Harmonia axyridis (Pallas, 1773)
In recent years this ladybird has come to be considered as one of the world’s most invasive insect species. Its success in this respect is due to a combination of factors; it is tolerant of a wide range of climatic conditions and will thrive in almost any habitat with sufficient food, its ability to utilize a wide range of prey species including other ladybirds, both as adults and larvae and in this respect it has the advantage of being larger than several other common species, it is highly resistant to some diseases that can kill other ladybirds, and it carries a microsporidian parasite to which it is immune but can kill other species. Their natural defence or alarm response is to ‘reflex bleed’ producing a very pungent yellow liquid which leaves a bright stain, and this gives them some protection against humans, and some people are even allergic to this, as well as other potential predators e.g. larger insects or birds. Beyond this they are voracious insectivores and naturally aggressive and so as they spread into new areas there is generally a corresponding decline in native species, a phenomenon that has been seen to drastic effect in the United States and Europe in recent years. The harlequin is also becoming a pest in the wider sense, mostly in houses where they may overwinter in numbers but also among soft fruit crops where they bite the ripening fruit; the taste of wine is very badly affected when grapes so damaged are used. This generally common native East Asian species is now widespread in many areas of the world, partly due to accidental introduction through trade etc. but also from deliberate introductions as a biological control agent in greenhouses and among a wide range of arable crops to help deal with aphids and scale insects. Many such ‘invasions’ are of a recent origin e.g. the first deliberate introduction to the United States was in 1916 but this failed to establish, as did several subsequent attempts, and the first ‘wild’ population was found in 1988 in New Orleans and this, along with a more eastern population, has since spread to include most of the United States and southern Canada. It has also spread through much of the Neotropical region e.g. Brazil and Argentina, and is widespread in South Africa; both of these populations are thought to be independent of the Nearctic one. The recent use of genetic markers has revealed the origins of some populations e.g. in Europe the species originated mostly from North America but with significant input, about 40%, from individuals introduced as biological control agents.
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Adults become active when the temperature exceeds 10°C and so in temperate regions this is usually from March or April, after overwintering, although occasional individuals will be seen during the winter as a result of local solar heating or from temperature fluctuations when they overwinter in houses etc. The adults fly readily and so are very mobile, occurring almost anywhere; in hot weather they seem to be common in any town centre on walls, windows or pavements etc. or on the trunks of trees, and often in numbers either spread over a wide area or in tight aggregations. Oviposition occurs throughout the spring and summer when eggs are laid in small batches, generally 10-30, among foliage or on stems where there are populations of aphids etc. and over her lifetime a female will produce between 1000 and 2000 eggs. The newly hatched larvae will consume at least part of the chorion before wandering off to predate other insects, they will consume aphids, scale insects, thrips and lepidopteran eggs and larvae as well as, drastically, the eggs, larvae and adults of other ladybirds, they can move quickly and are agile and so can out-compete other species for food. The adults are primarily insectivorous but will also feed on developing or ripe fruit; in the United States they have occurred in swarms in vineyards and are increasingly being considered a serious pest. Eggs hatch within four or five days and the larvae pass through four instars; the entire cycle, from oviposition to adult, may take only four or five weeks depending on temperature and food supply. The pupal stage lasts for about a week. In the U.K. oviposition generally begins in May with the majority of eggs laid during June and July, pupae appear from July and new generation adults in late July and August. In Europe and Asia there are typically two or three generations each year, sometimes overlapping, and in warmer climates there may be four or five or they may breed continuously. In the U.K. there may be a partial second generation in late summer with the adults overwintering and breeding in the spring or mating in the autumn and storing the sperm to fertilize the eggs which are laid in the spring. Unlike some other ladybirds which need a period of winter dormancy before they can breed, and so produce only a single generation, the harlequin can apparently breed at any time.
The large size, 5-8mm, and general habitus are distinctive; strongly convex with broad and angled shoulders which are wider than the pronotum, and elytra which are explanate at least in the basal half and have a transverse fold before the apex. The head is smooth and either black towards the base and pale anteriorly or completely black but for a triangular pale mark on the frons. The antennae are a little narrower than the width across the eyes. The pronotum is either black with pale margins or with four or five black spots, which may be merged, forming an M against a pale background. The elytral colouration varies widely and more than 100 forms have been named, these are best appreciated by looking at pictures online; there are many descriptions written but most attempt to classify the various forms discreetly and after a while it begins to seem pointless, some occur in differing regional frequencies and even the NBN maps three forms, and many more occur outside the U.K. An appreciation of several of the more distinctive forms is all that is needed to identify the species in any of its variations. The most common forms in the U.K. seem to be orange with 15-21 dark spots, or black with two to four orange or red spots of varying size. The appendages are reddish-brown and generally paler in lighter coloured specimens, and the ventral margins of the abdomen are widely and distinctly brown, even in melanic forms. The meso-epimera are white, the met-epimera pale yellowish-brown and the episterna black. The Prosternal process has two parallel longitudinal carinae and the anterior margin of the mesosternum is weakly excised. In males the prosternum is pale while in females it is dark. The femoral lines on the first ventrite are weak and bifurcate, reaching the hind margin but not the anterior margin. The tibiae lack spines and the claws have a strong basal tooth.