The common cockchafer (Melolontha melolontha), known colloquially as the Maybug, Maybeetle, or doodlebug, among many other names, is a species of scarab beetle belonging to the genus Melolontha. It is native to Europe, and it is also one of the several closely-related and morphologically similar species of Melolontha called cockchafers, alongside Melolontha hippocastani (the forest cockchafer) as the latter also shows sexual dimorphism, mating practices, and key physical features such as the number of lamellae.
The cockchafer develops via metamorphosis, in which the beetle undergoes stages of eggs, larvae, pupae and adults.
The mating behaviour is controlled by pheromones. The males usually swarm during the mating season while the females stay put and feed on leaves. When cockchafers feed, they cause leaves to release green leaf volatiles, which the males can detect and thus locate females for mating. The larvae use both the plant volatiles and CO2 to locate the plant root for food.
This species is an important and nutritious food source for many predators. The adults and larvae feed on plants, and are regarded as agricultural pests of crops such as grasses and fruit trees. Adults have harmful effects for the crop when they aggregate in large groups. The larvae can cause severe damage and kill the plant by gnawing the plant roots.
Etymology
The name cockchafercockchafer (n.) www.etymonline.com accessed 30 May 2021 derives from the late-17th-century usage of cockcock (n.1) www.etymonline.com accessed 30 May 2021 (in the sense of expressing size or vigour) + chafer which simply means an insect of this type, referring to its propensity for gnawing and damaging plants. The term chafer has its root in Old English ceafor or cefer, of Germanic origin and is related to the Dutch kever, all of which mean gnawer as it relates to the jaw.chafer (n.) www.etymonline.com accessed 30 May 2021 The term melolontha is derived from the Ancient Greek word which means cockchafer.
Taxonomic history
Melolontha melolontha was first named by Carl Linnaeus as Scarabaeus melolontha in 1758. He described it as hornless and testaceous with a hairy thorax, a bent tail, and a white abdomen. Fabricius in 1775 later named it as Melolontha vulgaris; remarking that its larvae are a root-eater, that it can be preyed on by mice, and that it can foretell autumn diseases. Moll in 1785 named the cockchafer as Scarabaeus majalis and observed that the beetles were brownish-red or multicolored.
In the 19th century, Étienne Mulsant named it as Melolontha albida and differentiated between the male and the female. In 1884, Friedrich Westhoff distinguished numerous subspecies, namely–Melolontha melolontha funesta, M. m. humeralis, M. m. luctuosa, M. m. melanopus, M. m. obscuripes, and M. m. scapularis.
In the 20th century, Georg Pfanneberg named the species Melolontha nigritarsis because the observed specimen caught in May 1903 had completely black tarsi. In 1905, Josef Petz observing a specimen caught the previous year, described a new subspecies which had a sharp deviation at the tip of its pygidium, naming it M. melolontha colpopyga. Karl Wilhelm von Dalla Torre in 1912 named a variation of the species M. redtenbacheri. In 1923, Jarosław Łomnicki found the female to have a blunt pygidium tip which varied from the one observed by Petz, and it also had an acutely posterior pronotum, and flat hairs on its pygidium. He named this M. melolontha amblypyga.
Description
Adults The adult cockchafer reaches in length. It has a dark head with two segmented antennae. Behind the head, it has a dark pronotum covered with short hairs. This black coloration distinguishes it from its close relative M.hippocastani, whose pronotum is brown. The top of its body has reddish-brown elytra and it has a black abdomen which is partly white on the sides. Male cockchafers have seven flattened leaflike extensions on their antennae, whereas females have only six. The insect's antennae are large and fan-like with the male's larger than those of the female's. Genetically, M.melolontha is historically divergent to M.hippocastani as a research study in 2024 showed that melolontha was found to have a higher genetic differentiation than hippocastani (the forest cockchafer).
Larvae M.melolontha larvae typically have three stages of development over the course of 3–4 years. In the first stage (L1), the larva is long, growing to in the second year of development (L2), and reaching in its final year of development (L3) before emerging. In some areas of Eastern Europe, the larva develops for a fourth year (L4). It has a white body, black at the abdominal extremity, which curves into a C-shaped arc, and long, hairy, well-developed legs. The larva also has a large brown head with strong, grabbing mandibles, and relies on its olfactory and contact chemosensory senses for underground foraging.
Distribution and habitat The cockchafer is prevalent across Europe, particularly in temperate regions with suitable soil conditions for larval development. It has also been reported in parts of Asia, including Turkey and the Caucasus region.Ashworth M, Darwin Tree of Life Barcoding collective, Wellcome Sanger Institute Tree of Life programme et al. The genome sequence of a cockchafer, Melolontha melolontha (Linnaeus, 1758) [version 1; peer review: 2 approved, 2 approved with reservations]. Wellcome Open Res 2023, 8:222 (https://doi.org/10.12688/wellcomeopenres.19434.1) Geographical barriers, climatic conditions, and ecological factors may limit the cockchafer's dispersal; it does not occur in the mountainous regions of Tyrol, for example, because it cannot survive at the high altitudes and low temperatures of the Alps. It also does not fly more than from where it emerges and remains in close proximity to the fields or grasslands where it occurs.
