Harlequin ladybeetle
Harmonia axyridis
Profile
The Asian ladybug is a voracious aphid predator that has been used for biological pest control. In the field, it has spread enormously rapidly and has become an invasive species that poses a threat to native ladybugs and beneficial insects as a food competitor and predator. In addition, it can cause damage in viticulture and orchards.
Appearance
Beetle: The adult Asian ladybug reaches a length of 6-8 mm and is thus significantly larger than most European ladybug species (<5 mm).
Basically, three color variations of the mating wings can be distinguished:
- The basic coloration of the mating wings varies from mustard-yellow to orange to red with no spots or up to 21 black spots
- Black ground coloration with 2 orange-red dots
- Black ground coloration with 4 orange-red dots
Very often there is a black marking on the neck shield, which is "M" or "W" shaped depending on how you look at it. The lines of this marking may be connected or interrupted. Other individuals (often those with a black wing ground color) do not have this marking, but have a large black spot in the center of the neck shield. A distinct characteristic of the Asian lady beetle is a slight elevation in the posterior portion of the upper wings.
Larvae: The older larvae are very conspicuous: on the back they carry branched appendages that give them a spiny appearance. The appendages from the first to the fifth abdominal segment are orange, providing a striking contrast to the blackish-gray body. The last larval stage can reach a size of 1 cm.
Risk of confusion
There is a danger of confusion especially with the two-spotted lady beetle(Adalia bipunctata), which may have similar black markings on its neck shield.
Some native ladybug species are similar in size to the Asian ladybug:
- Seven-spotted ladybug(Coccinella septempunctata): 5.5-8 mm.
- Eye spot ladybug(Anatis ocellata): 6-9 mm
- Seven-spot ladybird(Coccinella magnifica): 6-8 mm
- Four-spotted ladybug(Harmonia quadripunctata): 5-7.5 mm
- Stripedladybug (Myzia oblongoguttata): 6-8 mm
- Ceratomegilla undecimnotata: 5-7 mm
Due to the variable coloration of the Asian ladybug, there is therefore a risk of confusion with native ladybugs.
Biology
The adult Asian ladybugs appear from the end of March/April. After mating, the females lay their eggs in clusters on plants infested with aphids. The beetle develops from the egg through four larval stages and the pupal stage to the adult beetle.
Larvae are found primarily in June and early October. One larva eats between 90 and 370 aphids during its development period of about two weeks (Hukusima and Kamei, 1970).
In October/November, they set out in search of suitable winter quarters.
Host plants
Viticulture
When aphid colonies are no longer present in the fall, the Asian lady beetle seeks out other food sources. Since grapes have a high sugar content in the fall, they are readily accepted as food. The beetle is attracted to grapes that are already damaged, but there are also reports that it feeds on undamaged grapes. Grape varieties that tend to burst open and very late ripening varieties such as Cabernet Sauvignon, Cabernet Franc, or Riesling are particularly at risk and affected.
Fruit growing
In fruit growing, ladybugs are very useful in spring and summer, as they effectively destroy aphids. In the fall, the Asian lady beetle can feed on various pome and stone fruit varieties as well as berries. Affected are apple, pear, raspberry, blackberry, currant, apricot, peach, plum, mirabelle and cherry; on peach and raspberry he eats even if they are not yet pre-damaged.
Distribution
Originally, the Asian ladybug originated in eastern Asia (China, Japan, Korea, Mongolia and southern Russia).
The aphid hunter was bred for natural pest control and successfully used mainly in glasshouse crops, first (1916) in the USA, and from 1995 onwards also in some European countries (e.g.: France, Belgium and the Netherlands). In the meantime, however, it has been established in the field in much of the USA, in Europe and South America, and in some African countries. In Austria, the first report of Asian lady beetle accumulation was in the fall of 2006 (Rabitsch and Schuh, 2006). In the meantime, reports on the occurrence of the beetle are available from all federal provinces.
Propagation and transmission
Unlike most ladybug species native to northern Europe, the Asian ladybug is capable of forming several generations a year, depending on the prevailing temperatures: in the UK there are two, in Greece four, and in Asia even five generations. Due to the formation of several generations in a year, there is a rapid increase in population. This favors rapid dispersal.
Economic importance
The Asian ladybug was originally used for biological control of e.g. aphids in glasshouse crops, its spread into the field was not actually intended. It is an invasive species that has spread enormously rapidly and poses a threat to the biodiversity of native ladybug species: as a direct food competitor and as a predator with a broad food spectrum that also eats the eggs and larvae of other beneficial insects. For overwintering, the beetles form large aggregations and invade houses, where they are a nuisance. In addition, Harmonia axyridis can cause damage to orchards and vineyards.
