Beetle (Coleoptera): Classification, General Morphology, and, Life Cycle
The insect order Coleoptera is known as the Beetle family. The Greek words for “sheathe” and “wing,” respectively, are keleos and pteron, which translate to “sheathed wing” and “coleoptera,” respectively. The front pair of wings, known as the “elytra,” of most beetles, which have two pairs in total, are hardened and thickened to serve as a protective sheath or shell for the rear pair and the back portion of the beetle’s body. Almost 25% of all known life forms are members of the order Coleoptera, which has the most species of any other order. There are over 400,000 species of beetles, which make up about 40% of all described insect species, and more are continuously being discovered. A hundred million species, both known and unknown, have been estimated to exist overall. Beetles are found in a very wide variety. Except for the ocean and the polar regions, they can be found in all major habitats. Some species can adapt to almost any type of diet. The largest family of insects, the Scarabaeidae, has more than 30000 different species worldwide. The Beetle can be viewed as a pest because many of these plants are crucial for forestry, agriculture, and domestic use. Beetles are not only a nuisance, but they can also be helpful by reducing insect numbers. The ladybug or ladybird is one of the best and most well-known examples (family Coccinellidae). On aphid colonies, the larvae and adults are observed feeding. Other ladybugs consume mealybugs and scale insects as food. They may eat other things like tiny caterpillars, juvenile plant bugs, honeydew, and nectar if their usual food supplies are lacking. Predators of several insects and other arthropods, such as fly eggs, caterpillars, wireworms, and others, include ground beetles (family Carabidae). Pestilent flies and parasitic worms that breed in bovine manure have been successfully controlled by dung beetles (Coleoptera, Scarabaeidae). Dung beetles are a crucial part of the terrestrial ecology both taxonomically and functionally.
The largest order of insects belongs to the class Coleoptera. There are over 350,000 species in 115 groups that are currently known to exist there, but according to recent estimates, there may be hundreds of thousands or perhaps millions of undiscovered species. Beetles are tremendously diverse in terms of size, form, and ecological tactics in addition to being extremely rich in species (Lawrence and Britton, 1991; Balke et al., 2002).
Classification of Beetles
Order: Coleoptera (Beetles)
The four suborders of Beetles are called Adephaga, Archostemata, Myxophaga, and Polyphaga (Charles et al., 2005).
Nearly all natural environments, or vegetative foliage, including trees and their bark, flowers, leaves, and underground near roots, as well as inside plants like galls and tissue from dead or decomposing ones, are home to coleoptera. The larval and adult stages of about 3/4 of beetle species are phytophagous, meaning they live in or on plants, wood, fungi, and a range of goods that are kept in storage, such as cereals, tobacco, and dried fruits.
There are three main sections to a beetle: the Head, Thorax, and Abdomen
The Head is a capsule, which is primitively prognathous and hypognathous, with the mouthparts facing forward. The head may be divided into fairly well-defined areas, with the horn of heads there are short till to longhorn, usually, heads are the location of antennae, mouth part, and eye. The front is that part of the upper surface lying between the eyes and is limited anteriorly by the clypeus, which is typically separated from the frons by a frontoclypeal. The compound eyes are widely variable in size and may be absent or so large that they meet above and/or below the head, as is the case with the family Dermestidae, which has medium-sized ocelli but only two ocelli on average. the variable antenna Small in size as larvae, some species’ antennae have 11–12 segments, while others have 8–10 segments or, maybe, 30 segments that are longer than the group’s bodies. Aside from some species of male beetles employed for fighting and fertilization, there are many various types of antennae, including filliform, moniliform, and incrassate, which at the top part gradually evolve with geniculate, serrate, pectinate, flabellate, clavate, and lamellate that feel and act.
Prothorax, Mesothorax, and Metathorax are the three sections that make up the thorax. In Coleoptera, the prothorax is consistently well-developed and made up of a sizable dorsal sclerite. The front mesothorax is covered by the pronotum, which continues ventrally on each side to meet the lateral pleura. Usually big, sclerite, and situated on the back wing is the metasternum. Beetles’ legs are typically designed for running or walking, and they typically get bigger from front to back. However, some families of beetles may have one or more pairs of legs modified for other activities, such as digging in soil (Scarabaeidae and Tenebrionidae), tunnelling through the wood (Bostrichidae, Platypodine, Scolytine, and Curculionidae), swimming (Dytiscidae, Gyrin (Eucinetidae and Chysomelidae). Significant taxonomic characteristics are provided by the shape and degree of separation of the coxae. (Lawrence et al., 1995).
