WHAT IS AN INSECT
EXTERNAL ANATOMY
GROWTH 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 Types
Chewing & 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 wings
Development 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
WITHOUT
METAMORPHOSIS
ORDERS
Thysanura
Microcoryphia
• 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)
GRADIAL
METAMORPHOSIS
ORDERS
Orthoptera
Blattodea
Mantodea
Phasmida
Isoptera
Dermaptera
Embioptera
Pscoptera
Phthiraptera
Hemiptera
Odonata*
Plecoptera*
Ephereroptera*
• 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
COMPLETE
METAMORPHOSIS
ORDERS
Thysanoptera
Neuroptera
Coleoptera
Mecoptera
Trichoptera
Diptera
Siphonaptera
Hymenoptera
Lepidoptera
• 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
• 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 oxygencontaining 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