The Asian lady beetle has been attracting attention for several years. There are reports of desperate residents who are helplessly exposed to the plague in winter. Studies have so far given no indication that the Asian species is killing off domestic relatives.
Asian ladybird – pest or beneficial?
The Asian lady beetle is a prime example of the fine line between harmful and beneficial insects. Towards the end of the 20th century, the species was imported to Europe because, due to its great hunger for aphids, gardeners hoped for targeted and efficient control of the pest.
Actually, the supposed beneficial insect was only released in greenhouses. But the ladybug found its own way into the wild. Since then, the species has spread unhindered throughout Europe because it has no natural predators here.
Conservationists fear that the Asian lady beetle will displace the native seven-spot lady beetle.
No signs of extinction
In some regions the introduced species is more common than the native seven-spot ladybird and it is not uncommon for it to become a plague. Nevertheless, field studies have failed to provide any evidence that the invasive species is eradicating native ladybirds. The seven-spot ladybird is also very competitive and is an invasive species in North America. In studies in 2013, this species was more common in wine-growing regions than its Asian relative. But that varies from region to region.
Pest controller with variable food spectrum
The seven-spot ladybird can eat around 50 aphids per day, while its Asian relative can kill up to 270 aphids in one day. Therefore, its role as a biological pest controller is extremely important. The Asian lady beetle is not particularly picky about its prey. Even the toxins secreted by elderberry aphids do not bother the robust species.
If there are no aphids, the Asian lady beetle changes its diet and preys on other soft-skinned insects, eggs and larvae. It feeds on gall midges, butterflies and is dangerous for native ladybird species. The beetle also doesn't stop at its own kind. When food is scarce, both larvae and adults become aggressive and kill their counterparts through bites.
Asian ladybird as an opponent:
- kills blood lice
- reduces populations of the mealy apple aphid
- eats hop lice on a large scale
- frees grapevines from phylloxera
Asian lady beetles are used for pest control
Unfoundedly feared in viticulture
In the fall, the aphid colonies slowly decline, so the Asian lady beetle has to adapt to other food sources. It uses the high sugar content of grape juice as an energy source. Fruit that has already been damaged magically attracts the beetles. Grape varieties that tend to crack and ripen very late are therefore particularly at risk.
The beetles get into wine production through the grape harvest. It is now known that the bitter-tasting hemolymph of the beetles has a negative effect on the aroma of wine. Pyrazines represent the main component responsible for this taste impairment. However, studies have shown that the impact on taste is less than feared. For the Riesling grape variety, the wine's recognizable taste threshold is four to five beetles per kilogram. For Pinot Noir, this threshold is between three and six beetles per kilogram.
The same number of native species causes a significantly greater taste change in wine. The hemolymph substance also occurs naturally in the Merlot, Cabernet Sauvignon and Sauvignon Blanc grape varieties. The so-called ladybird tone is only undesirable for the quality wine varieties Riesling, Pinot Noir and Müller-Thurgau.
Hardly any damage to fruit growing
In autumn, ladybugs feed on fruit
While the beetles appear as useful pest controllers on fruit trees in spring and summer, they transform into fruit eaters in autumn. During this time, the Asian lady beetle feeds on various types of pome and stone fruits. Significant feeding damage has so far only occurred sporadically. There are reports from Austria of a loss of quality in fruit growing. Taste changes may occur during the production of fruit juices.
Soft-skinned fruit is endangered:
- Ribes and Rubus: raspberries, blackberries, currants
- Malus and Pyrus: late-ripening apple and pear varieties
- Prunus: plum, apricot, cherry, peach
Highly effective bacterial inhibitors
Scientists discovered that the Asian lady beetle produces a natural antibiotic. This harmonin not only protects the beetle's immune system. It is also said to work against the pathogens that cause malaria and tuberculosis, which is why the suitability of harmonin as a medication is now being researched.
Excursus
This is how the Asian lady beetle secures a survival advantage
Asian ladybirds have an antimicrobial substance called harmonin. In addition, your immune system can defend itself against pathogens with over 50 different protein compounds. No other animal can produce so many antimicrobial peptides. The species is considered to be less susceptible to pathogens than the native beetles, which gives it a decisive selection advantage.
