The ladybirds (Coccinellidae) of Germany

1.   Introduction

The ladybirds (family Coccinellidae) are most probably the best known family of the beetles at all. Who does not know them, the ubiquitous seven-spot ladybird Coccinella septempunctata or the two-spot ladybird Adalia bipunctata? Every child knows the myth that the age of a ladybird corresponds with the number of spots on the elytra, and even some grown-ups take it for granted. It is generally well known, that ladybirds are useful animals, because they devour a large number of aphids during their life span. But only few people know that many ladybirds do not only prey on aphids, but also feed on mealybugs, scale insects, jumping plant lice or spider mites. Some species feed on mildew or pollen. A few species are not predaceous but phytophagous, they feed on various plants (Angiospermes) or are even regarded as pests.

2.   Morphology

The body length of the ladybirds varies between approx. 1 mm in the smallest species and roughly more than 10 mm in the largest known species. The body of most ladybirds is of short oval shape with a more or less convex surface, which makes them look rather rounded. Only the representatives of the subfamily Lithophilinae and the species of the tribes Coccidulini (Coccinellinae) and Novini (Coccinellinae) are distinguished by a markedly oblong and at the same time flattened habitus.

The antennae are mostly elongate and eleven-membered with a marked, closed club at the end. Contrary, the species of tribe Chilocorini exhibit short, eight- to nine-membered antennae, but the club is well marked too.

Fig. 2: (a) without pubescence, Halyzia sedecimguttata; (b) with pubescence, Platynaspis luteorubra

The apical member of the maxillary palps is typically ace-shaped. There are species without noticeable pubescence (especially the well-known species from subfamily Coccinellinae, e.g. Coccinella septempunctata or Adalia bipunctata), but also species with a very dense pubescence of the upper body surface (e.g. genus Scymnus, Rhyzobius and others). The legs are of normal shape and the tarsi are four-membered. The second member of the tarsus is lobate, the third is very small and inconspicuous in most cases and is more or less "hidden" between the lobes of the second. In a superficial examination the tarsi appear to be three-membered (hence the tarsi are also described as "pseudo-trimeric" or "cryptotetrameric").

On the lower side of the body five to six sternites are conceivable; morphologically, the first visible sternite is in fact the third sternite. Virtually all species are macropterous, that means they have well developed wings and are able to fly. Only a few species, like Spiladelpha barovskii (native to Russia), are apterous, that means they do not have wings and are uncapable of flying. In the Central European species Rhyzobius litura only around 7% of the beetles have developed wings, hence this species can be regarded as mostly flightless.

3.   Coloration

The variability of the ladybirds is immense. The primary base colors are yellow, red, black and brown. Not only the pattern, but also the coloration itself can vary considerably in a species, causing beetles of the same species to look so different, that a layperson might believe in two distinct species. For example, more than 150 aberrations have been described of the two-spot ladybird (Adalia bipunctata). Although they are scientifically meaningless, they still give an impression of the tremendous variability of this species regarding both color and pattern. Other species like the ten-spotted ladybird (Adalia decempunctata) and the Harlequin ladybird (Harmonia axyridis) don't fall short of the two-spot ladybird in any way regarding their variability.

Fig. 3: Color variations of the Harlequin ladybird Harmonia axyridis

Fig. 4: Color development in ladybirds: (a) Sospita vigintiguttata; (b) Adalia bipunctata; 1=immature, 2=fully colored; Photos © Ingrid Altmann, use with written permission.

In some species however, among them the seven-spot ladybird (Coccinella septempunctata) the coloration is relatively constant which makes them easier to determine. Despite the same pattern, the size of the spots can still vary considerably (in the seven-spot ladybird especially in the east of its distribution range), which makes the differentiation from the very similar Coccinella magnifica more delicate.

