Coccinellidae
Coccinellidae is a widespread family of small beetles. They are commonly known as ladybugs in North America and ladybirds in the United Kingdom; "lady" refers to mother Mary. Entomologists use the names ladybird beetles or lady beetles to avoid confusion with true bugs. The more than 6,000 described species have a global distribution and are found in a variety of habitats. They are oval beetles with a domed back and flat underside. Many of the species have conspicuous aposematic colours and patterns, such as red with black spots, that warn potential predators that they taste bad.
Most coccinellid species are carnivorous predators, preying on insects such as aphids and scale insects. Other species are known to consume non-animal matter, including plants and fungi. They are promiscuous breeders, reproducing in spring and summer in temperate regions and during the wet season in tropical regions. Many predatory species lay their eggs near colonies of prey, providing their larvae with a food source. Like most insects, they develop from larva to pupa to adult. Temperate species hibernate and diapause during the winter; tropical species are dormant during the dry season. Coccinellids migrate between dormancy and breeding sites.
Species that prey on agricultural pests are considered beneficial insects. Several species have been introduced outside their range as biological control agents, with varying degrees of success. Some species are pests themselves and attack agricultural crops, or can infest people's homes, particularly in winter. Invasive species like Harmonia axyridis can pose an ecological threat to native coccinellid species. Other threats to coccinellids include climate change and habitat destruction. These insects have played roles in folklore, religion and poetry, and are particularly popular in nursery rhymes.
Etymology
The name Coccinellidae, created by Pierre André Latreille in 1807, is derived from the Latin word coccineus meaning. The common English name ladybird originated in Britain where the insects became known as "Our Lady's birds". Mary was often depicted wearing a red cloak in early art, and the seven spots of the species Coccinella septempunctata were said to represent her seven joys and seven sorrows. In the United States, the name was popularly adapted to ladybug. Entomologists prefer the names ladybird beetles or lady beetles to avoid confusion with true bugs. Names in some other countries may be similar; for example, in Germany they are known as Marienkäfer meaning or.Description
Coccinellids range in size from. Adult females tend to be slightly larger than males. They are generally oval with domed backs and flattened undersides. They have large compound eyes and clubbed antennae with seven to eleven segments. The powerful mandibles typically have pairs of "teeth" which face each other. The coccinellid prothorax is broad and convex, and can cover the back of the head. Being beetles, they have hardened, non-overlapping forewings, known as elytra, which cover up the more fragile hindwings when the insects are not in flight. Their legs are relatively short, with a tarsal formula of 4-4-4. The tarsus has two claws at the tip.As adults, these beetles differ from their closest relatives with the following morphological characteristics:
- Five pairs of spiracles on the abdomen
- A tentorium with separated branches at the front and no bridge
- No line dividing the frons and clypeus
- Maxillary palps with non-needle-shaped tips,
- Divided galea and lacinia
- Smaller molar area of the mandible
- Coxal cavities that open from the back in the front of the thorax and from the front in the middle of the thorax
- Epimeron on the metathorax with parallel edges
- Lines on the second abdominal sternum
- Tube-shaped, siphon-like genitalia in the male
Coccinellid larvae are elongated with square heads. They are covered in hairs or setae, the abdominal segments, in particular, each having six divided into pairs, and one to three segmented antennae. Their colouration varies from grey, blue-grey, grey-brown or brown and spotted with white, yellow, red or orange. They tend to brighten as they get closer to adulthood.
Evolution
Fossil history
Over 6,000 living species of Coccinellidae have been described. They are sparsely preserved in the fossil record. Although molecular clock estimates have placed their origin in the Cretaceous, the oldest fossils of the group are known from the Oise amber of France, dating to the Early Eocene around 53 million years ago, which belong to the extant genera Rhyzobius and Nephus. The greatest number of fossils comes from the younger Eocene Baltic amber, including members of the extant genera Serangium and Rhyzobius as well as extinct genera belonging to the tribes Microweiseini and Sticholotidini.Phylogeny
The Coccinellidae are within the superfamily Coccinelloidea, which in turn is part of the infraorder Cucujiformia, a group containing most of the plant-eating beetles. The ladybirds form the majority of the species in the Coccinelloidea; many of the rest are fungus-feeding beetles or scavengers.Coccinellidae have historically been divided into up seven subfamilies and 35 tribes based on morphology. However, genetics studies have called into question the monophyly of most of these subfamilies. The monophyly of Coccinellinae has the most support.
