For nearly a hundred years the multi-colored Asian lady beetle, Harmonia axyridis has been used as a biological control agent. They are native to Asia from the Altai Mountains in the west to the Pacific coast in the east, and from southern Siberia in the north to southern China in the south. The first reported release of H. axyridis in the United States as a biological control species was in California in 1916. It wasn’t until 1988 that they were considered established within North America. There is speculation as to whether this establishment was from intentional release or from accidental occurrences. Many attempts to release this species as a biological control occurred after 1916 and each attempt seemed to have failed. With the discovery of an established population in 1988 the population of this species has spread exponentially. They now occur throughout most of the United States with exception to parts of the Southwest, Idaho, Montana and Wyoming.
(Map taken from Bugguide.net)
The multi-colored Asian lady beetle is listed in the family Coccinellidae with other lady beetles. This species went through many name changes beginning as far back as 1773 when it was originally known as Coccinella axyridis. It wasn’t until 1915 that the name H. axyridis was finally decided on by Jacobson, and is still used today. There are nearly 475 species of Coccinellidae in North America, and we can now add H. axyridis to this number as it is now considered an established species.
Likely the polymorphism of this species is inherited, each type passing on its own color to its offspring. Diet, temperature and other environmental influences may also contribute to color variations. No other species of lady beetle exhibits this type of polymorphism. This highly variable appearance can make identification difficult; therefore it may be necessary to use other key identification factors when identifying this species. In this species the characteristic to look for is a distinct “M” shape on the pronotum. Sometimes this mark may look more like two lines, or a series of four black spots. This species of lady beetles has more white on its pronotum than any other lady beetle species. All this variance in appearance has earned this species numerous common names including Halloween beetle, Harlequin ladybird, Japanese ladybug, Asian lady beetle, pumpkin ladybird, and the many-named ladybird.
The larval stage of this species goes through four distinct stages; egg, larval, pupae and adult. The larvae must go through four to five instars to reach adult size. There may be up to five generations per year depending upon region and temperature.
This species occasionally participates in cannibalism during the larval stage. Predominantly it is the eggs that are preyed upon by the larva. In large aggregations of aphid populations where H. axyridis eggs are laid the larvae of non-siblings feed on large amounts of eggs. In areas where aphid populations are reduced feeding on eggs or larvae provides necessary nutrients. However they seem to recognize fellow siblings and are most likely to feed on non-siblings. This practice affects overall population growth in a given area. It may affect populations as much as 16 percent in a given area.
Another factor affecting population growth is a bacterium in the genus Spiroplasma. This bacterium targets the male eggs which reduces the risk of cannibalism of females by siblings. The consumption of nonviable male eggs reduces the risk of starvation of female offspring by infected females. This behavior is so far not reported in North America, but instead is restricted to their native Asian range.
H. axyridis have a keen ability to track down aphid populations which is the main reason they are favored as biological control. The mating season of H. axyridis corresponds with peak aphid population growth. They must time oviposits with high densities of aphid populations in order to provide enough food sources for their offspring. Low populations of aphids would cause starvation of their offspring. There are indications that sight plays a huge role in larvae locating aphids. Larvae of H. axyridis will climb stems in search of aphids. Studies show that they hunt more frequently during daylight hours rather than nighttime. Females are able to detect aphids by smell from short distances which aid her in finding appropriate food sources for her offspring. Multi-colored Asian lady beetle larvae are voracious eaters and may consume up to 370 aphids during this stage. In their lifetime they may consume up to 4,000 aphids.
Even with their aposematic (warning) coloration and reflex bleeding of alkaloid secretions they still have enemies. Certain species of flies will lay their eggs within H. axyridis as will a parasitic braconid wasp called Dinocampus. These parasitic predators lay their eggs within the lady beetle. The resulting offspring will hatch and feed on the lady beetle from the inside. Once the wasp or fly larvae have reached full size they will pupate. Shortly thereafter the beetle will die. There are also numerous birds that will feed on these beetles as well as certain species of ants. Other lady beetles will also feed on H. axyridis but only if they are smaller. Spiders have also been reported to feed on H. axyridis when they are unfortunate to become ensnared in webs.
The introduction of H. axyridis to the United States was to provide biological control of aphid populations in a wide variety of crops. The first crops designated for release were pecan groves and red pines. Despite the intentional release into the environment during the early to mid-century it wasn’t until the late 1980s and early 1990s that establishment was realized. They not only controlled aphids in pecans and red pines, they also moved to other areas and exhibited successful control of aphids in a wide variety of crops. These crops include apples, soybeans, citrus, sweet corn, hops, strawberries, peaches, cotton, alfalfa, winter wheat, and tobacco as well as many others.
