ENT 561 – Insects affecting human and animal health

Introduction … continued

Peripheral Damage

• Quarantine and Restrictions

• Medical treatment problems (incorrect, treatment avoidance, etc.)

• Contamination

– Blood Donations

– Food Contamination

• Societal Costs

– Associated with damage

– Associate with damage prevention measures

In many cases, man has worsened problem

• Transportation of arthropods

• Transportation of pathogens • Transportation of pathogens in humans

• Transportation of pathogens in livestock, insects, other animals

• Justinian created the first plague: “Without the empire, the bread dole, the huge shipments of grain and cloth from Africa, it is difficult to imagine how the First Pandemic could ever have erupted.” Orent, 2004

In many cases, man has worsened problem

• Increased population densities

• Expansion into new areas

• Environmental Modification

• Artificial Selection

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Introduction to the Insects

Introduction to the Insects

The oldest known insect -- Rhyniognatha hirsti – known from a single fossil, 400 million years old. This is shortly after plants colonize land and this appears to be a herbivore.

Introduction to the Insects

Life on earth as a speciescape:

• About 1 million of the 1.1 million animal species are insects

• Estimates range from 5 to 80 million insect species are currently in existence.

Insect Species Composition

Reasons for insect success• Small size -there are many more niches for small organisms than for large

organisms. For instance, one insect could live solely on and in the seeds of a specific plant.

• Short life cycle - this allows many generations within a given time for selection and evolution to take place.

• Large reproductive ability - large numbers of offspring support a large variation for selection and evolution to act upon.

• Variation in the life style of different stages in an insect's life (e.g. caterpillar versus butterfly) reduces competition for resources within the species.

• Wings-the ability to fly is relatively rare outside insects and has allowed them to colonize freely.

• Sensory sophistication - the sensory capabilities of insects surpasses most other organisms.

• Evolutionary interactions with other organisms - coevolution leads to greater specialization and speciation.

• Adaptation of appendages - mouthparts, wings and legs have often become highly specialized.

Insects just are

• They are neither good nor bad

• They are not here to serve a purpose – They evolved here in response to selective pressures

• Only man thinks of insects as “beneficial” or “detrimental”.

Some benefits of insects• Plant pollination - Pollination by animals is more effective than by

wind. Most higher plants are pollinated by animals, usually insects such as bees, wasps, flies and beetles.

• Production of products - honey, bees wax and royal jelly, silk (produced by the caterpillar, Bombyx mori), shellac (a varnish produced by a plant bug), cochineal (red food coloring produced by a plant bug) and 'Spanish fly' (a beetle and supposed aphrodisiac). 

• Nutrient recycling - by detritus and dung feeders and particularly in Australia by termites.

• Maintenance of an ecological food chain in many systems.

• Human food - over 500 species of insects are used as food by humans -usually crickets, grasshoppers, beetle and moth larvae and termites. Miscellaneous - Indigenous peoples (e.g. from PNG) often used butterflies and brightly colored beetles as head or body decoration. Insect collecting is a common Western hobby and there is a small industry in arthropod pets.

Detrimental effects of insects

• Destruction or spoilage of food (both fresh and stored) and crops (including forests)

• Damage to goods - leather, paper, textiles, (by beetles, cockroaches, silverfish or moths), timber & structures (by termites, some ants, different sorts of  borers)

• Direct disease of humans or livestock • Disease vectors • Venoms, allergies, urticating hairs• Nuisance value - flies, ants • Phobias - such as arachnophobia

Classification of insects

Common Names of Insects

• Very commonly used by scientists and laymen alike.

• Often more descriptive than the scientific names e.g. “Yellow Fever Mosquito”

• No scientific validity.