The light colors are based on derivatives of carotenoids, whereas the black color is caused by the pigment melanin. After hatching from the pupa, the beetles requires a few days for cuticle tanning (i.e. to reach full color and sclerotization of the exoskeleton). Many ladybirds might be recognized a few minutes after hatching by the base color, but some still lack the black color pattern, like the seven-spot ladybird. Initially its base color is orange and turns into the typical deep red within a few hours. This process is also called ontogeny of the color pattern. Sospita vigintiguttata is special in this respect: Freshly hatched animals exhibit a light-brown base color, which remains intact throughout the summer and autumn. Only during hibernation they develop their typical black color pattern, a sign for a longsome maturation process.

4.   Distribution

The family of the ladybirds comprises approx. 6000 species worldwide, thereof 82 are (or were) recorded from Germany. Ladybirds are present in nearly all parts and habitats of the world with exception of regions of eternal ice and water. Apart from the latter two ladybirds are present in all habitats where plants provide the livelihood for aphids, scale insects and other prey. The range of many domestic species in Germany reaches for beyond the German borders into the North and South, as well as to the East.

Fig. 5: Number of ladybird species by terrestrial ecozones

The seven-spot ladybird is known to occur throughout Europe and reaches East Asia and the Japanese archipelago. Other species are restricted to the European continent, e.g. Myzia oblongoguttata, Scymnus nigrinus or Aphidecta obliterata. Particularly thermophilousous species hardly reach our territory. Clitostethus arcuatus for example is a species of southern distribution, which profits from the current global warming by expanding its range slowly towards the north.

Fig. 6: Number of ladybird species imported to Europe in the years 1875 to 2008 by origin (after H. Roy, A. Migeon, BioRisk 4(1): 293–313 (2010))

Even more extreme is the occurrence of Scymnus subvillosus in Germany, which has been recorded from very few warm locations – entirely isolated from the its normal range: The species is known from a few locations in Baden, Palatinate, Rhineland, Brandenburg and Saxony, whereas the nearest occurrences are located in the far southeast of Europe, in South Slovakia. Such cases are referred to as extinction zone within the distribution range of a species. Other species can only survive above a certain elevation in the mountains, e.g. Hippodamia alpina which is limited in Germany to the Alps and the alpine range of the Black Forest in Baden-Württemberg. In some cases the habitat is the limiting factor: Brumus oblongus and Oenopia impustulata are only present in moors and bogs. These species are called "boreal"; they can only exist in these locations due to the local cool climate of these habitats. Many German species however are present throughout the country. Their presence is normally only limited by the availability of their food resources (aphids etc.), which are ubiquitous in most cases.

Occasionally alien species are recorded which are not part of the Germany or even European fauna at all. These beetles have been either introduced with transports or have been actively imported as a biocontrol agent against pests in greenhouse horticulture. One of these examples is the Australian mealybug ladybird Cryptolaemus montrouzieri, which is used as a biocontrol agent against mealybugs in greenhouses and tropical displays in botanic gardens. As this species is very sensitive towards cold temperatures, escapees cannot survive even the mildest winters in Central Europe and consequently cannot establish populations in the wild.

More widely known is the Harlequin ladybird Harmonia axyridis, which was introduced with transports to Western Europe, but was also actively imported as a biocontrol agent against aphids in greenhouse horticulture. Originating from Japan and East Asia this species is capable to survive the Central European winter. Within a few years the species has spread across entire Germany and has arrived in Eastern Europe. Also the British Isles and South Europe have recorded established populations of the Harlequin ladybird. Despite initial fears that the voracious beetles and their larvae might be detrimental to our domestic ladybird fauna, observations in regions where Harmonia axyridis has been present for a while are different: While the domestic species initially suffered population losses, they have meanwhile reached back to population sizes within the normal range. Meanwhile Harmonia axyridis is also attacked and decimated by various parasites and parasitoids. The populations have already swung into or will shortly swing into a "natural" equilibrium.

5.   Hibernation

Fig. 8: Harmonia axyridis landing and preparing for hibernation in Bammental, Germany. Photos © Jutta Bastian, use with written permission.

Hibernation is a fascinating aspect in the life of the ladybirds. Some species tend to aggregate for hibernation. All species displaying this type of behaviour have two things in common: They feed on prey animals (mainly aphids) with a limited period of occurrence, and they have long dormancy periods. Aggregators select rather different locations for hibernation aggregation, and two basic schemes are distinguished: On the one hand the so called hypsotactic, on the other hand climatotactic aggregators.