The beetles also use a kind of bioweapon because their hemolymph contains microscopic spores of a parasitic protozoan. These fungus-like organisms belong to the higher classification Nosema. In the body of the Asian lady beetle, the spores are inactive, so they do no further harm to the species. Researchers suspect that harmonin inhibits the proliferation of spores and thus keeps them at a safe level.
If a domestic ladybird eats the larvae or eggs of an infected beetle, the spores spread through its organism and multiply. The result is serious illnesses that are fatal. With this weapon, the introduced species displaces native representatives.
Is pest control useful?
The Asian lady beetle is multiplying rapidly and driving away native lady beetle species
Experts have not yet agreed on whether the Asian lady beetle needs to be destroyed. At least in Switzerland, the beetle has already displaced many native species. Here it is forbidden to intentionally release the Asian lady beetle into nature.
Be careful when sweeping away
If you want to remove the beetles from the apartment, you can use a hand brush and a dustpan. However, the beetles often feel disturbed. They defend themselves with so-called reflex bleeding and secrete a yellowish defensive secretion from their leg joints. The substance gives off an unpleasant odor and leaves yellow stains on carpets, floors, wallpaper and curtains.
Therefore, use a broom that is as soft as possible so as not to bother the animals unnecessarily. You can then release the beetles outside, where they die in winter due to freezing temperatures.
Soak it up
With the vacuum cleaner you can remove the bugs in a convenient way. However, their life in the vacuum cleaner bag ends painfully with slow suffocation. Use a fresh vacuum cleaner bag to save the animals this stress. You can then place the bag in the freezer so that the beetles freeze immediately.
Avoid chemical agents
An effective method for killing the beetles is to use contact insecticides. Agents containing pyrethrin or pyrethroid are fatal on contact. These are sprayed at the entrance gates of the wintering quarters and only take effect when the beetles overcome the barrier. However, such insecticides are problematic because they are harmful to he alth and do not have a selective effect. Beneficial insects can also die if they come into contact with the poison.
Profile
Asian ladybirds have significantly more points (usually 19) than European ladybirds (usually 7)
Harmonia axyridis reaches a size of between six and eight millimeters and is five to seven millimeters wide. The species is characterized by an extremely variable body color, ranging from light yellow to dark red. The cover wings are dotted black.
There are usually 19 points, some of which can be completely fused together, weakly developed or completely missing. In some beetles it appears as if the cover wings are colored black and spotted with red. This characteristic earned the species the nickname multicolored ladybird or harlequin ladybird.
Neckshield:
- light yellow colored
- black M or W-shaped drawing
- Pattern can cover the entire pronotum
Dissemination – in Europe and around the world
The natural habitat of this species extends across East Asia. The beetle is found in China and inhabits habitats as far south as Yunnan and Guangxi. Further distribution areas are in Japan, Korea and Mongolia as well as in the east of Russia. The species has been used as biological pest control in many areas since 1916, which is why the species can now be found worldwide. There seems to be a particularly high density of individuals near cities.
Identifying larvae
Very young larvae are initially yellow-green in color and have black bristles. Later the basic color darkens to blue-gray or black. Her body is covered in bristles. These so-called scoli have two to three branches. The orange-colored side areas, which become apparent during larval development, are striking. The coloring extends over the first five segments of the abdomen. The fourth and fifth abdominal segments also have an orange bristle on both sides.
