por What are beetles?
The beetles or Coleoptera (Coleoptera) are the order of terrestrial or flying insects that have more species in the animal kingdom, with more than 380,000 species. They have a pair of modified wings. The first pair of rigid and sclerotized wings, called elytra, protect the abdomen and the second pair of membranous wings.
Commonly called beetles, they have a wide diversity of forms and are adapted to most terrestrial habitats.
These insects have a rigid and compact body, covered by an exoskeleton, being of variable sizes, from a few millimeters to 10 cm long. It presents from dark colors to compositions with bright, metallic and iridescent tones.
The body is segmented into the head, thorax and abdomen, even though they appear to be divided into two parts, due to the presence of the pterothorax. The chewing mouthparts, a pair of compound eyes, and a pair of antennae are located on the head.
Some species have protrusions of different shapes such as horns, jaws, antennae or spines, which come out of the exoskeleton.
The vast majority of beetles are herbivorous, and different species constitute pests of agricultural crops. The larvae are the main agents that cause most of the agricultural and forest damage.
Characteristics of the beetles
– It is the most numerous order of the Insecta class, with more than 380,000 described species, located in various ecosystems.
– They have forewings or elytra that protect the second pair of membranous wings. The membranous wings have a longitudinal and transversal folding system that facilitates flight.
– Their body is divided into three segments: head, thorax and abdomen, and they have three pairs of legs.
– They are of variable coloration, which often results from the environment where they live, from black and dark, to bright and metallic tones.
– His body presents a high degree of sclerotization, due to the accumulation and hardening of chitin in the exoskeleton.
– The size varies depending on the family, small like the Staphylinidae (2-10 mm) or large like the Scarabaeidae (2-180 mm).
– Most are herbivores, however, there are carnivores that feed on other insects or snails.
– The oral apparatus is chewing, both in larvae and adults, with some species having a sucking or licking system.
– They are holometabolous insects, of complete metamorphosis, in addition their reproduction is of the sexual type.
– They are oviparous, the female deposits eggs, of different shapes, sizes and colors, on particular structures of the plant.
– Generally, beetles do not cause any harm to humans, they even recycle organic matter or are used in biological pest control.
– Some species are considered agricultural, forestry, domestic and stored product pests, causing large economic losses.
beetle classification
The Coleoptera order is made up of a diversity of families categorized by their morphology and habits.
These families include: Elateridae, Buprestidae, Cucijidae, Coccinellidae, Meloidae, Tenebrionidae, Bostrichidae, Anobiidae, Scarabaeidae, Cerambycidae, Chrysomelidae, Bruchidae, Dermestidae, Lyctidae, Anthribidae, Curculionidae, and Scolytidae.
One of the most widely used classifications for its economic importance to humans is based on the predatory activity of beetles, and includes the families Anabiidae, Chrysomelidae, Curculionidae, Nitidulidae and Scolytidae.
Habitat and feeding
This group of insects are found in all habitats on Earth, including underwater, with the exception of the open sea. They are species of diurnal and nocturnal habits, that live in colonies or are solitary and wandering.
They live on the ground, under stones and among the fallen leaves of the forests. On plants in stems, foliage, flowers, and fruits, on or under fresh water, and in deserts.
There is a good number of species considered agricultural pests, of stored grains and at the domestic level, causing enormous economic losses.
For example, Chrysomelids are defoliating beetles, Curculionids are pests of processed foods, and Dermestids feed on textiles.
The diet of this immense group of individuals, including the larva and the adult, is as wide as its distribution. Its preferred food is living plants: roots, stems, leaves, flowers, pollen, fruits and seeds, causing defoliation, wounds and mutilations.
There are even species like the Hypothenemus hampeia beetle that drills and multiplies inside the coffee fruit, causing severe damage.
There are other species, like the Scarabaeus laticolliswhich feeds on decomposing organic matter and favors the dynamics of the ecosystem.
Types of beetles according to food
– Philophages: beetles that feed on the foliage of plants. This group includes the different pests of agricultural crops. For example: Family Chrysomelidae.
– Rhizophages: species that feed on the root system of plants. For example: Family Elateridae.
– Polinivores or polyphagous: they destroy flowers, since they feed on pollen. For example: Family Oedemeridae.
– Antófagos: they feed exclusively on flowers. For example: Subfamily Cetoniinae.
– Frugivores or carpophagous: they feed on the fruits.
– Xylophages: they cause damage in forest areas, since the larvae of certain species feed on wood. For example: Family Cerambycidaeo.
– Spermophages: feed on seeds. For example: Family Bruchidae.
– Fungivores or mycophages: they feed on fungi. For example: Family Ciidae.
– Predators: beetles that catch and eat other species of insects, such as snails, slugs and earthworms, being useful for biological control. For example: Family Staphylinidae.
– Saprophagous: they feed on leaf litter and decomposing plant debris. For example: Family Scarabaeidae.
– Coprophagous: they feed on mammalian excrement. For example: Subfamily Scarabaeinae.
– Ghouls: they feed on the corpses of other species. For example: Subfamily Silphidae.
Reproduction
Sexual reproduction is characteristic of Coleoptera. However, in some species parthenogenesis can occur, that is, the formation of a new individual without fertilization.
courtship and mating
The pre-mating ritual is essential for copulation to occur. The female emits a pheromone that attracts the male. Female pheromones are chemical compounds (fatty acids, amino acids or terpenoids) that affect the behavior of the male.
Other beetles, such as fireflies, use bioluminescence during courtship, a biochemical process that occurs in special organs located in the abdomen. The male flies or dances over the female, pats her back, and finally strokes her with her antennae until she accepts her union.
Generally, mating is short, with the exception of some species where it can last several hours. In this activity fertilization occurs, the male transfers the sperm to the female to fertilize the egg.
After mating and fertilization of the female, a few days later the eggs are ready to be laid. The females deposit the eggs in an appropriate substrate that guarantees food for the larvae at birth.
Lifecycle
The order Coleoptera, as a member of the superorder Endopterygota, is characterized by undergoing complete metamorphosis or holometaboly. The transformation process that occurs in Coleoptera occurs through four phases or stages: egg, larva, pupa, and adult.
Egg
Each female has the capacity to fertilize thousands of eggs during her life cycle. The eggs have a soft and smooth shell, semi-permeable, of size, shape and color depending on each species.
The oviposition of the eggs is characteristic of each family of Coleoptera. Some can be placed loose in the substrate, individual or grouped on the underside or upper side of the leaves, or buried in the ground.
In fact, some species provide special care to guarantee food and the survival of the new organisms. Some beetles build galleries in the substrate or inside leaves to protect the laid eggs.
Larva
The larvae develop and hatch from the fertile eggs. The beetles in the larval phase can pass from 3 to 5 instars, reaching up to 30 instars depending on the species.
In this phase, the formed individual has the function of feeding itself and keeping reserves for its next stage. The larvae eat, grow, and molt until they reach the pupal stage, in which they complete the complete metamorphosis towards the adult or imago.
pupa
Once the larva is ready to start the metamorphosis process, it builds a protective structure called a cocoon, where it remains immobile. Despite its inactive appearance, great changes occur within the pupa where the adult develops that will continue the life cycle.
Adult
The adult emerges from the pupa after having fully matured within the pupa, to start a new reproductive process. Adults may live for a season or several months, depending on the species and ecological conditions.
References
Alonso-Zarazaga, MA Order Coleoptera. IDE@-SEA Magazine.
Coronado, Ricardo and Marquez, Antonio. Introduction to Entomology: Morphology and Taxonomy of Insects. Editorial Limusa.