Intro to Entomology

Economic reasons to study insects

Insects affect human economies by destroying crops, contaminating stored food, and infesting livestock and structures; examples include locust swarms, grain weevils, and termites.

Medical reasons to study insects

Many insects transmit human and animal diseases—fleas spread plague, mosquitoes transmit malaria and yellow fever, and flies spread filariasis and other pathogens.

Biological abundance and diversity of insects

Insects make up over half of all known species, with an immense variety in form, habitat, and function; their total biomass surpasses that of all vertebrates combined.

Food-web dynamics

Insects serve as herbivores, decomposers, predators, and prey, recycling nutrients and sustaining ecosystems; birds, reptiles, and fish depend heavily on them as food sources.

Insect products and pollination

Humans use insect products like honey, silk, shellac, and dyes; pollinating insects such as bees are vital for fruit and crop reproduction.

Scientific importance of insects

Insects are key model organisms for research in genetics, physiology, ecology, and evolution because of their diversity and short life cycles.

Aesthetic value of insects

Butterflies, beetles, and fireflies provide beauty and inspiration in art, culture, and conservation.

Tagma

The main body divisions of insects: head, thorax, and abdomen, each specialized for different functions such as sensing, locomotion, and reproduction.

Exoskeleton

A rigid external covering made of chitin and proteins that protects the insect, prevents desiccation, and provides muscle attachment; must be molted for growth.

Integument

The entire body covering, including the living epidermis and the non-living cuticle layers above it.

Sclerites

Hardened plates of the exoskeleton that give structural strength; joined by flexible membranes for movement.

Basement membrane

Thin layer beneath the epidermis separating it from internal tissues and serving as a foundation for secretion of new cuticle.

Epidermis

Single layer of living cells that secretes and repairs the insect's cuticle; plays a role in molting.

Cuticle

Non-cellular outer layer secreted by the epidermis; includes the waxy epicuticle and the supportive procuticle.

Epicuticle

Thin, outermost waterproof layer that prevents dehydration and protects against chemicals.

Procuticle

Thicker inner portion of the cuticle made of chitin and proteins that provide strength and flexibility.

Chitin

Long-chain polysaccharide forming the framework of the exoskeleton, similar in structure to cellulose but with nitrogen groups.

Sclerotin / Sclerotization

Proteins and the chemical process that harden the cuticle through cross-linking, increasing durability and color.

Consequences of exoskeleton

Allows strength and protection but restricts growth, requiring periodic molting and limiting body size.

Labrum

Upper lip that helps hold and manipulate food during feeding.

Mandibles

Paired, jaw-like mouthparts used for biting, chewing, and cutting solid food.

Maxillae

Paired mouthparts that manipulate food and assist mandibles; each bears a sensory palp.

Labium

Lower lip structure that assists food handling and supports palps.

Palps

Sensory appendages on maxillae or labium that detect taste and texture.

Antennae

Paired sensory appendages detecting chemical cues (smell), movement, humidity, and sometimes sound.

Scape, Pedicel, Flagellum

Three main antenna segments—scape (base), pedicel (middle, often with sensory organs), flagellum (distal section, may have many subsegments).

Compound eyes

Large eyes made of many ommatidia providing wide field vision and motion detection; capable of perceiving color and ultraviolet light.

Ommatidium

A single visual unit in a compound eye, containing a lens, photoreceptor cells, and pigment cells.

Ocelli

Simple eyes that detect light intensity and aid in maintaining equilibrium; not image-forming.

Stemmata

Simple larval eyes capable of basic image formation; used by holometabolous larvae.

Thorax

Middle body region composed of three segments (pro-, meso-, metathorax) bearing legs and wings.

Leg segments

Five parts: coxa (base), trochanter, femur, tibia, and tarsus (foot).

Saltatorial legs

Adapted for jumping; characterized by enlarged femurs (e.g., grasshoppers).

Raptorial legs

Modified for grasping prey (e.g., praying mantis).

Cursorial legs

Adapted for running (e.g., cockroaches).

Natatorial legs

Modified for swimming with flattened tibiae or tarsi (e.g., diving beetles).

Fossorial legs

Adapted for digging with broad, spade-like segments (e.g., mole crickets).

Wings

Cuticular extensions used for flight; supported by a network of veins carrying nerves and hemolymph.

Apterygota

Primitive wingless insects that never possessed wings.

Pterygota

Winged insects or their descendants, representing most modern species.

Wing veins

Reinforcing tubes within wings that support structure and distribute hemolymph.

Halteres

Small, club-shaped hindwings in flies acting as gyroscopic balance organs.

Elytra

Hardened forewings that protect the membranous hindwings (beetles).

Hemielytra

Forewings partly hardened at the base and membranous at the tip (true bugs).

