Harmonia axyridis, the multi-colored Asian beetle, also known as “Halloween beetle”, “Japanese beetle” or “harlequin ladybird”, is a species of beetle native to Asia, belonging to the Coccinellidae family.
Its native range is presumed to extend from the Altai massif in western Asia, to the Pacific coasts in the east, and from southern Siberia in the north to southern China. This insect was imported by the United States Department of Agriculture in 1916 and later in 1964 and 1965, with the purpose of controlling aphids and other pests.
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However, the first populations were found in 1979 and 1980 in Louisiana; consecutively in the year 1994, ladybug populations were observed in Alabama, Georgia, South Carolina and Florida. Today, populations of the beetle can be found in North and South America, Europe and Asia.
For decades, H. axyridis has been used as a biocontrolling agent, especially of different species of phytopathogenic aphids such as Aphis spiraecola and A. glycines. It also contributes to the control of the aphid Rhopalosiphum maidis and the lepidopteran Ostrinia nubilalis, important pests in sugarcane and corn crops.
At the same time, it has been documented as an excellent pest biocontroller in soybean, cotton, alfalfa, tobacco, citrus and wheat crops. Unfortunately, the lack of dietary specificity coupled with their high dispersal capacity can lead to unintended adverse ecological effects through the predation and displacement of beneficial native insects.
Similarly, H. axyridis has become a potential pest in the processing and production of fruits, especially wine grapes. During harvest, the beetle infested clusters are accidentally crushed, causing the release of alkaloids that give the resulting wine an unpleasant taste and smell.
On the other hand, domestic insect infestations are not only a nuisance to the owner. Some people tend to develop H. axyridis allergic rhinoconjunctivitis; others, on the contrary, have reported cases of stings and infestations in hives, resulting in a nuisance for the beekeeper, but at the same time they are not harmful to bees.
As a consequence of the detrimental effects reported, the multicolored Asian beetle has been included in the Spanish Catalog of Invasive Exotic Species. Therefore, it is necessary to implement pest management programs that range from the use of light traps, chemical pesticides, biological insecticides, to the use of parasitic insects and natural enemies for population control.
characteristics
The adult beetles are 4.9-8.2 mm long and 4.0-6.6 wide; oval and slightly convex body. In relation to its pigmentation, this species presents polymorphism in coloration, that is, both the coloration and the pattern of its spots will be influenced by diet and environmental temperature; although there may also be variations depending on the season of the year.
Its head can be black, yellow or black with yellow spots. The elytra, or hardened wings, have different color patterns, ranging from pale yellow to orange with black dots or completely black elytra with red dots. The spots or spots on the abdomen of the insect may be absent or present, and if this is the case the number amounts to 19 spots.
The shape of the egg is oval, moderately flattened, with a length of 1.2 mm. After laying, its color changes from pale yellow to dark yellow and, 24 hours before hatching, the color of the egg changes to a dark grayish.
The larval stage consists of four instars; the larva is 1.9-2.1 mm long in the first instar, while in the fourth instar it reaches a length of 7.5-10.7 mm. Its shape is slightly flattened, covered with small tubercles and thorns.
During each phase, the larvae undergo changes in the pigmentation of the abdominal segments. As in other members of the Coccinellinae subfamily, the pupae are exposed and the exuvia or molt of the fourth instar remains attached to the posterior end, in order to facilitate the adhesion of the pupa to the substrate.
Lifecycle
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Like the members of the Coccinelidae family, the multicolored Asian beetle is a holometabolo insect, that is, it has four morphologically distinct life stages: egg, larva, pupa and adult.
After laying eggs in early spring, at an approximate temperature of 26⁰C, the egg hatches after 3 days. Subsequently, the first instar lasts 2.5 days, the second instar 1.5 days, the third instar 1.8 days and the fourth 4.4 days.
During each change, the larva undergoes a shedding of skin according to the change in size. At the end of the fourth instar, the larva pupates and in this state of inactivity it lasts approximately 4.5 days. After a few days, the adult emerges from the pupa.
Development time from egg to adult requires 15 to 25 days, depending on the environmental temperature and the availability of food. Usually an adult lives between one to three months, but records have been found of adults who can live up to three years.
Habitat
Its great dispersal capacity makes the multicolored Asian beetle a cosmopolitan species, found widely in the United States of America and Canada. In Europe, the species H. axyridis can be found in the Czech Republic, Denmark, France, Germany, Greece, Holland, Italy, Latvia, Lithuania, Luxembourg, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Spain, Sweden, Switzerland, Ukraine, Ireland, England, Austria, Belarus and Belgium. It has also been reported in Argentina, Egypt, and Asia and part of South Africa.