Prevention and control
- Control measures in viticulture and orcharding
- Since the wine defect of a "Harmonia wine" can no longer be completely reversed, but at best alleviated by the addition of oak chips or activated charcoal, it is particularly important to prevent such contamination from the outset (Pickering et al. 2006b). The risk of economic damage depends on the population density of the Asian lady beetle. Control measures should be based on pest density and damage threshold.
- Since grapes/fruits are usually infested just before harvest/harvest, Asian lady beetle infestation levels should be checked two weeks prior, e.g., by means of boniture or glued yellow boards.
- Mechanical
- Damaged grapes and fruit should be removed to avoid attracting the Asian lady beetle in the first place. It is important to make sure that no beetles get into the harvest or crop. In smaller plants, beetles can be shaken off the grapes/fruit by hand if necessary. In the case of mechanical harvesting, there is a risk that the beetles lodged in the injured grapes/fruit will get into the mash.
- Plant protection products
- No pesticides are currently registered for Asian lady beetle control.
- Research is being conducted on other control measures such as repellents and attractants. Camphor and menthol have a deterrent effect on adult Asian lady beetles, but these plant secondary ingredients have a very short duration of action.
Fachinformation
Weinbau
Der eigentliche Schaden entsteht durch die Geschmacksbeeinträchtigung des Weins durch den Abschreckstoff des Marienkäfers. Bei Bedrohung entlassen sie ein abschreckendes Sekret („Reflexbluten“), welches Pyrazine (2-isopropyl-3-methoxypyrazin, 2-sec-butyl-3-methoxypyrazin) enthält, die einen erdigen bis ranzigen Geruch aufweisen. Die Käfer fressen sich in die Trauben hinein, wo sie schwierig zu entfernen sind. Werden die Käfer mit den Weintrauben verarbeitet, wird das Aroma durch die Pyrazine verdorben und führt zu einem unerwünschten, bitteren Geschmack (Weinfehler).
Versuche in den USA und der Schweiz haben gezeigt, dass bereits 1 bis 1,9 Asiatische Marienkäfer pro kg Trauben die geruchliche und geschmackliche Qualität von Weißweinen (Testsorten: Chasselas, Riesling) mindern. Bei roten Rebsorten (Testsorten: Blauburgunder, Frontenac) waren erst bei fünf Käfern pro Kilogramm Qualitätseinbußen festzustellen. Basierend auf diesen Ergebnissen wurde in den USA eine Schadensschwelle hinsichtlich einer Geschmacksbeeinträchtigung von 1 Asiatischen Marienkäfer pro Traube festgelegt (Galvan et al., 2007a).
Zur Abschätzung der Befallsstärke durch den Asiatischen Marienkäfer im Weinbau wird in den USA folgende Methoden empfohlen: bei 25 Trauben wird der Anteil an befallenen Trauben über einem Schwellenwert von 1 Asiatischen Marienkäfer pro Traube bewertet (Galvan et al. 2007a). Sind 10 % der untersuchten Trauben mit mindestens einem Asiatischen Marienkäfer infiziert, ist mit Geschmackseinbußen zu rechnen (Schwellenwert bei Riesling).
Obstbau
Vereinzelt gibt es erste Berichte aus Österreich, dass der Asiatische Marienkäfer im Obstbau Qualitätsschäden verursacht. Im Gegensatz zum Weinbau sind für den Obstbau bislang noch keine wirtschaftlichen Schadschwellen festgelegt worden. Aufgrund der zahlreichen Obstsorten und deren unterschiedliche Reifezeiten ist es im Obstbau auch weitaus schwieriger konkrete Angaben über den Zeitpunkt einer möglichen Schädigung durch den Asiatischen Marienkäfer zu machen. Grundsätzlich sollte ebenso wie im Weinbau kurz vor der Ernte (zwei Wochen) ein Monitoring gemacht werden.
Vor allem bei der Vermarktung von frischen Beeren/Tafeltrauben und Verarbeitungsprodukten wie z.B. Obstsäften kann es zu Qualitätsverlusten kommen. Werden die Käfer mit den Früchten geerntet und verarbeitet kommt es ähnlich wie beim Wein zur geschmacklichen unumkehrbaren Beeinträchtigung.
Bei Problemen mit dem Asiatischen Marienkäfer im Obst- und Weinbau wird ersucht unsere Expertinnen und Experten zu kontaktieren.
Die Bestimmung von Harmonia axyridis kann von uns am Institut für Nachhaltige Pflanzenproduktion durchgeführt werden.
Last updated: 07.09.2023
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