For many years insect supply houses provided H. axyridis for purchase, but fewer supply houses are rearing them now because of the invasive implications now associated with this species. In the larval stage they are an effective control of aphids as well as scale insects in pine groves, this effectiveness comes from their inability to fly at this stage. The effectiveness of this species was questioned in the adult stage because of their ability to fly to other regions. In order to improve control in this species a flightless strain was created and released. This flightless specimen proved effective because of its inability to fly.
Pesticides used to control insect pest populations have little adverse affects on H. axyridis except in the larval stage. Synthetic pyrethroids seem to affect H. axyridis less than it does aphids. The adult beetles are less affected by pesticides, fungicides and other chemicals in the environment than are the larvae. With constant changes being made in the pesticide industry and safer chemicals being developed all the time fewer H. axyridis are falling victim to chemical applications.
While it is true that H. axyridis is excellent at aphid control, as well as the control of other soft-bodied insects like thrips and scale insects, we must ask ourselves, at what cost? They are not particular about their diet and feed on a wide variety of insect prey including other lady beetle larvae. This can cause a serious decline in native species of coccinellids, and may potentially lead to several species being listed as imperiled. Nine-spotted lady beetles, Coccinella novemnotata are becoming increasingly more difficult to find in their native range. It is suspected that the much larger and more aggressive H. axyridis is at the very least partially responsible for this decline. In addition to native species falling prey to H. axyridis, they are also less able to compete for viable food sources against a much larger and voracious hunter. The result is less food to sustain the population of native species. Monarch butterfly eggs and young caterpillars have even fell victim to H. axyridis.
There is no question that H. axyridis is more than capable of providing excellent aphid control, but the cost may be considered too high. They not only feed on nuisance insects, they also feed on beneficial insects as well as insects that hold a worldwide appeal such as butterflies. In addition, as with most exotic biological control species that become too abundant, they cause problems for humans. In the fall they form large aggregations on human dwellings, and other structures. This leads to many of these insects finding their way inside homes. It is not uncommon for these beetles to form aggregation populations in the hundreds of thousands. Persons sensitive to their presence have on occasion developed an allergic rhinoconjunctivitis as well as other allergies. As they fly around our homes and land on surfaces they leave behind frass which can trigger allergic responses in individuals that are sensitive, especially if they occur in large numbers. Many people find it annoying to have these lady beetles accumulate inside their homes and fight an ongoing battle each fall to control their numbers. The secretions of these beetles stain furniture, floors and curtains. Many homeowners use toxic chemicals to kill the lady beetles, others are more tolerant and remove the lady beetles by vacuuming them up and moving them back outside. This species is reported to give off a musky odor when disturbed and may inflict a minor bite. Not only is it homes that face invasion, so do beehives. Beekeepers reportedly fight to keep these lady beetles out of hive boxes. They appear to cause no harm to the bees themselves, but are a nuisance to the beekeeper.
H. axyridis is one of just a few species of lady beetles that form large aggregations in the fall. In their native range of Asia they are known to orient themselves to visual landmarks on the horizon. Often these areas are mountains or large rocky hillsides. They will use these sights to hide within cracks and crevices to wait out winter’s icy blast. In the United States they incorporate this same orientating technique and often “home” in on our houses and other structures. There are reports of these beetles making their way into hospital operating rooms and into institutes with bio-containment facilities. These are areas with zero tolerance policies in place for possible biological invasion of outside pests. They have also been reported to contaminate food processing plants, making their way into food being processed for human consumption. This destroys large lots of food costing significant financial losses to those companies. It is believed they are more widely attracted to buildings at higher elevations. They are also reported to aggregate on mountain ranges such as the Smoky Mountains. They are also attracted to light colored structures, such as white, tan, yellow, etc. However, this does not mean they won’t be found on other buildings as well.
These beetles will hibernate, or enter into a type of diapause beginning about November and ending in March. They are not looking for places to stay warm, as most places where they spend the winter months are not heated. They instead are waiting for winter to end and warm weather to return so their food source will once again be plentiful. They seek areas that protect them from exposure to the outside weather. I’ve found them in basement window wells, behind the bark of trees, and under rocks. H.axyridis use pheromone cues to signal to others of their kind that a suitable location has been found. It is these chemical cues that lead to such large numbers of lady beetles accumulating in a given area. They may also smell feces left behind by previous aggregations of Harmonias indicating that the location is suitable. They prefer areas that are cool with little to no light. Basements or attics are perfect overwintering areas for these beetles. Occasionally during the winter we have a warming of weather, on these days H. axyridis will become active and seek out warmth. It is not uncommon to find them flying into light fixtures or towards windows. This warming of temperatures seems to trigger a chemical response in the beetle that signals them to wake up and become active again. As soon as the temperature drops again however they will once again become dormant. The biggest problem comes in the autumn and spring when the beetles are moving in or out of structures. It is at this time that human contact is the highest and most aggravating.