If the beetles use terrestrial cues for orientation to potential dormancy sites, i.e. structures protruding from the surrounding environment (building, trees or hills) this behaviour is called hypsotaxis. In contrast, climatotactic aggregation is determined by physical factors, like humidity, wind flow and temperature. Aggregations can range from the gathering of a few animals under leaves (e.g. in Halyzia sedecimguttata), over aggregations of several hundred animals under bark or in roller shutter housings (often observed for Oenopia conglobata, Coccinella septempunctata and Adalia bipunctata) up to several hundred thousand or even millions of animals in crevices.

The invasive species Harmonia axyridis shows a remarkable form of aggregation. In their regions of origin they hibernate preferably in crevices. As described above, the beetles use optical cues to find the crevices, which are often of a different color than the surrounding environment. In Europe, the beetles fly to window frames, light-coloured walls and rotting trees by mistake. The first beetles arriving at the potential dormancy site secrete a pheromone, whih attracts further Harlequin ladybirds. In this way the aggregation becomes gradually bigger until the beetles start to hide in cracks and crevices at windows, under roof tiles or similar spots. Often such mass aggregations can be found in roller shutter housings. Beetles suddenly appearing inside houses or apartments normally arise from aggregations at windows, which warm up after the start of the heating period, causing the beetles to wake up from their dormancy. If these beetles cannot find cool spots within a short period of time and continue their dormancy, they quickly deplete their energy reserves and starve to death.

At least in Europe dormancy is only known for adult ladybirds. Only in very rare cases larvae have been found in winter dormancy, and no eggs or pupae so far at all.

6.   Development

Fig. 9: Development stages of Calvia quatuor­decim­guttata: (a) adults mating; (b) oviposition; (c) egg clutch; (d) freshly hatched larvae; (e) larva; (f) pupa. Photos © Ingrid Altmann, use with written permission.

Normally ladybirds mate shortly after the dormancy period. Although mostly several copulations take place, one is typically enough to fertilize a female permanently. The semen is stored in the so called receptaculum seminis, where it stays useable for the entire lifespan of the female. The number of eggs per deposition varies considerably in the European species. It has been elucidated for around one third of the domestic species and ranges between 2 in Stethorus punctillum and 51 eggs in Coccinella septempunctata. The duration of the egg development largely depends from temperature. Under outdoor conditions it takes five to ten days.Towards the end of the egg development the unhatched larva can be seen through the transparent egg menbrane. The larvae of most species have so called egg teeth on the upper side of the prothorax and the head to break to egg membrane open. The entire hatching process can take around one hour or more. The egg teeth are lost after the first molt – first instar larvae are therefore easily recognizeable by the presence of egg teeth.

In ladybirds always several eggs ripe simultaneously, therefore the deposition takes place on portions. Females of the tribes Coccidulini and Scymnini deposit their elongate eggs single and laying. Cracks in bark, leaf folds and axils are preferred. Only a few Chilocorinae deposit their eggs in the vicinity or even directly at their prey. The females of Epilachninae and Coccinellidae however deposit their eggs in small clutches. The eggs are attached by their blunt end to the substrate and the resulting clutches are relatively regular. The number of eggs in such clutches varies normally between 20 and 40, but can go up to 60 eggs. The deposition takes place on the upper or lower side of leaves and needles, occasionally on bark, but in almost all cases near their prey. Hence freshly hatched larvae can start feeding on their prey immediately after hatching.

The larvae of the ladybirds are variable regarding both shape and color, but many share a common basic scheme, which allows also laypersons with limited knowledge to recognize many ladybird larvae easily. The habitus is elongate, with the greatest width behind the head and continuously narrowing towards the apex of the abdomen. The segments of the body are clearly separated and equipped with bristles or spines or at least colored to mimic it. The legs are strong cursorial legs, which allows the active search and pursuit of prey. The larvae of Scymninae – with exception of tribe Stethorini – are covered with a waxy substancewhich can make up to 25% of the body volume depending on the respective species. These larvae resemble mealy bugs themselves. The purpose of this waxy layer is unclear: It might serve as protection against predators, as the UV reflections makes it impossible for them to distinguish between the scale insects and the larvae. It is established however, that it does not protect the larvae against parasites.

