reserve for the species and has great evolutionary significance. Each population (red and black) produces more offspring than can survive. If one considers the frequency of the black and red ladybirds, the red individuals clearly predominate in their frequency in spring. In autumn, however, the black ladybirds dominate their population. Apparently the black individuals have better conditions in the warmer months, so they are more adapted to their environment than the red ladybugs. In winter, the metabolic activity of the ladybirds decreases, they hibernate by falling into winter rigor in sheltered places and feeding on the fat stores they have built up in summer. Without the red ladybirds with the lower metabolism, these ladybird species would be threatened with extinction (see balanced polymorphism ). The black ladybirds have a dominant allele in their genotype, while the red color of the elytra is recessive in inheritance. As a result, the number of black ladybugs increases in the warm months when they can also be active earlier in the day due to their higher heat absorption. They reach the correct "operating temperature" earlier and have more time for reproduction. The diversity of the environment, in this case the temperature and the light radiation, selects the ladybirds with different wing cover colors, thus preserving or “balancing” the differently shaped, polymorphic characteristic.
Occurrence and distribution
The beetles are very widespread in Europe and Asia and were also introduced to North America , and subsequently spread to Central America . They live in gardens, forests and hedges, but also come into houses in autumn to overwinter there. If you find one in the apartment in winter, you should put it in a cold place (attic). Frost does not harm them. If they stay in the warm during the winter, they will die. Usually overwintering takes place under bark and moss.
Adalia bipunctata , along with Coccinella septempunctata, was one of the two most common ladybird species in Europe, but their populations have declined particularly sharply since the introduction of the invasive species Harmonia axyridis . In contrast to Harmonia axyridis, Adalia bipunctata has no immune defense against the microsporidia harbored by it in the hemolymph . According to the entomologists Jens Esser from the Entomological Society ORION and Werner Schulze from the Naturschutzbund Deutschland , the species is facing extinction in Germany.
Way of life
The diurnal animals actively crawl around on leaves looking for aphids and leaf fleas, so they are very useful for the gardener. After mating, the female lays the eggs on a plant that is usually located near an aphid colony. The larvae live and feed similarly to the adult animals. The pupae usually hang from the underside of a leaf. The fully developed beetles hatch from the pupae.
Reproduction
When these animals reproduce, surprisingly 80 to 90 percent of the offspring are female. Scientific research has shown that this is due to symbiotic bacteria that live in the sex cells of the females. These preferentially promote the union of two X chromosomes and thus the conception of a female. Furthermore, researchers from the University of Western Australia in Perth found out in 2005 that the Adalia bipunctata are at high risk of contracting a sexually transmitted disease due to their promiscuity . Over 90 percent of the ladybirds in a colony can become infected in the course of a summer.
After wintering, ladybugs begin to mate diligently in the spring. The beetles change their partners every two days and are among the most mating insects. The mite Coccipolipus hippodamiae , which makes female ladybugs sterile , is also transmitted during sexual intercourse . However, this does not happen until three weeks after the infestation, so there is still enough time to lay eggs.
Use in pest control
Two points are bred commercially and used as beneficial insects to control aphids in organic farming and horticulture .
literature
- Harde, Severa: Der Kosmos Käferführer, The Central European Beetles , Franckh-Kosmos Verlags-GmbH & Co, Stuttgart 2000, ISBN 3-440-06959-1
- Jiři Zahradnik, Irmgard Jung, Dieter Jung et al .: Beetles of Central and Northwestern Europe. Parey, Berlin 1985, ISBN 3-490-27118-1
Web links
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Individual evidence
- ↑ Peter MJ Brown, Robert Frost, Julian Doberski, Tim Sparks, Richard Harrington, Helen E. Roy: Decline in native ladybirds in response to the arrival of Harmonia axyridis: early evidence from England . Ecological Entomology 36 (2), 2011, pp. 231-240.
- ↑ Helen E. Roy, Tim Adriaens, Nick JB Isaac, Marc Kenis, Thierry Onkelinx, Gilles San Martin, Peter MJ Brown, Louis Hautier, Remy Poland, David B. Roy, Richard Comont, René Eschen, Robert Frost, Renate Zindel, Johan Van Vlaenderen, Oldřich Nedvěd, Hans Peter Ravn, Jean-Claude Grégoire, Jean-Christophe de Biseau, Dirk Maes: Invasive alien predator causes rapid declines of European ladybugs . Diversity and Distributions 18, 2012, pp. 717-725.
- ↑ Jens Esser, Andreas Vilcinskas and Werner Schulze, quoted in a dpa report, ladybugs with two dots are becoming increasingly rare. Die Welt, May 8, 2017.
- ↑ Gregory DD Hurst, Rosie G. Sharpe, Angela H. Broomfield, Linda E. Walker, Tamsin MO Majerus, Ilia A. Zakharov, Michael EN Majerus (1995): Sexually transmitted disease in a promiscuous insect, Adalia bipunctata . Ecological Entomology 20, pp. 230-236.
- ↑ K. Mary Webberley, Jarosław Buszko, Valerie Isham, Gregory DD Hurst (2006): Sexually transmitted disease epidemics in a natural insect population . Journal Of Animal Ecology 75 (1), pp. 33-43.
- ↑ Adalia bipunctata (two-point ladybug). In: Oekolandbau.de (information portal of the Federal Agency for Agriculture and Food ). November 25, 2010, accessed on June 4, 2019 (German).