Differences between Asian and European ladybirds
There are around 250 species of ladybirds in Europe, 82 of which are native to Germany. They inhabit different habitats where there are enough aphids. This great diversity, combined with the variability in body coloration and spot pattern, makes identifying the species difficult. The most common native species can be easily identified by a few characteristics. The color of the pronotum is important in the Asian lady beetle.
| Size | Basic color | Drawing | |
|---|---|---|---|
| Two-spotted ladybug | 3.5 to 5.5 millimeters | red or black | two black or two to three red dots |
| Seven-spotted ladybug | 5, 2 to 8 millimeters | red | seven black dots, two white spots on the pronotum |
| Thirteen-spot ladybug | 5 to 7 millimeters | red, sometimes completely red or black | thirteen black dots |
| Dry Grass Ladybug | 3 to 4 millimeters | black | yellow dots |
| Sixteen-spot ladybug | 2.5 to 3.5 millimeters | light yellow | numerous black spots |
Lifestyle and development
The Asian lady beetle can live up to three years. The beetles usually reach an age of between one and three months. Its development depends on environmental conditions and food availability. Although the beetles are often viewed as a pest, not all individuals survive.
Mating
Asian lady beetles mate in spring
As soon as the first rays of sun warm the earth in late winter and melt the snow, the beetles come out of their winter quarters and look for a suitable mating partner. Copulation can last between 30 minutes and 18 hours. The female usually mates with several males, sometimes visiting up to 20 partners. Mild temperatures influence the development of populations. Under optimal conditions, the species is capable of producing several generations per year.
Offspring per year:
- Great Britain: two generations
- Greece: four generations
- Asia: five generations
Egg laying
A female can lay between 1,800 and 3,500 eggs in a lifetime. It selects plants that are infested with aphids. The females attach their yellowish eggs to the leaves in small packets of 20 to 30. Not all eggs hatch into larvae, as many fall victim to unfavorable weather conditions or hungry insect eaters. After three to five days, the larvae of the remaining eggs hatch.
Larval development
The larvae need two weeks to fully develop into ladybirds. During this time, the offspring can eat up to 1,200 lice. They molt three times and then pupate directly on the leaf. The pupa usually rests openly on the top of the leaf. After five to six more days the imago hatches.
Wintering
In their natural home, the beetles spend the cold season in crevices. They fall into hibernation and do not eat any food. In Central Europe, the animals form large colonies on house walls in which they search for suitable winter quarters.
A secreted scent causes the beetles to come together in large numbers. They look for suitable cracks and crevices where they are safe from frost. It is not uncommon for insects to get lost in apartments and houses. However, they do not pose a danger to the buildings.
Dangers and challenges
Despite the advantages that the Asian lady beetle has over native species, it has to prove itself in nature. As conditions change, its survival advantage evens out. Scientists, on the other hand, are trying to help humanity with other means. Because the fact that the Asian lady beetle can no longer be displaced is a certain fact.
Enemies
One of the rare natural enemies is the forest guard. The stink bug is predatory and hunts for insects and their larvae. They pierce their powerful proboscis into the thin membranes between the segments because they cannot pierce hardened chitinous shells. They then suck out their victim on the spot or carry it impaled to a safe place. However, the forest guard cannot manage to contain the populations of the Asian lady beetle alone.
Climate Change
The native seven-spot ladybird has been massively displaced by its Asian relative in recent years. As temperatures rose, the native species was able to recover, contrary to the dire fears of conservationists. Studies have shown that domestic beetles gain significantly more weight at higher temperatures than their Asian competitors.
If the temperature rises on average by three degrees Celsius, then both species of ladybirds eat more than under normal temperature conditions. While the fat content and body mass of the seven-spot lady beetle increase, the development of the Asian lady beetle stagnates. The species pursue different strategies when it comes to energy use. The seven-spot ladybird saves its energy reserves for hibernation, while the Asian ladybird invests all its energy in producing offspring.
This results in extreme mass proliferation of the Asian representative in years with particularly hot summer months. However, many of them do not survive the freezing temperatures. These results show that at least the Asian beetle does not benefit from climate change.
Wingless breeding
French researchers have bred genetically modified versions of the Asian lady beetle. These individuals do not develop wings and therefore cannot spread uncontrollably. In France, these cultivars are marketed as biological pest control. However, there is definitely a risk that the specimens will cross with wild ladybirds. The offspring can certainly develop wings again.
Preventing the spread
Ladybugs get inside through the smallest cracks
The most effective way to prevent Asian lady beetles from getting into your house and apartment is thorough prevention. Prevent the beetles' access by repairing cracks and damage to the facade. Even the smallest gaps are enough for insects to get into the building. Roof overhangs and supply pipes, as well as windows and doors, can be equipped with insect screens.