The larvae of Epilachninae are characterized by branched bristles on their back, the so called scoli. They cannot be mistaken with any other ladybird subfamily in Central Europe although the larve of the tribe Chilocorini exhibit similar bristles, however far less branched. The latter case is not a sign for a phylogenetic relationship, but rather a independent development.

The larvae of the subfamily Coccinellinae are of the most widely knows type and are most probably plainly reecognized as ladybird larvae. The base color is grey or blueish grey to brown or yellow in case of Psyllobora. The spots are black in Psyllobora, and yellow, orange or red in other species of the subfamily. Contrary to the adult beetles in the subfamily, the coloration and pattern of the larvae is very constant and allows a determination to species level. The only exception are the larvae of Adalia bipunctata. Their color pattern varies from entirely darf specimen without any spots to specimen wir up to seven distinct spots.

The larva of Platynaspis luteorubra differs from this general type: The larvae are of broad build and flattened. From dorsal view they are egg-shaped with a row of three fine bristles at the edge of each segment. Similarly, the larvae of the genus Hyperapis differ from the general type of Coccinellidae larvae: From dorsal view they are of oval shape, although not as marked as the larvae of Platynaspis luteorubra.

Normally, the ladybird species have four larval instars. A few species have an additional fifth instar. The size of the larvae varies between 1.5 mm (Stethorus punctillum) an up to 15 mm (Anatis ocellata). Naturally the size data are somewhat ambiguous, as the size varies depending on the nutritional status of the larva in each instar. The duration of the larval development takes – depending on temperature, available feed/prey and further factors – three to six weeks.

Pupation takes plase on leaves, branches, bark or other plant parts. Contrary to most other beetle species, the pupa of Coccinellidae is a so called pupa obtecta (similar to the chrysalis of lepidopterans) in which the appendages are closely bound to the body. The pupa is normally attached to a surface an lies free. No cocoon or puparium are formed. In Epilachninae, Noviini and Chilocorini pupation takes places in the skin of the last larval instar. It just slightly bursts at the back and offers a glimpse of the pupa. The pupation of Scymnini and Hyperaspini takes place similarly, however the skin bursts open so that the front half of the pupa lies free. The pupal period takes ten to 14 days under outdoor conditions.

7.   Parasites

Like many other animals ladybirds are attacked by a number of predators, parasites and parasitoids. Despite the fact that the eggs of many other insect species are parasitized by hymenopterans of various families (z.B. Mymaridae and Encyrtidae), and despite tremendous research efforts this kind of egg parasitism could not be observed in any carnivorous European ladybird species. In principle, the eggs a large enough in at least in some phythophagous ladybirds eggs are regularly parasitized. One reason for the missing of egg parasites could be the fact that parasites normally slow down the development and hatching of the host. As carnivorous ladybird larvae feed on the remaining eggs and egg shells this would be a risk for the parasite. However, there might be different reasons for the absence of egg parasites.

Fig. 10: The scuttle fly Phalacrotophora bruesiana. Photo Brian Brown.

Contrary to the eggs, larvae are regularly parasitized. Hymenopterans of genus Homalotylus are known parasites. Also hyperparasitism has been observed: Occasionally the Homalotylus larva is parasitized itself by other hymenopterans. Further known parasites of ladybird larvae are the hymenopterans Pachyneuron muscarum (probably as hyperparasite), Oomyzus sempronius and Tetrastichus epilachnae. Normally, an infestation is not easily visible, as the parasites attack the vital organs at a late stage in the development thus killing the host.

Ladybird pupae are parasitized as well. Hymenopterans like Oomyzus scaposus, Aprostocetus neglectus, Metastenus concinnus and the dipterans Phalacrotophora berolinensis and Phalacrotophora fasciata (family Phoridae) are known as examples. In these cases several individuals of the parasites hatch from the parasitized pupa.

