WHAT IS AN INSECT

EXTERNAL ANATOMYGROWTH AND DEVELOPMENT INTERNAL ANATOMY & PHYSIOLOGY

Body divided into three regions

HEAD– the head capsule is a sturdy compartment that houses the brain, a

mouth opening, mouthparts used for ingestion of food, and major sense organs (including antennae and compound eyes)

Insect Mouth TypesChewing & Biting Mouth Parts• Usually found on predatory insects, and those

that feed on vegetation

Mandibles

Piercing & Sucking mouth parts • Slender, tubular feeding and sucking organ used

to extract nectar from flowers• stabbing mouthparts used to extract fluids from

plants and animals • Mouth part is used as a sponge to suck up fluid

proboscis

THORAX– this region is almost exclusively adapted for locomotion– contains three pairs of walking legs – in many adult insects, one or two pair of wings – composed of three body segments: prothorax, mesothorax, and

metathorax

• ABDOMEN– segmented structure located just behind the thorax– Spiracles (opening to the respiratory system)– Digestive tract and male and female reproductive organs (genitalia)

EXOSKELETON

• serves as a protective covering over the body, also know integument • Provides the surface for muscle attachment • A water-tight barrier against desiccation • Sensory interface with the environment

MULTI-LAYERED STRUCTURE WITH FOUR FUNCTIONAL REGIONS: • Epicuticle, procuticle, epidermis,

basement membrane

EPIDERMIS• primarily a secretory tissue

formed by a single layer of epithelial cells

• Responsible for producing at least part of the basement membrane as well as all of the overlying layers of cuticle

BASEMENT MEMBRANE • Supportive bilayer that serves

as a backing to the epidermis• Effectively separates the

hemocoel (insect’s main body) from the integument

PROCUTICLE• Lies immediately above the

epidermis • Contains microfibers of chitin

surrounded by a matrix of protein • In some parts of the body,

procuticle stratifies into hard, outer exocuticle and a soft, inner endocuticle

Sclerotization – occurs after each molt in which a chemical process causes the protein matrix to “solidify” forming rigid “plates” of exoskeleton known as sclerites

Membranes are areas that remain soft and flexible and sclerotization does not occur because of higher amounts of resilin, an elastic protein

EPICUTICLE • Outermost part of the cuticle • Functions to reduce water loss

and block invasion of foreign matter

EXOCRINE GLANDS • Specialized epidermal cells • Large, secretory cells produce

compounds such as pheromones and repellants

MICROTRICHAE (PILE)• Tiny, hair-like projections

MACROTRICHAE (SETAE)• Larger hairs, bristles, and scales

SKELETAL MUSCLES • Attach to the inner surface of the

integument

MORPHOGENESIS

• All changes that involve growth, molting, and maturation Molting -periodic outgrowing and replacing of the exoskeleton Growth of wingsDevelopment of genitalia

METAMORPHOSIS• Insects’ lives are divided into a series of

stages: egg, one or more immature stages, and adult

• In most cases, the appearance of a given species changes drastically in each successive stage.

• The process by which one stage transforms into another is called, metamorphosis

• Insects undergo little, or no structural change as they grow older• Immatures are called young (similar to adults in every way except size and

sexual maturity)

ORDERS ThysanuraMicrocoryphia

WITHOUT METAMORPHOSIS

• insects exhibit gradual changes in body form • immatures are called nymphs or if aquatic, naiads• maturation of wings, external genitalia, and other adult structures occurs in

small steps from molt to molt • developmental changes that occur are visible externally as the insect grows,

but adults retain the same organs and appendages as nymphs (eyes, legs, mouthparts)

*aquatic immature stage

GRADIAL METAMORPHOSIS

ORDERSOrthoptera EmbiopteraBlattodea PscopteraMantodea PhthirapteraPhasmida HemipteraIsoptera Odonata*Dermaptera Plecoptera*

Ephereroptera*

• Insects have immature forms (larvae) that are very different from adults• Larvae are adapted mostly for consuming food and growing in size• While larvae will molt several times gaining size (instar), they do not

acquire any adult-like characteristics• When fully grown, larvae molt to an immobile pupal stage (pupa) and

undergo a complete transformation • Larval organs are digested internally and are replaced with new adult

structures• The adult stage, which usually bears wings, is mainly adapted for

dispersal and reproduction

COMPLETE METAMORPHOSIS

ORDERSThysanoptera Diptera Neuroptera SiphonapteraColeoptera HymenopteraMecoptera LepidopteraTrichoptera

• Caterpillars go through 5 stages of growth.

• Each stage is called an instar. • When the caterpillar becomes too

large for its skin, it molts. • A caterpillar will molt 5 times before

it becomes a chrysalis (pupa)

ENDOCRINE SYSTEM• Comprised of hormone secreting structures that help maintain

homeostasis, coordinate behavior, and regulate growth, development, and other physiological activities.

Hormone- a chemical signal sent from cells in one part of an organisms to cells in another part (or parts) of the same individual• Produced in small quantities but cause profound changes

DIGESTIVE AND EXCRETORY SYSTEM

• Insects use their digestive system to extract nutrients and other substances from the food it consumes.

• Insects have a complete digestive system occurring in a tube-like enclosure, the alimentary canal, running lengthwise through the body from the mouth to anus

• Ingested food only travels one way • Insects have salivary glands residing in the thorax

CIRCULATORY SYSTEM• Insects, like all athropods have an open circulatory system where is

hemolymph (blood) spends much of its time flowing freely within body cavities where it makes direct contact with all internal tissues and organs

• Responsible for movement of nutrients, salts, hormones, and metabolic wastes throughout the insects’ body

• It plays several critical roles in defense – Seals off wounds through a clotting reaction – It encapsulates and destroys compunsd that provide a degree of protection against

predators – It can cool the body by conducting excess heat away

Dorsal vessel is the major structural component of an insect’s circulatory system

RESPIRATORY SYSTEM• Insects are aerobic organism (they must obtain O2 from their environment• Responsible for delivery sufficient O2 to all cells of the body and for

removing CO2 that is produced as a waste from the circulatory system• In most insects, the respiratory system us separate from the circulatory

system• Tracheal system- is a complex network of tubes that deliver oxygen-

containing air to every cell in the body • Air enters through the spiracles and to the tracheal system

REPRODUCTIVE SYSTEM • Reproductive organs of insects are similar in structure and function to

those of vertebrates– A male’s testes produce sperm; a female’s ovaries produce eggs (ova)

• Some species of insects are able to reproduce by parthenogenesis, a from of asexual reproduction in which new individuals develop from unfertilized egg

• Advanced insects exhibit internal fertilization where males deposit their sperm inside a female’s body

THE NERVOUS SYSTEM • Insects have a relatively simple nervous system with a dorsal brain linked

to a ventral nerve cord• Nervous system is a network of specialized cells (neurons) that serve as

the “information highway” within the body• Neurons are divided into three categories, depending on their function

within the nervous system– Afferent (sensory) neurons – Efferent (motor) neurons – Internuncial (association) neurons

Side view of body showing relative position of circulatory (yellow), digestive (green), and nervous (blue) systems