Coleoptera: what are they, characteristics, types and examples

The Coleoptera (word that originates from the Greek koleos , which means “box or case”, and from the Greek pteron , which means “wing”) or also called beetles , form an order of holometabolic insects known as Coleoptera . Taxonomically speaking, they form more than 40% of the diversity described for Hexapoda worldwide, between 360,000 and 400,000 currently described species are known . Thus, it includes a quarter of all the species described so far and, in addition to being the zoological group with the largest number of species in the entire biosphere, it is the most diverse order of animals on the planet.

Beetles are a monophyletic group, with the oldest coleopteroid fossil dating to the Lower Permian (270 million years ago). However, the first true Coleoptera appeared in the Upper Permian stage (about 250 million years ago) and in the Upper Triassic (240-220 million years) where up to twenty families are recognized.

We invite you to learn more about the Classification of insects with this other post from AgroCorrn.

Coleoptera are characterized by presenting great morphological variability, a characteristic that has allowed them to colonize all types of environments and habitats, from freshwater to marine environments. This has made them the group of animals with the greatest evolutionary success. But what are coleopterans like ? These are the main characteristics of coleopterans :

• Like insects, the body of beetles has three characteristic tagmas: the head, the thorax and the abdomen. However, the existence of a pterothorax covered by the elytra (totally hardened modified wings with a protective function to the second pair of wings, the posterior part of the thorax and the abdomen), gives the sensation that the body is divided into an anterior part, formed by the head and the prothorax, and a posterior one under the elytra.
• Typically, the head is porgnata, ie the longitudinal axis of the rest of the body coincides with the head (angle 180 ^or ). It is endowed with a cephalic capsule, where the following regions are distinguished: the forehead, the vertex between the forehead and the occiput and some lateral areas known as genas, where the compound eyes are located. In this capsule, a pair of antennae and the mouthparts are connected, the latter endowed with an orthopterid structure that facilitates chewing.
• The thorax is characterized by a sharp division into the prothorax and pterothorax. The first section is free while the second forms a functional unit. The metathoracic wings are membranous and fold transversely below the elytra, being normally longer than the elytra.
• The abdomen is divided into ten or eleven segments, of which there are 5 or 6 visible sternites (corresponding to segments III to VII or VIII).
• Regarding the size of the individuals, this usually oscillates between 0.3 mm of some Ptiliidae and 200 mm of the females of Titanus giganteus and Xixuthrus heros (Cerambycidae).

Regarding the diet of these organisms, there is a very diverse range of food sources, as varied as their ways of life. Coleoptera can feed on flowers, fruits, manure, other animals, seeds, leaves, pollen, roots, among many other options. In fact, the typology of their diet allows them to be classified into three suborders of coleopterans according to their diet :

• Suborder Adephaga , or Carnivorous Coleoptera.
• Suborder Myxophaga , or Herbivorous Coleoptera.
• Suborder Polyphaga , or Omnivorous Coleoptera.

Commonly, coleopterans reproduce sexually , while parthenogenesis occurs exceptionally.

It all starts when males attract females through aggregation hormones while females attract males through pheromones or, also, emitting sounds. They court and then breed. From there, a very variable size and number of eggs is produced , from a large one to several hundreds or thousands of small eggs. Their life cycles are usually univoltinous; however, in warm areas and with enough food, two or more generations can occur per year.

4 suborders are considered: Archostemata, Myxophaga, Adephaga and Polyphaga . The suborders that contain coleopteran species of agricultural interest are Adephaga and Polyphaga and, therefore, we focus on these.

• Adephaga: Developed coxas that divide the first abdominal segment. Notopleural suture present. Tarsal formula 5.5.5.
• Polyphaga: Developed coxas do not divide the first abdominal segment. Notopleural suture absent.

Some examples of more curious beetles are the titan beetle ( Titanus giganteus ), which can reach a size of 17 centimeters, the eastern firefly ( Photinus pyralis ), characterized by emitting bioluminescence, and the cantharid ( Lytta vesicatoria ), one of the species of beetle poisonous to humans. And there is still an immensely curious and peculiar variety of coleopteran species

There are several species of coleopterans that can cause damage to horticultural crops or garden plants , making them potentially pest-causing animals.

A common example is coleopteran pests on rapeseed. Normally, this event is evident when the larvae have emerged from the rapeseed pods through openings. Previously, inside the pod, these larvae have eaten the grains of the pods. Consequently to the perforations that they create in the pods, the water penetrates inside them causing outgrowths.