Are ladybug houses effective?
Insect hotels are available in stores that are specifically designed for ladybugs. Their primary purpose is to provide native species with safe shelter for overwintering. Therefore, they are equipped with warming material and are placed in a protected location.
The insect hotels are occasionally recommended as a shelter for the Asian lady beetle. If there are large colonies on the walls of the house, a ladybird house is unlikely to help. The beetles will still look for suitable gaps in the facade or cracks in doors and windows.
Fragrances
So far there is hardly any reliable knowledge about effective substances for attracting or deterring. Affected homeowners repeatedly report that camphor and menthol have a deterrent effect on adult Asian lady beetles. However, the duration of the effect of the plant secondary substances is short-lived, which is why the measure must be constantly renewed.
Tip
So that the insects don't get into the apartment, you can place cut vanilla pods or bay leaves on the windowsill.
Remove damaged fruit
The Asian lady beetle changes its diet in the fall when the aphid colonies slowly perish. They then feed on sugary fruit juices. Damaged and eaten soft-shelled fruit is particularly attractive to the beetles. Therefore, check your garden and remove such fruits in good time.
Control in viticulture and fruit growing
Contamination of wines and fruit juices by ladybirds cannot be completely eliminated afterwards. You should therefore check the trees and vines for possible infestation about two weeks before the planned harvest. Glued yellow boards are ideal for carrying out inventory control. If necessary, the insects can be shaken off by hand before processing the fruit.
Tip
Oak chips or activated charcoal weaken the ladybird tone in wine.
Frequently asked questions
Is the Asian lady beetle poisonous?
Although the beetle emits a bitter substance as a defense against enemies that smells unpleasant, the species poses no danger. It is not poisonous to dogs, cats or humans.
It can happen that the animals are crushed by the grape harvest in wine production. This also means that the bitter substances get into the wine, where they can cause changes in the taste. However, this so-called ladybird tone is not harmful to he alth, but rather reduces the quality of the wine. Some grape varieties naturally contain the same substance that was discovered in the beetle's defensive secretion.
Can the Asian lady beetle bite?
If the beetles get into a stressful situation, so-called reflex bleeding occurs. They secrete a white to yellowish substance that is intended to act as a deterrent. When panicked, the Asian lady beetle is also capable of biting. However, a bite is hardly painful and completely harmless to humans.
How dangerous is the Asian lady beetle for the ecosystem?
So far, researchers do not agree on whether the invasive species can actually eradicate native ladybirds. There were repeated periods when the introduced beetle appeared in large numbers and was superior to the seven-spot ladybird. Under changing environmental conditions, the populations of the Asian representative declined again in favor of the native beetles. In many places, however, the unwanted species is more common than the original beetles.
Ladybirds can be found worldwide and can survive in different climate zones. However, they have a great benefit because they keep various plant pests at bay. This makes it difficult to clearly classify the Asian lady beetle as a pest or beneficial insect.
How can the Asian lady beetle compete?
The species has decisive survival advantages over native ladybirds. Researchers discovered an antibacterial substance in the hemolymph and around 50 different protein compounds. This allows the organism to effectively defend itself against pathogens. The Asian lady beetle is less susceptible to disease than the native seven-spot lady beetle.
Another sensation is the existence of microspores of the Nosema type. The beetle organism keeps the spores at a safe level. If the beetle is eaten by a predator, the spores spread throughout its body. Infection causes death in other insects.
Where does the Asian lady beetle come from?
The beetle's original homeland is in East Asia. There the species was used effectively as a biological pest controller. For this reason, it was transported to America in the 20th century, where it was used in greenhouses to combat pests. This example was followed in Europe. However, it could not be guaranteed that the species does not reproduce independently outside the greenhouses.
In 2001, the first free-living specimen of an Asian lady beetle was found in Belgium. Since then, the species has spread en masse throughout Europe. This development can no longer be reversed because there are no natural enemies.
