Coccinella septempunctata, commonly known as the seven-spot ladybird (in North America, seven-spotted ladybug, seven-spotted lady beetle), often abbreviated C-7, is a carnivorous beetle native to Europe, most of Asia, and North Africa. It inhabits many regions with a temperate climate. The beetle has been introduced to several other areas, including North America as a biological pest control agent to combat aphid infestations. It is one of approximately 5,000 species of ladybird worldwide. Tatia Bauer states that C. septempunctata ability to adapt to many different habitats makes it "one of the most successful aphidophagous insects".
C. septempunctata was first described and named in 1758 by the Swedish biologist Carl Linnaeus. Coccinella, the name of the genus, comes from the Latin for the colour "scarlet". The common name is reflected in the Latin name for the species, meaning "seven" and meaning "spotted".
C. septempunctata elytra is red in colour, with three black spots on each wing. A further spot appears where the two wings join, giving a total of seven black spots. Their principal diet is aphids, on which they also depend for development and reproduction. When aphids are scarce, seven-spot ladybirds will survive on alternative food sources such as pollen, nectar, thrips and whitefly, but they cannot reproduce during that time. Predators of C. septempunctata include birds, small mammals, spiders, and other Coccinellidae.
Description The adult Coccinella septempunctata has an oval, convex shape. It has a body length of and a width of about , with orange-red elytra (forewings) and seven black spots on the elytra. There is one black spot next to the beetle's scutellum where the two elytra meet. There are also two white patches on the elytra just ahead of this black spot. The remaining six black spots are distributed across the elytra, three on each. The size and position of these six spots on the elytra may vary between individuals. Spot fusions and melanic forms are rare. Additionally, C. septempunctata has two white spots on the front of the pronotum on each side of the inner edge of its eyes. The underside of the beetle's abdomen, the pronotum, and the legs are black.
Sexual dimorphism exists in C. septempunctata, although the differences are subtle and microscopic. The shape of the seventh abdominal segment (sternite) is different in males and females. Males have four types of setae on their front legs that are used for traction, whereas females only have three. Females have a greater mass and are slightly broader than males. Males have an average of 18 chemosensory (sensory receptor) basiconic sensilla on their labial palps, while females have only 16. Examining the appearance of the seventh sternite has been found to be a reliable method of determining the sex of C. septempunctata specimens.
Larval instars C. septempunctata eggs are long, orange or yellow in colour, and spindle shaped. The newly hatched larva of the first instar is long, but increases to about after four instars. They are highly segmented and can vary in colour depending on the temperature, although they are generally dull black with a pale brown line along the dorsal side of the abdomen. The tubercules and hairs are sparse and small. The relatively long legs lighten towards the end. The fourth instar is dark grey to black with black tubercles emitting fine hairs. On the first and fourth abdominal segments, the dorso- and ventro-lateral tubercles are orange, and the meso- and metathorax are a pale grey.
Pupae are about long, and the colour usually varies from grey to black, but can often be pale orange with dark triangle-shaped marks across the middle, with four dark spots on the anterior surface. The black pigment in the pupa decreases as the temperature changes during its development. The pupa's hard exoskeleton develops during the fourth instar, and is roughly the same size as a full-grown seven-spot ladybird.
Reproduction and lifecycle Coccinella septempunctata has a four-stage life cycle: egg to four larval instars, to pupa, to adult. The cycle time from egg through to adult ladybird is about six weeks. C. septempunctata can breed up to five generations per year.
The breeding season begins towards the end of spring, and reproduction occurs through copulation. Ladybirds start breeding as soon as they reach sexual maturity, which occurs ten to fourteen days after they emerge as adults. Courtship is initiated by male ladybirds, but immature females or females ready to lay eggs will resist a male's advances. Females release volatile sex pheromones ("calling behaviour") to attract males. Females that have recently mated are less likely to call than unmated females, and the presence of other ladybirds does not appear to influence calling frequency. The seven-spot ladybird breeding is polygynandrous; female ladybirds mating with multiple males increases fecundity, the viability of the eggs, and the percentage of successful offspring.
In summer, female C. septempunctata with fertilized eggs will start laying them in clusters of about ten to thirty, on leaves, stems and other vegetation. Using olfactory signals, they avoid laying them in areas that already have C. septempunctata eggs. This species often produces more eggs than the environment can support, which increases offspring mortality, but this is beneficial when aphid populations are high. On average, female ladybirds lay between 250 and 500 eggs in their lifetime.
