Pest or beneficial insect?

the essentials in brief

• The Asian ladybird was introduced as a pest killer because it eats up to 5 times as many aphids a day as the seven-spotted ladybug.
• In some regions there are more Asian ladybirds than native seven-spotted ladybirds; however, it is believed that there is currently no risk of extinction.
• However, the Asian ladybird can harm the native when the food supply becomes scarce and it feeds on ladybird larvae.
• Whether or not the Asian ladybug should be controlled is a matter of dispute and has not been conclusively clarified; it does not pose a threat to fruit or vegetable growing.

Asian ladybug - pest or beneficial?

The Asian ladybug 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 gardeners hoped for a targeted and efficient control of the pest due to its great hunger for aphids.

The supposed beneficial organism was actually only released in greenhouses. But the ladybird has found its own way into the wild. Since then, the species has spread unhindered across Europe, as it has no natural predators here.

No signs of extinction

In some regions, the introduced species is more common than the native seven-spotted ladybird and it is not uncommon for the plague to occur. Nevertheless, field studies have not been able to provide any evidence that the invasive species is wiping out native ladybugs. The seven-spotted ladybug is also very competitive and is an invasive species in North America. In studies in 2013, this species was found more frequently in the wine-growing regions than its Asian relatives. But that differs from region to region.

Pest control with a variable food spectrum

The seven-point ladybird can eat around 50 aphids per day, while the Asian relative can kill up to 270 lice in one day. Thus, its role as a biological pest controller is extremely important. The Asian ladybug is not particularly fussy about its prey. Even the toxins secreted by elderberry aphids do not disturb the robust species.

In the absence of aphids, the Asian ladybird changes its diet and prey on other soft-skinned insects, eggs and larvae. It feeds on gall midges, butterflies and becomes dangerous for native ladybird species. The beetle does not stop at other species either. When food is scarce, both larvae and adult ladybugs are aggressive and kill their counterparts with bites.

Asian ladybug as an opponent:

• kills blood lice
• decreases populations of the mealy apple aphid
• eats hop lice on a large scale
• frees grapevines from phylloxera

Asian ladybugs are used for pest control

Unfounded feared in viticulture

Against the aphid colonies in autumn, the Asian ladybird has to adjust to other food sources. It uses the high sugar content of the juice from grapes as an energy source. The beetles magically attract the beetles that have already been damaged. Therefore, grape varieties that tend to pop and ripen very late are particularly at risk.

The beetles enter wine production with the grape harvest. It is now known that the bitter-tasting hemolymph of the beetle negatively affects the aroma of wine. Pyrazines are the main component responsible for this taste impairment. Studies have shown, however, that the taste effects are less than feared. In the case of the Riesling grape variety, the taste-recognizable threshold of the wine 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 change in taste in wine. The substance of the hemolymph also occurs naturally in the grape varieties Merlot, Cabernet Sauvignon and Sauvignon Blanc. Only in the quality varieties Riesling, Pinot Noir and Müller-Thurgau is the so-called ladybird tone undesirable.

Hardly any damage in fruit growing

In autumn, ladybugs feed on fruit

While the beetles appear as useful pest killers on fruit trees in spring and summer, they turn into fruit-eaters in autumn. During this time, the Asian ladybird feeds on various types of pome and stone fruit. Significant feeding damage has so far only occurred sporadically. There are reports from Austria of quality losses in fruit growing. Taste changes can occur in the production of fruit juices.

Soft-skinned fruit is at risk:

• Ribes and Rubus: Raspberries, blackberries, currants
• Malus and Pyrus: late ripening apple and pear varieties
• Prunus: Plum, apricot, cherry, peach

Highly effective bacteria inhibitor

Scientists found that the Asian ladybug produces a natural antibiotic. This harmonine not only protects the beetle's immune system. It should also work against the pathogens of malaria and tuberculosis, which is why the suitability of harmonin as a drug is now being researched.

Digression

This is how the Asian ladybird secures a survival advantage

Does pest control make sense?

The Asian ladybird reproduces rapidly and drives off native species of ladybirds

Experts have not yet agreed on whether the Asian ladybird needs to be destroyed. In Switzerland at least, the beetle has already displaced many native species. Here it is forbidden to consciously release the Asian ladybird into nature.

Be careful when sweeping away

If you want to remove the bugs from the apartment, you can use a hand brush and dustpan to help. However, the beetles often feel disturbed. They defend themselves with the so-called reflex bleeding and secrete a yellowish defense secretion from the leg joints. The substance gives off an unpleasant odor and leaves yellow stains on carpets, floors, wallpaper and curtains.