Besides using harsh insecticides to keep these lady beetles out of our homes, the use of DEET and camphor have been used successfully as a deterrent and are much safer alternatives. The beetles find these odors offensive and will avoid areas that are sprayed with these chemicals. One drawback to using DEET is its ability to dissolve paint. Therefore it must be applied to surfaces that will not suffer from its application. There are DEET strips that can be purchased and used and would be a less expensive way to repel these beetles. 4 While the large aggregation of these beetles is no doubt annoying and bothersome, killing them outright may not be the best solution depending upon your viewpoint. If you are a gardener or farmer you may appreciate the biological control of aphids they provide, even if you temporarily forget their importance when trying to keep them out of your home. On the other hand if you prefer native species of lady beetles and are opposed to the much more aggressive newcomer displacing our own lady beetles you may feel differently and have no love for these beetles.
H. axyridis sets itself apart as one of the few lady beetles that will feed on substances other than aphids and soft bodied insects. They will also form aggregations in fruit orchards and gather on the ripening fruit. It has been reported they will feed on apples, pears and grapes thus ruining the fruit meant for human consumption. Vineyards suffer the highest economic impact of the H. axyridis. The beetles are next to impossible to remove from the grape clusters, so many are crushed along with the grapes. The result of this insect contamination is tainted wine with a foul flavor that cannot be consumed. All of these negative impacts of the beetle can cause significant economical losses to fruit growers, homeowners and consumers. More research needs to be done to quantify the annual financial impacts this species is causing to the environment, orchards, and croplands.
Ongoing research is being done to further understand the potential impact H. axyridis will have on all native species of coccinellids. Cornell University is a driving force in the research being done on this species. They currently have a citizen science project underway that involves persons from North America. They request that people head outside and photograph lady beetles. Submit your photos, along with data to their website and all information is processed to better understand the impact that H. axyridis is having on the environment. Their website www.lostladybug.org is instrumental in raising awareness of the plight of native lady beetles, and in providing information on H. axyridis.
Exactly why they were imported into the United States for release, beyond the obvious aphid control, is unclear. Apparently persons in the agricultural industry felt the need for a more aggressive aphid predator than our native species. Many attempts to introduce this species into nut groves, pine groves, orchards, croplands and other areas of commerce failed. This continuation of failures did not stop efforts to try and establish this species. One has to wonder if at any time was it seriously questioned the appropriateness of continuing with further releases. It wasn’t until the late 1980’s that an established population was discovered. From this original colony the spread of this species ran rampant. Currently it is found throughout most of North America in large numbers. In Missouri where I live it is the most commonly seen lady beetle. The only other species I find on a regular basis are the convergent lady beetle (Hippodamia convergens) and the pink-spotted lady beetle (Coleomegilla maculate), and their numbers are much lower than in years past. Over the course of a personal 6 year study I’ve found a significant decrease in native species and a large increase in H. axyridis.
In conclusion this species should be considered neither beneficial nor harmful. They provide excellent control of harmful insects such as aphids and scale insects. Their large numbers gives them an advantage in the consumption of large numbers of these harmful insects. On the flip side their prolific breeding and large populations are potentially causing the demise of our own native species of lady beetles. The formation of large aggregations can be an annoyance to humans and potentially cause health problems. Their association with orchards and other fruit crops can lead to destruction of food. To say the good outweighs the bad, or vice versa, would be difficult without further research. I believe it will take time to discover the final verdict on this species.
1 1.) Role of Visual Contrast in the Alighting Behavior of Harmonia axyridis
(Coleoptera: Coccinellidae) at Overwintering Sites
C. A. NALEPA,1 G. G. KENNEDY,2 AND C. BROWNIE3
2.) The multicolored Asian lady beetle, Harmonia axyridis: A review of its biology, uses in biological control, and non-target impacts R L Koch
2.) The multicolored Asian lady beetle, Harmonia axyridis: A review of its biology, uses in biological control, and non-target impacts R L Koch
3.) The multicolored Asian lady beetle, Harmonia axyridis: A review of its biology, uses in biological control, and non-target impacts R L Koch
4.) www.bugguide.net (http://www.europe-aliens.org/speciesFactsheet.do?speciesId=50711)5.) http://www.europe-aliens.org/speciesFactsheet.do?speciesId=50711