Insect Characteristics and Products

Insect Characteristics

• Insects belong to the Phylum Arthropoda, making them some of the most abundant and diverse organisms on Earth.
• Insects have a segmented, bilaterally symmetrical body, with a hard chitinous exoskeleton, and paired jointed appendages.
• Entomology is the study of insects.

Distinguishing Characteristics of Insects

• Insect bodies have three distinct regions: head, thorax, and abdomen.
• Insects have one pair of antennae, three pairs of legs, and often one or two pairs of wings.
• The mouthparts of insects typically consist of mandibles, a pair of maxillae, a labrum, and a labium.

Products from Insects

• Apiculture is the raising of honeybees (Apis mellifera) for honey, wax, and other products like royal jelly and swarms.
• Sericulture is the rearing of the silkworm (Bombyx mori) to produce silk.
• Shellac is a sticky brown resinous substance produced from the lac insects; used in polishes, insulators, buttons, sealing wax, and hairsprays.
• Cochineal is a red dye produced from dried and powdered cactus mealybugs, used in food coloring and cosmetics.
• Chitin is a substance found in insect exoskeletons and has potential as an anticoagulant or haemostatic agent for tissue repair in humans.

Branches of Entomology

• Insect Ecology studies the relationship between insects and their environment, focusing on their presence in ecosystems.
• Insect Morphology studies the body parts of insects and their functions, primarily examining external body parts.
• Insect Pathology deals with diseases that harm insects and utilizes disease agents or vectors to control harmful pests.
• Insect Physiology focuses on the various functions and behavioral systems within the insect body.
• Insect Taxonomy deals with naming and classifying insects, which remains an ongoing process due to many unidentified species.
• Insect Toxicology studies how insecticides and other chemicals affect insect physiology.
• Industrial Entomology focuses on raising insects for beneficial or commercial purposes, including the removal of harmful insects from homes and buildings.
• Medical and Veterinary Entomology focuses on public health and veterinary-related insects like mosquitoes, flies, and cockroaches.
• Biological Control Entomology uses natural enemies (insects) to control insect pests.
• Postharvest Entomology studies, controls, and practices managing insects that damage stored crops and products.
• Forensic Entomology uses insects to determine or estimate the time and place of human death for legal purposes.

Insect Mouthparts

• Mouthparts are located within the preoral cavity, which houses the true mouth and salivary gland openings.
• Functional mouthparts are classified as Entognathous and Ectognathous.
• Entognathous: mandibles and maxillae are recessed and hidden within lateral folds of the head (e.g., Protura, Diplura, Collembola).
• Ectognathous: mandibles and maxillae are visible; folds in the head are absent (e.g., Class Insecta).

Positions of Insect Mouthparts

• Hypognathous: mouthparts directed downwards (e.g., Orthopteroid insects like grasshoppers).
• Prognathous: mouthparts directed forward (e.g., some beetles like ground beetles).
• Opisthognathous: mouthparts directed postero-ventrally (e.g., Homopterans like cicadas).

Types of Insect Mouthparts

• Mandibulate (Chewing): basic mouthpart type with labrum, mandibles, maxillae, labium, and hypopharynx.
• Sponging: mandibles and maxillae are non-functional; remaining parts form a proboscis with labella (sponge-like apex).
• Chewing-Lapping: mandibles and labrum are of chewing type used for grasping prey or materials for nest building.
• Piercing-Sucking: one or more appendages are sharp for piercing plant or animal tissue to extract fluids.
• Siphoning: specialized for moths and butterflies; long coiled proboscis for feeding on liquids like nectar.
• Rasping-Sucking: cone-shaped beak formed from clypeus, labrum, parts of maxillae and labium.

Mandibulate (Chewing) Insect Mouthparts

• Labrum (upper lip): movable flap covering the mouth.
• Mandibles (upper jaws): paired, heavily sclerotized structures that move horizontally for chewing.
• Maxillae (lower jaws): paired, segmented structures behind mandibles.
• Labium (lower lip): consists of a proximal postmentum and distal prementum.
• Hypopharynx: unsegmented fleshy lobe that arises from the floor of the cranium.

The Thorax

• The thorax is composed of three segments: pro-, meso-, and metathorax.
• Mesothorax and Metathorax bear wings, collectively called the pterothorax.
• Prothorax: bears the first pair of legs (prothoracic legs).
• Mesothorax: bears the second pair of legs (mesothoracic legs) and the first pair of wings (forewings).
• Metathorax: bears the third pair of legs (metathoracic legs) and the second pair of wings (hindwings).

Thoracic Hardened Plates

• Notum: upper plate.
• Sternum: lower plate.
• Pleuron: side/lateral plate.

Insect Wings

• Outgrowths of the body wall located dorsolaterally on the mesothorax (forewings) and metathorax (hindwings).
• Typical wings are membranous, strengthened by sclerotized veins, and used for flight.
• Types of wings:
  • Elytra: thickened, hard forewings of beetles (Coleoptera), used for protection.
  • Hemielytra: combination of thickened and soft, flexible, transparent apex of true bugs (Hemiptera: Heteroptera) forewings.
  • Fringed Type: hair-like margins on central structure of thrips (Thysanoptera) wings.
  • Membranous Type: soft, flexible, translucent or transparent wings with prominent veins (caddisflies, dragonflies, lacewings).
  • Halteres: small knob-like structures on flies and mosquitoes (Diptera) used for balance instead of flight.
  • Tegmina: leathery forewings of grasshoppers, cockroaches, and earwigs that protect membranous hindwings and abdomens.

Insect Legs

• Sclerotized, segmented structures typically with six segments:
  • Coxa (coxae): the basal segment.
  • Trochanter: small segment following the coxa.
  • Femur (femora): usually the first long segment.
  • Tibia (tibiae): the second long segment.
  • Tarsus (tarsi): series of small segments beyond the tibia.
  • Pretarsus: claws and pad-like or seta-like structures at the apex of the tarsus.

Modifications of Insect Legs

• Cursorial: running legs (e.g., cockroach foreleg).
• Fossorial: digging legs (e.g., mole cricket foreleg).
• Raptorial: grasping legs (e.g., praying mantis foreleg).
• Saltatorial: jumping legs (e.g., grasshopper hindleg).
• Natatorial: swimming legs (e.g., water beetle leg).

The Abdomen

• Simpler in structure than the head and thorax; lacks segmented appendages.
• Contains principal viscera, including the alimentary canal, circulatory vessel, Malpighian tubules, fat body, and reproductive organs.
• Plays a crucial role in respiration, reproduction, digestion, excretion, and metabolism.
• Composed of a maximum of 10 or 11 segments.
• The first 8 segments typically have a pair of spiracles and a ganglion of the ventral nerve cord.
• Each segment usually has a dorsal tergum, a ventral sternum, and membranous lateral pleura (sing. pleuron).

Other Important Parts of the Abdomen

• Spiracles: external openings of the respiratory system, found along the sides of the thorax and abdomen.
• Tympanum: main auditory organ; often located on the first abdominal tergite of grasshoppers, but may be found elsewhere in other insects.
• Cerci: slender, pointed structures on the eleventh abdominal segment.

Explore the fascinating world of insects through this quiz that covers their key characteristics, anatomy, and the valuable products derived from them. Learn about the distinct segments of an insect's body and the roles of apiculture and sericulture. Ideal for students of entomology and biology enthusiasts.