Tegmina

Leathery forewings providing protection but limited flight aid (grasshoppers, roaches).

Wing pads

Developing wings of immature nymphs in hemimetabolous insects.

Abdomen

Posterior body region containing digestive, excretory, and reproductive organs.

Cerci

Paired sensory appendages at abdomen tip that detect air currents or serve as pincers.

Aedeagus

Male copulatory organ for transferring sperm to female.

Ovipositor

Female organ used for laying eggs or modified into a sting (wasps, bees).

Prolegs

Fleshy, unsegmented legs found on caterpillars and larvae for gripping surfaces.

Rectal gills

Aquatic adaptations in larvae allowing gas exchange in the rectal area.

Spiracles

External openings that connect to the tracheal system for gas exchange.

Tracheae

Branching air tubes delivering oxygen directly from spiracles to tissues; bypass circulatory system.

Tracheoles

Microscopic tubes delivering oxygen to individual cells for efficient respiration.

Air sacs

Enlarged tracheae that store air and facilitate ventilation during flight.

Passive ventilation

Diffusion of gases through tracheae without muscular movement.

Active ventilation

Body muscle contractions that push air through tracheae, common in flying insects.

Hemolymph

Insect 'blood' circulating in open system; transports nutrients, hormones, wastes, and immune cells.

Hemocoel

Main internal body cavity where hemolymph bathes organs directly.

Hemocytes

Cells in hemolymph that provide immunity, phagocytosis, wound repair, and encapsulation of parasites.

Open circulatory system

Circulatory system without closed vessels; hemolymph flows freely around organs.

Phagocytosis

Process where hemocytes engulf bacteria or debris as immune defense.

Encapsulation

Immune response where large parasites are surrounded by hemocytes and sealed off.

Dorsal vessel

Primary circulatory organ running along back; includes heart (pulsatile) and aorta (non-pulsatile).

Ostia

Valved openings through which hemolymph enters the heart chambers.

Fat body

Tissue that stores energy reserves, detoxifies, and aids metabolism; comparable to vertebrate liver and fat.

Luminescence

Light production via chemical reactions (e.g., luciferin-luciferase system in fireflies).

Alimentary canal

Digestive tract from mouth to anus; divided into foregut, midgut, and hindgut.

Foregut

Region for ingestion, food storage, and initial digestion; includes mouth, pharynx, esophagus, and crop.

Midgut

Main site of enzymatic digestion and nutrient absorption.

Hindgut

Area for water and salt reabsorption and fecal formation.

Gastric caeca

Blind-ended pouches in midgut that secrete digestive enzymes and increase surface area.

Symbionts

Mutualistic microbes living in gut that aid digestion or synthesize nutrients.

Malpighian tubules

Excretory organs filtering hemolymph and excreting nitrogen waste into gut for elimination.

Ammonia, Urea, Uric acid

Nitrogenous waste products; uric acid conserves water and is common in terrestrial insects.

Parthenogenesis

Reproduction without fertilization; offspring are genetically identical to the mother, allowing rapid population growth but low genetic variation.

Bisexual reproduction

Involves both male and female parents, promoting genetic diversity through sexual recombination.

Testis

Male reproductive organ that produces and stores sperm.

Male accessory glands

Produce seminal fluid and proteins that nourish sperm and influence female physiology after mating.

Spermatophore

Package of sperm (and sometimes nutrients) transferred from male to female.

Ovary

Female organ producing ova (eggs).

Oviduct

Tube carrying eggs from ovaries to outside the body.

Spermatheca

Storage sac in female reproductive tract that holds sperm for later fertilization.

Egg

Female reproductive cell containing yolk and protective layers for embryonic development.

Yolk

Nutrient supply for developing embryo.

Chorion

Protective outer eggshell layer.

Micropyle

Tiny opening in egg allowing sperm entry for fertilization.

Oviparous

Eggs laid externally; embryo develops outside female body.

Viviparous

Embryo develops inside female; live young are born.

Ovoviviparous

Eggs develop and hatch inside female, producing live young.

Neuron

Basic nerve cell transmitting electrical impulses; composed of soma, dendrites, and axon.

Axon

Long fiber that conducts nerve impulses away from the cell body.

Dendrites

Branching structures receiving signals from other neurons.

Synapse

Junction where nerve impulses pass between neurons using neurotransmitters.

Acetylcholine (ACh)

Primary neurotransmitter in insects; transmits nerve impulses across synapses.

Acetylcholinesterase

Enzyme that breaks down acetylcholine to stop signal transmission; target of many insecticides.

Ganglia

Clusters of nerve cell bodies controlling body segments independently.

Brain

Central processing center consisting of protocerebrum (vision), deutocerebrum (antennae), tritocerebrum (mouthparts).

Ventral nerve cord

Main longitudinal nerve structure with paired ganglia along the insect's underside.