MODULE 2 : The Science of Entomology

Veterinary Entomology

Deals with arthropod pests and vectors of disease agents affecting livestock, poultry, pets, and wildlife, allied with Medical Entomology, Parasitology, Animal Sciences, Veterinary Medicine, and Epidemiology.

Main Pests of Veterinary Concern

Sucking and biting lice, biting flies, non-biting muscoid flies, bot flies, fleas, and Acari (mites and ticks).

General Characteristics of Arthropods

Bilateral symmetry, triploblastic body derived from ectoderm, mesoderm, and endoderm, found on land, in water, and in soil, jointed limbs, body segmented into head, thorax, and abdomen.

Integument

Body covering made of chitin, composed of cuticle and underlying epidermal cells that secrete the cuticle, forms the insect's exoskeleton, provides muscle attachment and the first line of defense against fungi, bacteria, predators, parasites, and environmental chemicals, including pesticides.

Sclerites

Typical body segments formed by the chitinous integument, divided into tergum (dorsal), sternum (ventral), and pleuron (lateral).

Circulatory System of Arthropods

Composed of the hemocoele, a blood-filled space that bathes all body organs, an enlarged dorsal blood vessel (heart), pericardium enclosing the heart, paired ostia in the pericardial walls, and short arteries.

Respiration in Arthropods

May involve gills (bronchiae), tracheae, book lungs, book gills, and spiracles.

Gills (Bronchiae)

Respiratory structures found in larvae, nymphs, and adults of various aquatic species.

Trachea

Fine, elastic tubes in the chitinous lining that branch and ramify among the internal organs.

Book Lung

Respiratory structure found in spiders.

Book Gill

Respiratory structure found in crabs.

Spiracle

Small, circular opening in the exoskeleton.

Foregut (Stomodeum)

Consists of the buccal cavity, pharynx, proventriculus, and gizzard, involved in ingestion, passage, and disintegration of food particles.

Midgut (Mesenteron)

Responsible for food storage and enzyme secretion.

Hindgut (Proctodeum)

Responsible for absorption of food and expulsion of fecal materials.

Paired Nephridia

Excretory structures that remove metabolic wastes in crustaceans.

Malpighian Tubules

Excretory and osmoregulatory system found in some insects, myriapods, arachnids, and tardigrades.

Coxal Glands

Structures for collecting and excreting urine in arachnids and other chelicerates.

Nervous System of Arthropods

Consists of the supraesophageal center (brain) and ganglionated ventral nerve cord.

Male Reproductive System of Arthropods

Consists of paired testes, vas deferens, paired seminal vesicles, and penile organ.

Female Reproductive System of Arthropods

Consists of paired ovaries, oviduct, uterus, vagina, and spermatheca.

Indirect or Complete Metamorphosis (Holometabolous Life Cycle)

Has four stages: egg, larva, pupa, and adult. The hatched insect differs morphologically from the parent. Each form after ecdysis is called an instar. Example: mosquitoes.

Direct or Incomplete Metamorphosis (Hemimetabolous Life Cycle)

One or two stages are missing, except for the adult. The hatched insect, called a nymph, resembles a miniature adult. Examples: lice and bedbugs.

Egg Stage

Stage that undergoes a series of segmentation.

Larva

Developing form that emerges from the egg before transformation into a pupa, serving as the feeding stage of the parasite.

Pupa

Quiescent stage of metamorphosis that emerges from the larval stage.

Nymph

Form that emerges from the egg and resembles the adult in morphology.

Adult

Reproductive stage of the parasite.

Imago

The young adult.

Polypod Larva

Larva with a marked head, three-segmented thorax with legs, ten-segmented abdomen, and pairs of abdominal or fleshy hooked legs. Example: caterpillars.

Oligopod Larva

Larva with a well-marked head, three pairs of thoracic legs, and no abdominal legs. Example: beetles.

Apodous Larva

Larva with no legs on the thorax or abdomen. Example: maggots.

Free or Exarate Pupa

Pupa in which the wings and legs are free from the body and externally visible. Example: beetles.

Obtectate Pupa

Pupa with legs and wings bound to the body by molting fluid but still externally visible. Example: mosquitoes.

Coarctate Pupa

Pupa enclosed by the hardened last larval skin (puparium), so the pupa cannot be seen externally.

Oviparous

Female that lays undeveloped eggs. Examples: houseflies and stable flies.

Ovoviviparous

Female that lays larvated eggs.

Viviparous or Larviparous

Female that lays fully developed larvae. Examples: flesh flies, tsetse flies, and Oestrus ovis.

Pupiparous

Female that lays a larva that immediately turns into a pupa. Example: pigeon louse fly.

Parthenogenetic

Reproduction without males or fertilization. Examples: silkworm and Strongyloides sp.

Crustacea

Main body divisions are cephalothorax and abdomen, with legs on thoracic and abdominal segments.

Arachnida

Adults have four pairs of legs, two pairs of mouthparts, and no antennae or wings.

Pentastomida

Adults have no legs, except for two pairs of hooks near the mouth, while larvae have two pairs of legs.

Insecta

The largest group of arthropods, with adults having three pairs of legs and a body divided into head, thorax, and abdomen.

Diplopoda

Myriapods with an elongated, cylindrical body, terrestrial habitat, numerous segments each bearing two pairs of legs, and one pair of antennae.

Chilopoda

Myriapods with a long, narrow, dorsoventrally flattened body, several segments, and one pair of jointed legs per segment.