There are two sets of wings. Elytra are used for forewings and membranes for hind wings. Coleoptera has hind wings that are almost usually longer than the elytra and are folded transversely and longitudinally when at rest. For them to be hidden beneath the elytra’s thickening and hardening into a shell-like covering. The elytra typically have parallel anterior sides and a tapered posterior. They can also be more or less hemispherical or oval. The wings may be reduced to minimal traces, folded but not shortened, or completely missing. Due to the degradation of the flight muscles that occurs during an insect’s life in conjunction with the development of the gonads, certain beetles with fully grown wings may be unable to fly (Lawrence and Britton, 1991).
Males typically have 10 segments in their abdomen, whereas females often have 9 segments. Segment tenth in males is frequently greatly decreased or united with segment nine, which is changed to form the genital segment. In most adult beetles, the terga eighth can be mounted on the dorsal surface of the abdomen if the genital segment is excluded. Even though certain flightless species make it more difficult to identify the terga, their number can still be easily ascertained by counting the spiracles beginning with the larger one at the base of the abdomen. A tergite, a prominent plate found on each tergum, may or may not be flanked by a second pair of laterotergite sclerites. Each abdominal segment contains strong tergite and sternite articulate on the dorsal and ventral, and the spiracles are typically found in the pleural membrane. The abdominal segment occurred secondary segmentation process. (1991; Lawrence and Britton)
Beetles are holometabolous insects, and they go through four phases of development before becoming adults. Typically, Adult beetles can be identified by their heavily sclerotized forewings, or “elytra,” which serve as a powerful defense barrier (Balke et al., 2002).
Eggs can vary in shape, have a lifespan of 8 to 12 days, can be laid singly or in groups, and are typically laid at a location that allows the larva to develop properly, such as in the bark of a tree or on the leaf of a host plant (leaf-eating species). Eggs may also be placed next to roots, in fruit, flowers, tree wounds, on water plants, or beneath rocks (Lawrence and Britton, 1991). Diorhabda carinulata’s Chysomelidae family females lay 10–20 eggs each day, producing 300–500 eggs total. The eggs hatch in 7 days (Lewis et al., 2003).
The larvae of coleopterans come in several varieties. Grubs in the first, second, and third instars range in age from 10 to 165 days. The following characteristics set coleopteran larvae apart from those of the majority of other endopterygotes: a well-developed and typically sclerotized head; a lack of frontal ridges; and antennae with four or fewer segments. 4 to 6 stemmata or less 5. The body of a carabid larva is smooth, flattened, and tapering. Click beetle (Elateridae) larvae have a rough surface and are cylinder-shaped or flat and thin. Soft-bodied and slender Buprestidae larvae tunnel under tree bark or burrow under the surface of leaves. (1991; Lawrence and Britton). The adults of the Curculionidae family (Otiorhynchus sulcatus) live for 63 days and feed on the foliage, causing damage that is distinctly theirs. The larvae feed underground on roots (John and Lattin, 1998). Chysomelidae (Diorhabda carinulata) larvae have three instars, with the first lasting 4–7 days, the second lasting 4-6 days, and the third lasting between 3–7 days, measuring 5–9 mm in length. The third instar forms a pupal case, which is made of loose silk cells and plant debris, and the pupal stage lasts 7–10 days (Lewis et al., 2003).
Pupae have a four-day or longer lifespan and live for 17–30 days. From egg to adult, the life cycle takes 21 to 27 days. Adecticous and almost invariably exarate, beetle pupae (obtect in Staphylinidae, Clambidae, Coccinellidae, Hispidae, Chysomelidae, and a few other groups). The abdomen typically has nine terga and sterna, and there are typically fewer spiracles than there are in the larva and adult. Numerous prominences and setae are frequently present on the head and body, which are used to keep the pupa away from the pupal cell walls. (1991; Lawrence and Britton).
Adults have a maximum lifespan of 230 days. The average number of eggs laid by females is around 3, ranging from 63 to 228. There could be several generations each year. Life cycles can last for substantially longer times, even up to four years or more, in cooler temperate regions. In general, species that feed on leaves have shorter life cycles than those that depend on wood or roots. Tropical and subtropical species are capable of having multiple generations per year. (1991; Lawrence and Britton). Diorhabda carinulata newly emerged adults (which are 5-6 mm long and 2.5 mm wide) feed and mate right away. Active adults move to nearby tamarisk trees to leave food for offspring. Adults secrete pheromones to promote aggregation and mating. Females lay eggs on tamarisk foliage every day after becoming mature. Adults live for 2-4 weeks after emerging in either late spring or early fall. There are two generations per year (Lewis et al., 2003).
Frequently Asked Questions
Question: Is beetle harmful to humans?
Question: Where does the beetle found?
Ans: Nearly all natural environments, or vegetative foliage, including trees and their bark, flowers, leaves, and underground near roots, as well as inside plants like galls and tissue from dead or decomposing ones, are home to coleoptera.
Question: Can beetles bite?
Question: What is the world’s heaviest insect?
Ans: A rhinoceros beetle
Question: What’s the fastest insect?