You should therefore use a broom that is as soft as possible so as not to unnecessarily bother the animals. You can then leave the beetles outside, where they die in winter from freezing temperatures.

Soak up

The vacuum cleaner is a convenient way to remove the bugs. However, their life in the vacuum cleaner bag ends in agony with slow suffocation. Use a fresh vacuum cleaner bag to spare the animals this stress. You can then put the bag in the freezer so that the beetles freeze to death immediately.

Refrain from chemical agents

One effective way to kill the beetles is to use contact insecticides. Agents containing pyrethrin or pyrethroid are fatal on contact. These are sprayed onto the entrance gates of the wintering roosts and only take effect when the beetles overcome the barrier. Such insecticides are problematic, however, because they are harmful to health and do not have a selective effect. Useful insects can also die on contact with the poison.

Characteristics

Asian ladybugs have significantly more points (mostly 19) than European ladybugs (mostly 7)

Harmonia axyridis reaches a size between six and eight millimeters and becomes five to seven millimeters wide. The species is characterized by an extremely variable body color, which ranges from light yellow to dark red. The deck wings are dotted black.

Usually there are 19 points, some of which can be completely merged with one another, are weak or completely missing. In some beetles it appears as if the wing covers are colored black and spotted in red. This property earned the species the nicknames multi-colored ladybirds or harlequin ladybirds.

Pronotum:

• colored bright yellow
• black M- or W-shaped drawing
• Pattern can cover the entire pronotum

Distribution - in Europe and around the world

The natural home of this species extends across East Asia. The beetle occurs in China and colonizes southern habitats as far as Yunnan and Guangxi. Further distribution areas are in Japan, Korea and Mongolia as well as in eastern Russia. In many areas the species has been used as biological pest control since 1916, which is why the species can be found worldwide today. There seems to be a particularly high density of individuals in the vicinity of cities.

Recognize larvae

Very young larvae are initially yellow-green in color and have black bristles. Later the basic color darkens to blue-gray or black. Your body is covered with bristles. These so-called scoli have two to three branches. Noticeable are the orange colored side areas, which develop in the course of larval development express. The color 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 ladybugs

There are around 250 species of ladybirds in Europe, 82 of which are native to Germany. They colonize different habitats in which enough aphids live. This great diversity in connection with the variability in terms of body color and dot pattern makes it difficult to determine the species. The most common native species can be easily identified by a few characteristics. The color of the pronotum is important in the Asian ladybird.

Way of life and development

The Asian ladybug can live up to three years. The beetles usually reach an age between one and three months. Its development depends on environmental conditions and the availability of food. Although the beetles are often viewed as a nuisance, not all individuals survive.

pairing

Asian ladybugs mate in spring

As soon as the first rays of sun warm the earth and melt the snow in late winter, the beetles come out of their winter quarters and look for a suitable mating partner. Copulation can last anywhere from 30 minutes to 18 hours. Usually the female mates with several males, sometimes visiting up to 20 partners. Mild temperatures influence the development of the populations. Under optimal conditions, the species is able to form 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 picks out plants that are infested with aphids. The females attach their yellowish eggs to the leaves in small packages of 20 to 30 pieces. Not all eggs hatch larvae, as many fall victim to unfavorable weather conditions or hungry insectivores. After three to five days, the larvae of the remaining eggs hatch.

Larval development

The larvae take two weeks to fully develop into ladybirds. During this time, the offspring can eat up to 1,200 lice. They moult three times and then pupate directly on the leaf. The pupa rests mostly open on the upper side of the leaf. The imago hatches after another five to six days.

wintering

In their natural habitat, the beetles spend the cold season in crevices in the rock. You fall into one Numbness 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 odor causes the beetles to come together in large numbers. They keep an eye out for suitable cracks and crevices where they are safe from frost. It is not uncommon for the insects to get lost in apartments and houses. However, they do not pose a threat to the buildings.

Dangers and challenges

Despite the advantages that the Asian ladybug has over native species, it has to prove itself in nature. When conditions change, his survival advantage balances out. Scientists, on the other hand, are trying to help mankind by other means. Because it is a certain fact that the Asian ladybird can no longer be suppressed.

Enemies

One of the rare natural enemies is the forest guard. The stink bug lives predatory and hunts for insects and their larvae. They stick their powerful proboscis into the thin skins between the segments because they cannot pierce hardened chitin armor. They then suck their victim on the spot or carry them impaled to a safe place. However, the forest ranger does not manage to contain the Asian ladybird population on his own.