C. septempunctata larvae hatch from the eggs after about four days, although this timeframe depends on ambient temperatures. This species has four progressively larger instars, the length of which is influenced by temperature and the availability of aphids. The larvae begin by eating their own eggshells, and then any infertile eggs nearby. When the fourth instar is ready to pupate, it stops feeding for a day and attaches its abdomen to the substrate. The C. septempunctata pupal stage lasts for about eight days, after which the ladybird emerges with soft elytra and no pigmentation. The black and red colours of the beetle's elytra develop from melanins, and the lighter colours evolve from carotenes.
C. septempunctata do not provide any parental care for their young. The role of male ladybirds is purely to impregnate females, while the role of female ladybirds is only to produce eggs and deposit them on safe substrates with sufficient food for the larvae. Adult C. septempunctata have a lifespan of about one to two years, which is dependent on whether they survive through the winter.
Behavior and ecology Coccinella septempunctata has motility and can fly. It is active during the day and dormant at night. During hibernation, seven-spot ladybird adults gather in clusters for warmth and protection, and to ensure that when they exit diapause, they will already have potential mates for breeding. When preparing to hibernate, C. septempunctata emit a pheromone to attract other ladybirds to their overwintering site. This particular chemical cue has been identified as 2-isopropyl-3-methoxy-pyrazine. C. septempunctata also detects chemical cues to locate prey. Aphids release a pheromone to warn other aphids of predators, and some plants release particular chemicals when they are infested with aphids. Seven-spot ladybirds are attracted to both types of cues.
Diet
The adult and larval stages of Coccinella septempunctata feed on aphids, which are essential for their own development and reproduction. They consume at least twenty-four different species of aphid. Some aphid species, such as the lupin aphid (Macrosiphum albifrons), are harmful to seven-spot ladybirds. M. albifrons feed largely on alkaloid-rich lupin plants, and absorb compounds from the host plant that are toxic to some coccinellid species. Gruppe and Roemer stated that these aphids "have a narcotizing effect when eaten by C. septempunctata". Christy Finlayson et al. stated that studies showed that M. albifrons consumed by C. septempunctata interfere with the ladybird's development. C. septempunctata generally avoids M. albifrons, particularly in areas where the seven-spot ladybird has been introduced and not previously exposed to these aphids. Coccinellids native to those areas, for example Coccinella trifasciata, have evolved to tolerate the toxic compounds; they consume M. albifrons without competing with introduced species for prey.
C. septempunctata is carnivorous and polyphagous, although not as broadly polyphagous as other ladybug species like Harmonia axyridis and Coleomegilla maculata, which can successfully develop and reproduce on a diet of non-aphid food. Aphid populations are seasonal, and peak in spring and early summer. When aphids become scarce, C. septempunctata will switch to alternative sources of food, on which they can survive, but not reproduce. Alternate food sources include nectar, pollen, whitefly and thrips. C. septempunctata larvae will also feed on other coccinellidae larvae if there is a shortage of aphids. Some adult seven-spot ladybirds will even resort to eating conspecific eggs and larvae. Bauer states that "Intraguild predation and cannibalism are major pressures in this species and family."
C. septempunctata is generally euryphagous in its ability to eat alternative sources of food. In preparation for overwintering, and when aphid populations have declined, seven-spot ladybirds feed on the pollen of flowering plants in the Compositae and Umbelliferae families, as well as on fungal spores, in order to build up energy reserves in the form of body fat to survive the winter. When C. septempunctata emerge from diapause in response to rising temperatures, they feed on the nectar of flowering plants such as Prunus spinosa.
Some species of ants are beneficial to C. septempunctata because they farm aphids. Aphids secrete a sugary honeydew from the terminations of their alimentary canals, which the ants feed on. Ants will also "milk" aphids by stroking them with their antennae. During the winter months, ants gather and store aphid eggs in their nests. In spring, when the aphid eggs have hatched, the ants carry the young aphids to plants where they suck sap from them and secrete honeydew.
Predators and parasites Known predators of Coccinella septempunctata are birds, small mammals, spiders and other Coccinellidae. Other insects, such as lacewings, will feed on ladybird eggs. C. septempunctata fourth larval instar is particularly vulnerable to predation, and many larvae are lost during this stage. But adult C. septempunctata have few enemies in nature due to effective anti-predator adaptations. Their distinctive high contrast black and orange spots and conspicuous colours deter potential predators. The species also has a defense mechanism called reflex bleeding, whereby it emits a foul-tasting alkaloid fluid from its leg joints. When threatened, a ladybird sometimes secretes the foul-tasting substance for protection. The toxic alkaloids that C. septempunctata synthesizes are N-oxide coccinelline and the alkaloid's free base, precoccinelline. The colour of the seven-spot ladybird's elytra and its spots size are an indicator of how toxic it is to predators. The diet and sex of the seven-spot ladybird do not influence the spot size.