Beetle Orders and Taxonomy Guide

• Beetles belong to the order Coleoptera.
• Have chewing mouthparts.
• Undergo complete metamorphosis.
• Have two pairs of wings, with the first pair hardened and the second pair membranous.
• Beetles are the largest order of insects.
• Public health issues caused by beetles are minor.
• Adults and larvae of some species occasionally bite.
• A greater number of beetle species secrete irritant chemicals.
• Some beetles cause inhalation allergies.
• Beetles can serve as intermediate hosts for helminths.

Taxonomy

• Beetles have sub-orders: Archostemata (most primitive), Adephaga (carnivorous with defensive glands), Myxophaga (algae eaters), and Polyphaga (largest and most diverse feeding habits).
• There are 165 families of beetles.
• North America is home to 130 beetle families.
• 350,000 beetle species are known, constituting 40% of known insects.
• North America has about 30,000 beetle species.
• Less than 100 beetle species are of public health importance, primarily within the Polyphaga suborder.

Life History

• Exhibit holometabolous development.
• Hypermetamorphosis occurs in some species.
• Overwintering happens either in the pupal or adult stage.
• They experience diapause.

Behavior and Ecology

• Beetles thrive in terrestrial and freshwater habitats.
• They possess diverse feeding behaviours: Saprophages, Herbivores, Carnivores, Omnivores.
• Mouthparts can play a role in human biting.
• Have defense mechanisms.
• Consume stored food, food debris, dead insects, and organic materials.
• Can cause skin irritation in humans.
• Some are respiratory allergens.
• The bombardier beetle is known for its defense mechanism.
• They may be attracted to artificial lights.
• Infestations result in skin irritation, allergies, or helminthic issues.

Public Health Importance

• Can cause skin, eye, ear and nose irritations.
• Some cause respiratory allergies.
• Can cause minor gastrointestinal discomfort.
• Example families include: Blister beetles, false blister beetles, some rove beetles, darkling beetles
• Tissue invaded by beetle larvae is called Canthariasis.
• Tissue invaded by adult beetles is called Scarabiasis.

Beetle Families of Medical-Veterinary Importance

• Meloidae (Blister beetles): cause eye irritation and blisters on skin; can poison and kill horses and birds that ingest them.
• Staphylinidae (Rove beetles): causes skin and eye lesions; can poison livestock that ingest them; some bite humans; attracted to dung.
• Scarabaeidae (Dung beetles and chafers): Spines cause irritation to the ears; intermediate hosts of helminths; dung feeders disseminate pathogens and remove dung.
• Tenebrionidae (Darkling beetles): cause skin and eye irritation; grain-feeding species are intermediate hosts of helminths and disseminate pathogens.
• Dermestidae (Larder, pantry, hide, carpet beetles): larval setae cause skin, eye, ear, and nose irritation; grain-feeding species are intermediate hosts of helminths; carrion-feeding species disseminate pathogens.
• Histeridae (Hister beetles): Beneficial as predators of fly eggs and larvae, they also develop in avian and mammalian manure
• Oedemeridae (False blister beetles): Cause skin and eye irritation.
• Carabidae (Ground beetles): Intermediate hosts of poultry tapeworms.
• Silphidae (Burying or carrion beetles): Potential disseminators of pathogens.
• Corylophidae (Minute fungus beetles): Cause eye lesions.
• Melyridae (Soft-winged flower beetles): cause skin tingling, numbing, and burning of the skin and eyes.
• Coccinellidae (Ladybird beetles or ladybugs): Secretions cause skin discoloration and irritation.
• Cleridae (Checkered beetles): Can bite humans, causing temporary distress.
• Cerambycidae (Long-horned beetles): Larger species can bite humans and other animals, causing temporary discomfort.
• Merycidae (Old World cylindrical bark beetles): can bite humans, causing temporary distress.
• Curculionidae (Weevils): Grain-inhabiting species can cause inhalational allergies.

Blister Beetles

• Medium-sized, 12.5-25.0mm long beetles.
• Conspicuously bright metallic blue, green, black, yellow, or brown.
• When disturbed, they emit a fluid containing cantharidin, an irritant.
• Touching them can irritate the skin.
• Have an unusual life cycle.
• The female lays a large number of eggs, often 2,000-10,000 on the ground or in the soil.
• Long-legged larvae hatch from these eggs and attack other insect eggs.
• They feed upon the eggs and undergo different larval forms, then pupate and become adults.
• Terpene cantharidin (C10H12O4) is secreted.
• Cantharidin in hemolymph is poisonous to humans.
• Cantharidin, when ingested, causes kidney damage and death.
• It produces extremely toxic effects on the urogenital system.
• Inflammation causes painful urination, hematuria, and persistent penile erection.
• Blister beetles are most often on flowers or foliage.
• Pose more risk to agricultural workers or soldiers.
• Cantharidin can be retained in frogs and birds potentially leading to human poisoning.

Oedemeridae (False Blister Beetles)

• Can cause vesicular or bullous dermatitis.
• This dermatitis is most common in the United States, Central America, and the Caribbean region.
• They are attracted to flowers.
• Causes immediate burning of skin.
• Cantharidin is the toxic substance.

Staphylinidae (Rove Beetles)

• Pederin (C25H45O9N) is more potent than Latrodectus spider venom.
• Produces the most complex nonproteinaeous insect defensive secretion
• Pederin is synthesized by endosymbiotic gram-negative bacteria (Pseudomonas species) found in female Paederus spp.

Tenebrionidae (Darkling Beetles)

• Produce defensive secretions containing “quinones.”
• Adults of Blaps species (Middle East and Europe) secrete quinones that cause burning, blistering, and darkening of the skin.
• T. confusum and T. castaneum have been associated with severe itching.
• North American desert species (Eleodes genus) exhibit a headstand pose and exude quinones to repel predators.
• Most tenebrionids are scavengers on decaying or dry plant material.

Tribolium castaneum

• The genome is about 190 Mb and contains more than 16,400 genes.
• It is a member of the most species-rich eukaryotic order, a powerful model organism.
• Important pest to stored agricultural products.
• Evolved the ability to interact with a diverse chemical environment.
• Has large expansions in odorant and gustatory receptors, as well as P450 and other detoxification enzymes.
• Development is more representative of other insects than Drosophila.
• Retained more ancestral genes involved in cell-cell communication than Drosophila.

Genes relevant to pest and Tribolium biology

• Cys-loop ligand-gated ion channels: (24 genes)-additional nicotinic acetylecholine receptor (nAChR) subunits are a target of imidacloprid and other neonicotinoids (nAChRs), fibronil (GABARs) and avermectins (GluCls).
• Cytochrome P450 proteins (CYPs): Involved in metabolic detoxification of host plant allellochemicals and toxicants, and several are insecticide resistance genes.
• 85% of Tribolium P450s clustered in groups of 2-16 genes.
• C1 cysteine peptidase genes: Successfully exploits cereal grains in spite of arsenal of defensive allelochemicals, including inhibitors of serine peptidase digestive enzymes.
• Neurohormones and G-protein-coupled receptors: Insect neurohormones (9neuropeptidase, protein hormones and biogenic amines) control development, reproduction, behavior, feeding and many other physiological processes often by signaling through G-protein-coupled receptors (GRCRs).
• 20 genes encoding biogenic amine GPCRs in TC, 52 neuropeptide.
• 45 ligands of 72 GPCRs.