But not only larvae and pupa are attacked. Also adult beetles are attacked by entomoparasites. Noteworthy is the braconid wasp parasite Dinocampus coccinellae. Probably it deposits its eggs already in the pupa or larva. In the first larval instar the parasites have sharp mandibles. The parasite larvae start killing each other until only one larva is left. This larva hibernates jointly with the beetle. In early spring it leaves the beetle and pupates in a cocoon attached to the leg of the living ladybird, whose brightly colored body and occasional twitching reduce predation. The paralyzed ladybirds, twitching, and attached to the cocoon have been compared to zombies. Interestingly, around 25% of the ladybirds recover after the cocoon has been emptied. Recent research suggests that Dinocampus transmits an RNA virus, which causes the paralysis of the ladybird⁸.

Fig. 12: The tachinid Medina separata. Photo © Patrick Derennes, use with written permission.

The tachinid fly Medina separata (Diptera, family Tachinidae) has developed a special method of infesting it host. It perches itself on the back of the beetle. If the perturbed beetle opens its elytra slightly Medina separata uses this short moment to place an egg underneath the elytra. The larva hatching from the egg burrows its way through the intersegmental membrane into the abdomen of the ladybird. The second larval instar hibernates within the beetle and concludes its development cycle only in the spring of the following year once the beetle has started to feed. The developed larva leaves the host and pupates in the ground. The females of Medina separata seem to attack only female ladybirds. It is unclear, if and what kind of advantage this behaviour brings for the larva.

Further probionts and parasites of ladybirds are mites, which use the ladybird as "taxi" or live as parasites on the lower side of the beetle and feed on hemolymph of the beetle without killing its host. In the intestines and in the abdominal cavity live Aschelminthes of various genera. The infestation with Aschelminthes does not seem to be fatal for the beetle, but stops oogenesis.

Many parasites and parasitoids are not particularly selective when choosing a host. Normally they parasitize the species of an entire or even several, closely related subfamilies. Metastenus concinnus only attacks pupae of species of the tribe Scymnini. In contrast Aprostocetus neglectus attacks representatives of the subfamily Coccinellinae as well as Scymnini and Chilocorini. Phalacrotophora berolinensis has been observed as parasite of Anatis ocellata and Adalia bipunctata. The female of Phalacrotophora berolinensis deposits its eggs on larvae close to pupation. Seemingly the egg deposition does not hinder the larva to normal pupation. However, a few days after pupation the parasites hatch within the pupa. After concluding their development they leave their host and pupate in the ground.

Fig. 13: Harmonia axyridis infected by a obligate insect ectoparasitic fungus (Laboulbeniales). Photo © Juliane Ahlers, use with written permission.

There is also a number of predators which hunt ladybirds. Besides spiders (Araneae) also ground beetles (family Carabidae) attack ladybirds, also hoverfly larvae (family Syrphidae), green lacewing larvae (Chrysopidae) and shield bugs (Pentatomidae) prey on ladybirds. Despite the warning coloration (aposematism) and the so called "Reflex bleeding" (beetles exude alkaloid-containing lymph through the joints of the exoskeleton) there is a number of vertebrates that prey on ladybirds. Eurasian Tree Sparrows (Passer montanus) collect large numbers of coccinellids to feed their squabs. Further predators include shrews, lizards and frogs as revealed by examinations of stomach contents. Ladybirds also tend to cannibalism, which is an additional threat to the eggs and larvae.

Finally, ladybirds are also not untroubled by diseases. There is a number of viruses, bacteria and fungi, microsporidia and gregarines that infest and kill ladybirds.

8.   Fact sheets

Thanks

To make this page was possible thanks to the support of a number of people. The following persons contributed photographs of beetles and larvae: Ingrid Altmann, Jutta Bastian, Brian Brown, Fred Chevaillot, Patrick Derennes, Josef Dvořák, Eric LeRoy, Rudolf Macek, Heidi Röder and Lynette Schimming. Their support is gratefully acknowledged. We further thank Irina Würtele and Ingrid Altmann for the review of the draft and helpful comments and suggestions.

Literature

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