Climate change

The native seven-spotted ladybird has been massively displaced by its Asian relatives in recent years. When the temperatures rose, the native species was able to recover, contrary to the bad fears of conservationists. Studies have shown that domestic beetles gain significantly more weight than their Asian competitors at higher temperatures.

If the temperature rises by an average of three degrees Celsius, both species of ladybird will eat more than under normal temperature conditions. While the fat content and body mass of the seven-point ladybug increase, the development of the Asian ladybird stagnates. The species follow different strategies when it comes to energy use. The seven-point ladybird saves its energy reserves for hibernation, while the Asian ladybird invests all of its energy in the production of offspring.

As a result, there is an extreme increase in the number of Asian representatives 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 is not benefiting from climate change.

Wingless breeding

French researchers have created genetically modified variants of the Asian ladybird. These individuals do not develop wings and thus cannot spread uncontrollably. In France these cultivars are marketed as biological pest control. However, there is a risk that the specimens will cross with the wild ladybirds. The offspring can develop wings again.

Prevent spread

Ladybugs get inside through the smallest crack

The most effective means of preventing the Asian ladybug from entering the house is thorough prevention. Prevent the beetles from entering by repairing cracks and damage to the facade. Even the smallest gaps are sufficient for the insects to get into the building. Roof overhangs and supply pipes as well as windows and doors can be fitted with insect screens.

Are Ladybug Houses Effective?

Insect hotels that are specially designed for ladybugs are available in stores. They are primarily intended to provide the native species with a safe shelter for wintering. Therefore, they are equipped with warming material and are placed in a protected location.

Occasionally, the insect hotels are recommended as a shelter for the Asian ladybug. If there are large colonies on the walls of a house, a ladybug house is hardly a remedy. 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. Homeowners affected repeatedly report that camphor and menthol have a disgusting effect on adult Asian ladybird beetles. However, the duration of the effect of the secondary plant substances is short-lived, which is why the measure has to be constantly renewed.

Remove damaged fruit

The Asian ladybird changes its diet in autumn when the aphid colonies slowly perish. They then feed on sugary fruit juices. Damaged and eaten fruit from soft-skinned fruits in particular has an attractive effect on the beetles. Therefore, control your garden and remove such fruits in a timely manner.

Control in viticulture and fruit growing

A contamination of wines and fruit juices by the ladybird can no longer 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 an inventory control. If necessary, the insects can be shaken off by hand before processing the fruit.

frequently asked Questions

Is the Asian ladybug poisonous?

Although the beetle emits a bitter substance as a defense against enemies that smells unpleasant, the species does not pose any danger. It is not poisonous for dogs, cats or humans.

It can happen that the animals are crushed by the grape harvest in wine production. As a result, the bitter substances also get into the wine, where they can change the taste of the wine. This so-called ladybird tone is not harmful to health, but at most reduces the quality of the wine. Some grape varieties naturally contain the same substance that was discovered in the defense secretion of the beetle.

Can the Asian ladybug bite?

If the beetles get into a stressful situation, what is known as reflex bleeding occurs. They secrete a white to yellowish substance that is supposed to act as a deterrent. When panic, the Asian ladybug is also able to bite. However, a bite is hardly painful and completely harmless to humans.

How dangerous is the Asian ladybug for the ecosystem?

So far, researchers have not agreed on whether the invasive species can actually exterminate native ladybugs. There were always periods when the introduced beetle appeared en masse and was superior to the seven-point ladybird. Under changed environmental conditions, the populations of the Asian representative declined again in favor of the native beetles. In many places, however, the undesirable species is more common than the original beetle.

Ladybugs can be found all over the world and can assert themselves in different climates. However, they have great utility in keeping various plant pests at bay. This makes it difficult to clearly classify the Asian ladybird as a pest or beneficial insect.

How can the Asian ladybug hold its own?

The species has decisive survival advantages over native ladybirds. Researchers discovered an antibacterial substance in the hemolymph and approx. 50 different protein compounds. This allows the organism to effectively assert itself against pathogens. The Asian ladybug is less susceptible to disease than the native seven-spotted ladybug.

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 leads to death in other insects.

Where does the Asian ladybug come from?

The original home of the beetle is in East Asia. There the species was used effectively as a biological pest controller. For this reason, she was in the 20th It was shipped to America in the 18th century, where it was used in greenhouses against pests. This example was followed in Europe. However, it could not be ensured that the species would not move independently outside of the Greenhouses(€ 60.76 at Amazon *) increased.

In 2001 the first wild specimen of an Asian ladybird was found in Belgium. Since then, the species has spread en masse across Europe. This development cannot be reversed because of the lack of natural enemies.