Coccinella septempunctata or seven-point ladybird is a species of coccinellid, native to Europe, Asia and North Africa. Due to its potential as a pest biocontroller, there have been several deliberate introductions to the United States between 1956 and 1971, primarily for the control of the aphid Aphis gossypii.
Since it was established in North America, the ladybug has been found hundreds and thousands of miles from its original site of establishment. In the United States, C. septempunctata has been reported to compete with and displace several native species of other members of coccinellids, causing population declines.
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The ladybug has been widely used to control aphids in greenhouses and often appears as a natural enemy of aphids on citrus, bean, sunflower, potato, sweet corn, alfalfa, wheat, sorghum and walnut crops. It has also played an important role as a pollinator for the endemic and endangered plant Disanthus cercidifolius.
However, C. septempunctata is a highly competitive species, capable of predating and displacing other native coccinellids. In addition, cases of bites have been reported during ladybug invasions in Great Britain, as well as damage to cultivation and processing of wine grapes.
In its adult stage, C. septempunctata has few natural enemies since it has a particular defense system - toxic compounds that exude from the gland between the femur and the tibia - and are highly harmful to common predators such as birds and small mammals.. Fortunately, it is prone to infections caused by entomatogenic fungi, wasp attacks, and protozoa.
characteristics
Adult beetles are relatively large, 7-8mm, with a pale patch on both sides of the scutellum (posterior part of the mesonotum). This species also has two characteristic pale spots along the anterior side of the pronotum.
Its body is oval and has a domed shape. Pigmentation develops over time and the red color deepens in the next few weeks or months after emerging from the pupa.
The number of dots can vary between 0 and 9, although typically adults are red with seven black dots. The red and black pigments in the elytra are derived from melanins, while the lighter areas develop from the carotenes. At a temperature of 25⁰C, the average longevity is 94.9 days.
The egg shape is oval and elongated (1mm long), and they are vertically attached to the leaves and stems. Eggs take approximately 4 days to hatch, although increasing the ambient temperature reduces or prolongs the duration of the egg stage.
The larvae remain in the eggs for 1 day after hatching. The shells, neighboring larvae and infertile eggs are eaten. During this stage, four instars or stages can be observed, one different from the other in terms of size.
Depending on the availability of food, the larvae grow between 1mm to 4-7mm in length in a period of 10-30 days.
Before pupating, the fourth instar larvae do not feed for at least 24 hours. The tip of the abdomen is attached to the substrate of the plant. It is partially immobile and stooped as it can raise and lower the front region in response to perceived danger.
The coloration may vary depending on the ambient temperature; at high temperatures the pupa exhibits an orange coloration and at low temperatures, the color ranges from dark brown to black.
Habitat and distribution
The seven-point ladybug is a generalist species, and can be found in most habitats where aphids are present. This includes herbaceous plants, shrubs, and trees in open fields, grasslands, swamps, agricultural fields, suburban gardens, and parks.
In Britain it is usually found in a wide range of plants, including: nettles, thistles, willows, brambles, Scots pine, wheat, barley, beans, sugar beets and peas.
During the winter, the adults will form groups of about 10 to 15 individuals (although more than 200 individuals have also been recorded), within the densely packed foliage of low-lying grasses.
To attract individuals, they implement chemical signals not only for the aggregation of individuals during the winter, but also ensure that the group will come out of diapause with a local population with whom it will later bond. That way it guarantees its reproduction.
It has also been found under rocks in the tundra and in the field of rocky mountains, at altitudes that exceed 3,000 meters above sea level. Its distribution covers all of Europe in temperate zones, parts of Asia and North Africa, Canada and the United States. The state of Montana and Washington are believed to be the westernmost records in the United States.
Reproduction
Ladybugs have the ability to lay more than 1,000 eggs each during their lifespan, about 23 eggs a day, for about three months beginning in spring or early summer.
The average age of sexual or productive maturity of females is from 11 days and that of males is 9 days.
The eggs tend to be deposited in small groups protected from the sun on leaves and stems near the aphids. The species C. septempunctata reduces oviposition when its prey is scarce, resuming it when food availability is abundant. Also, there is a tendency to vary the size of the cluster and the quantity of the egg produced, but it does not reduce its size.
Another characteristic in the reproductive biology of the species is that it requires diapause before the start of reproduction.
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Like all coccinellids, the seven-point ladybug lacks parental care, that is, neither the female nor the male takes care of it beyond providing nutrients to the eggs and depositing them in safe and resource-rich places.
Feeding
The spores penetrate the skin of the insect and the hyphae (cells of the fungi) grow at the expense of the insect hemolymph. Once dead, the hyphae of the fungus break the skin internally and cover the body of its host with spores, a process known as "mummification".
The microsporidia of Nosema hippodamia and N. coccinellae (Protozoa) significantly reduce the longevity of the beetles. The vertical (mother to child) and horizontal (between different species) transmission of spores can be highly efficient. Studies have reported 100% horizontal transmission of an unidentified microsporidium in Hippodamia convergens eggs predated by C. septempunctata larvae.
Parasitic wasps of the family Eulophidae and Braconidae, and flies of the family Phoridae parasitize larvae of C. septempunctata. The braconid wasp Perilitus coccinellae and Coccinellae dinocampus are the species best known as parasitoids of the species.
P. cocellae develops in synchrony with the larvae and adults of its host, it can even remain in a type of induced diapause (physiological inactivity) until the ladybug also leaves the diapause.
The C. dinocampus wasp lays its eggs inside the abdomen of its host's female, and as the egg hatches, the larva feeds on the ladybug's eggs. The pupa of the parasitic wasp develops within a leg of the host, and 9 days later emerges as an adult. Some adult beetles can relive this event and continue their cycle normally, however most die.
Bibliographic references
- Invasive Species Compendium. Coccinella septempunctata (seven-spot ladybird). Taken from cabi.org
- Shelton, A. Coccinella septempunctata (Coleoptera: Coccinellidae). Biological control a guide to natural enemies in north america. Cornell University. Taken from biocontrol.entomology.cornell
- Bauer, T. University of Michigan- Museum of zoology. Coccinella septempunctata sevenpotted lady beetle. Taken from animaldiversity.org
- Riddick, E., T. Cottrell & K. Kidd. Natural enemies of the Coccinellidae: Parasites, pathogens, and parasitoids. BioControl. 2009 51: 306-312