Life cycle Adults appear at the end of April or in May and live for about five to seven weeks. After about two to three weeks, the female begins laying eggs, typically in fields, which she buries at a depth of around . She may repeat this process until she has laid between 60 and 80 eggs. The preferred food for adults is oak leaves, but they will also feed on conifer needles, for example pine.
The larva, known as a "chafer grub" or "white grub", hatches four to six weeks after being laid as an egg, and feeds on plant roots such as potatoes. The grubs develop in the earth for three to four years, in colder climates even five years, and grow continually to a size of about , before they pupate in early autumn and develop into an adult cockchafer in six weeks.
During the winter season, the adult cockchafer overwinters in the earth by staying in its pupal chambers at depths usually between but it can be also found in a depth of . It works its way to the surface in spring, from April to May.
Because of its long development time as a larva, the cockchafer appears in a cycle of three or four years, the duration varying from between regions. There is a larger cycle of around 30 years superimposed, in which they occur (or rather, used to occur) in unusually high numbers (10,000s).
Behaviour and ecology
Mating Males leave the soil when temperatures become favourable in April or May. At dusk, they begin to swarm around groups of trees at forest edges, continuing until it becomes dark. The swarms typically do minimal damage to the trees, but are occasionally harmful in cherry or plum orchards because of their consumption of blossoms. The females stay in place and feed on leaves until they reach sexual maturity. Males primarily fly among the branches in search of females. Mating lasts for several hours, and males may continue seeking mates for 10–20 days. Once the females have matured and mated, they return to the fields to lay their eggs in the soil in a batch of 10 to 38 eggs. The females stay 2 to 4 days on the soil to protect the eggs. Only a third of females survive this trip, but any survivors will make a second, and occasionally third, swarming trip and return to the field to lay eggs again. The length of time for the cockchafer's eggs to mature depends on temperature—5 to 8 days at and 23 to 32 days at .
Green leaf volatiles
Green leaf volatiles (GLVs) are compounds released by plants that attract the cockchafer. They have been found to act as a sexual kairomone which helps adults to find mates. They do this by enhancing the attractiveness of toluquinone, a sex pheromone released by female scarab beetles to attract males. Only males are attracted to GLVs, in particular (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol and 1-hexanol, and they use their release to identify leaves on which females are feeding. M. melolontha males are sensitive to lower GLV concentrations than females, possibly due to the anatomical differences between their antennae. The males hover around the foliage during mating season, while females remain on twigs and branches to feed. This makes the cockchafer the first reported insect utilising both the sex pheromone and plant volatiles for mating. GLVs are being investigated as a possible pest control technique to attract males and prevent mating.
Pest
Though adults can damage some fruit trees, M.melolontha larvae are the primary agricultural pests. Larvae hatch from their eggs 4–6 weeks after being laid and develop into adults over the course of 3–4 years. Immediately after hatching, larvae will gnaw on small roots. While having only three larval stages, the larvae will continue feeding on roots, particularly grasses, cereals, and other crops, only pausing to burrow deep into the soil for winter hibernation.
In their first stage, M.melolontha larvae depend on soluble compounds such as sugar, amino acids, and isoflavonoids which are released by plant roots in rhizosphere. Hence it gets attracted by the CO2 released by respiring plant roots and soil microorganisms. Above a larval density of , the damage to soil by melolontha larvae is noticeable. In their second stage, larvae will cause the most damage to crops such as strawberry. In their third stage, larvae do less but still cause severe damage to crops. They most prominently use structures on their antennae called pore plates (or lamellae) to smell. These have a thin layer of cells over sensory units consisting of dendrite bundles. Larvae can identify CO2 and plant volatiles. They push their heads into the walls of their burrows and probe with their antennae, likely to taste the soil with bristle-like sensilla. The cockchafer larvae can also gnaw the plant roots for each day, which quickly kills the plant.
Ecological impact
Environmental factors such as prevailing soil temperature, humidity, and plant type have a considerable impact on the existence and behaviour of cockchafers in wooded environments. It indicates that cockchafer populations are strongly influenced by climatic conditions, with warmer soil temperatures and higher humidity level favouring the growth of larvae in upper soil layers and accelerate its overwintering period but a fall in humidity decreases the number of larvae with desiccation seen in them. Additionally, specific vegetation types, including deciduous trees and shrubs, provide suitable habitats for cockchafers, facilitating their survival and reproduction within forest stands.
Intestinal components and microbiome