A 2021 genetic study sampling many species, identified three subfamilies, Microweiseinae, Coccinellinae and a newly identified group, the Monocoryninae. All three subfamilies were strongly supported, but the study noted that although the tribes are mostly monophyletic, their relationships are only weakly supported. The study suggests that the crown group appeared some 143 Mya in the Early Cretaceous, and that the group diversified rapidly during the Late Cretaceous, perhaps because the growth in diversity of angiosperm plants then encouraged the radiation of insects of the clade Sternorrhyncha such as aphids, on which ladybirds could feed.
An earlier 2009 study concluded that consumption of scale insects is the most basal diet of Coccinellidae. Aphid-eating evolved three separate times and leaf-eating evolved twice, one of which evolved from a clade that contains both aphid-eating and pollen-eating. The fungi-eating also evolved from aphid-eating.
Biology and ecology
Flight
Coccinellids mostly fly during the day. Springy, cylindrical veins in the hindwings stiffen when in flight and bend when folding. Folding of the wings is further aided by creases in the membrane. These beetles may migrate long distances to hibernation and breeding sites, and areas with more food. They appear to be drawn to recognisable landmarks. The more crowded an area is, the more individuals leave, but will remain if there are enough prey species to feed on. "Trivial flights" refer to flying while foraging or when finding a place to lay eggs. One study of species in Britain found that coccinellids can fly as far as. They flew at speeds of and could reach altitudes close to.Life cycle
In temperate climates, coccinellids typically breed from late spring to early summer. In warmer temperate regions, reproduction may occur in spring, fall and winter; tropical species reproduce during the wet season. Mating is promiscuous. In some species, females appear to be selective in their partners, preferring males of a certain size and colour. Males produce sperm packets each with 14,000 sperm, and insert three of them into the female, even though she can only hold 18,000 sperm. This is likely a form of sperm competition. Like other insects, coccinellids develop from egg, to larva, to pupa and finally adult. Eggs tend to be bright yellow, and the females lay them close together, standing upright and near where they can access food. The number of eggs in a cluster can vary depending on the species; it is typically in the double digits but some species can lay over a thousand eggs in their lifetime.After hatching, the larvae will begin eating, including the other eggs in their clutch. Certain species lay extra infertile trophic eggs with the fertile eggs, providing a backup food source for the larvae when they hatch. The ratio of infertile to fertile eggs increases with scarcity of food at the time of egg laying. Larvae typically have four instar stages with three moults between them. The larva eventually transitions into a pupa; which involves the development of a hunch, the fusion of the legs to the body, and the attachment of the posterior to the surface.
Pupae may be uncovered, partially covered or fully covered by larval skin depending on the species. The pupa is mostly immobile, but the head can move in response to irritation. When the adult emerges, it has its hindwings, while the elytron starts out softer and lighter in colour, with no patterns. The length of each development stage varies based on climate and between species. For Adalia bipunctata, eggs hatch after four to eight days, the larva stage lasts around three weeks and the pupa lasts seven to ten days. Adult coccinellids develop much of their final colouration within hours, but may not fully darken for weeks or months. The lifespan of an adult reaches up to a year.
In temperate areas, coccinellids may hibernate or enter diapause during the winter. Individuals during this period gather in clumps, large or small depending on the species. Overwintering insects can be found both in lowland areas, aggregating under dead vegetation, and at the tops of hills, hibernating under rocks and on grass tussocks. In areas with particularly hot summers, the insects experience summer dormancy or aestivation; in the tropics, coccinellids enter dormancy during the dry season.