Reproduction
During her entire lifespan, the female can produce from 1,642 to 3,819 eggs, about 25 eggs per day. Although it has been described as a bivoltine species (two generations per year) in its place of origin, in Europe between four to five generations are observed during the year.
In the first generation, after adult hibernation, all females are reproductive; in the second generation, a few females enter diapause (a state of physiological inactivity); In the third and possibly fourth generation, most females enter diapause.
Feeding
The species H. axyridis is a voracious predator of numerous species of insects. During its larval stage, the beetle can consume between 90 to 370 aphids, approximately 23.3 per day, depending on the species of aphids it consumes.
On the other hand, an adult of H. axyridis can consume between 15 to 65 aphids per day, with the females that feed on a greater number of insects compared to the males. Color and smell generally play a role in predation as well.
In addition to aphids, its diet can include mites (Tetranichidae), hemiptera (Psyllidae), mealybugs or also known as scale insects (Coccoidea), immature stages of coleopterans (Chrysomelidae), weevils and weevils (Curculionidae), as well as than larvae of moths and butterflies (Lepidoptera).
Likewise, it tends to feed on pollen from flowers and on fruits such as apples, cherries, pears, and grapes. In some cases, where food and nutrients are scarce, cannibalism tends to be observed, mainly of instar IV larvae.
Biologic control
The H. axyridis species has become a pest capable of reducing populations of native and beneficial insects; as well as constitutes a threat in the production of the fruit and a sanitary danger. For this reason, methods for the management and control of population densities have been implemented.
Physical or mechanical control involves the use of light traps, including black light traps, effective for capturing adult beetles confined to dark and isolated locations. Traps can reduce up to 50-70% of the population.
Also, domestic infestations can be prevented by sealing entry points such as cracks, windows, holes or vents. Currently, pheromone traps and semi-chemical baits are being investigated.
The effectiveness of the chemical control will depend on the stage of development. Larvae are more susceptible compared to adults, however, most insecticides used in the field are toxic to the species, especially Fenpropatrin, Carbaryl, Chlorpyrifos and λ-cyhalothrin.
On the other hand, natural enemies can be used in different ways to control invasive insects such as H. axyridis. The organisms used as biological controllers range from pathogenic organisms, predators, parasitoids, nematodes and parasitic mites.
Pathogens
There are numerous studies that focus on the use of entomopathogenic fungi (fungi that attack insects) in coccinellids. The spores of the Beauveria bassiana fungus significantly reduce egg production; yet adults are usually resistant to infection.
On the other hand, the ectoparasitic fungus Hesperomyces virescens has been found infecting different members of coccinellids, including H. axyridis. This fungus is usually located in the ventroposterior area of males and in females, in the dorsoposterior part.
The infection spreads directly through copulation, causing a decrease of 22-38% of the population in winter and, in spring, mortality rises to 62%.
Predators
Parasitic diptera belonging to the tachyinid group have been found parasitizing adults of H. axyridis; among them we find the members of the species Strongygaster triangulifera and Medina (= Degeeria) luctuosa (Diptera: Tachinidae).
Parasitism shortens the life of the host and prevents the development of eggs. The wasp Dinocampus coccinellae (Hymenoptera: Braconidae), is a common ectoparasite in certain populations of coccinellids in Europe, Asia and North America; Despite this, only populations of H. axyridis from Asia are shown to be susceptible to parasitism compared to populations from Europe.
Another parasitoid insect found in the literature is the species of phalacrotophora philaxyridis (Diptera: Phoridae), capable of parasitizing the pupa.
Nematodes
- Kenis, M., H. Roy, R. Zendel & M. Majerus. Current and potential management strategies againts Harmonia axyridis. BioControl. 2007 Oct. DOI: 10.1007 / s10526-007-9136-7
- Robinson, W (2005) Urban insects and arachnids. Cambridge. New York, United States: 3-456
- Jervis, M (2005). Insects as Natural Enemies: A practical perspective. Springer. Holland, Netherlands. 1-723.
- Koch, R. The multicolored Asian lady beetle, Harmonia axyridis: A review of its biology, uses in biological control, and non-target impacts. Journal of Insect Science. 2003 Oct. 32 (3): 1-16.
- Ecology of Harmonia axyridis. Global invasive species database. Available at: issg.org