• For Insects, most names are set by the Entomological Society of America

Features of Arthropods

• Exoskeleton - a hard protective covering around the outside of the body (divided by sutures into plates called sclerites)

• Segmented body - that allows movement • Jointed limbs and jointed mouthparts - that allow

extensive specialisation • Bilateral symmetry - whereby a central line can divide

the body into two identical halves, left and right • Ventral nerve chord - as opposed to a vertebrate nerve

chord which is dorsal • Dorsal blood vessel

Distinguishing Features of Insects vs. Other Arthropods

Insects Arachnids Crustaceans Centipedes Millipedes

Legs 6 8 Variable 1 pr/bs 2 pr/bs

Antennae 1 pr 0 2 pr 1 pr 1 pr

Body Divisions

3 2 Variable Many many

Wings 2 pr 0 0 0 0

Distinguishing Features of Insects vs. Other Arthropods

Insects Arachnids Crustaceans Centipedes Millipedes

Legs 6 8 Variable 1 pr/bs 2 pr/bs

Antennae 1 pr 0 2 pr 1 pr 1 pr

Body Divisions

3 2 Variable Many many

Wings 2 pr 0 0 0 0

Head

Head - Mouthparts

Mouthparts have evolved in many ways.

Insect Head: Antennae

• Antennae are primarily chemical (& sometimes sound) receptors

• Three basic segments:  the scape, pedicel and flagellum

• Flagellum made up of multiple flagellomeres

Many basic types of antennae

Aristate - pouch-like with a lateral bristle. Eg. House flies.

Capitate - abruptly clubbed at the end. Eg. Butterflies.

Clavate - gradually clubbed at the end. Eg Carrion beetles

Filiformis - thread-like shape. Eg. Cockroaches.

Geniculate - hinged or bent like an elbow. Eg. Bees/ants.

Monoliform - bead-like in shape. Eg Termites.

Serrate – saw toothed shape. Eg. Click beetles

Plumose - brush or feather-like shape. Eg Moths and mosquitoes.

Setaceous - bristle-like shape. Eg Dragonflies.

Insect Body: Thorax & Abdomen

Ventral = Underside

Dorsal = Topside

Insect Legs

Wings

Generic Mosquito Wing

Internal Anatomy

Insect Cuticle

Insect Life Cycles -- Ametabolous

• Like almost all insects, start with eggs.

• Immatures have the very same shape as adults

• Seen in the most primitive, wingless groups (not medically important)

Insect Life Cycles -- Hemimetabolous

• Start with an egg

• Immatures have similar shape with adults EXCEPT wings.

•Wings develop externally to body

•Immatures often live in the same habitat as adults

• Includes the more primitive winged groups (Bugs, Dragonflies, Grasshoppers, Roaches

Insect Life Cycles -- Holometabolous

• Start with an egg.

• Immatures have a very different shape from adults

• Body transition occurs in pupal stage.

• Pupal stages often double as a survival stage.

• Larvae and adults often inhabit different niches

• Includes the most advanced insects: flies, beetles, moths/butterflies, bees/ants, fleas.

Insect Development and Weather -- Light

• May control vegetation and therefore insect populations

• Important in orientation.

• Used for inflight control – especially for night-flying insects

• Photoperiod -stimulus for diapause initiation

• Many insects are nocturnal or diurnal

Insect Development & Weather - Temperature

• Body temperature of insects governs rate of growth

• Most insect activity and reproduction occurs between 15 -35o C

• Different stages may have different rates of development.

• Surviving extreme temperatures often requires special adaptations in physiology, behavior, etc.

• Understanding the relation between development & weather enables us to predict activity/threat level.

Insect Development & Weather - Wind

• Indirect effect causing evaporation, humidity and so desiccation

• Dispersal e.g. aphids, moths grasshoppers

• Often affects activity levels esp. for weak fliers.

• Affects distribution of olfactory stimulants for feeding, oviposition, and mating.

• Primarily a factor for adults.

Insect Development & Weather - Moisture

• Sometimes affects development directly.

• Rain important for those species that need ephemeral aquatic habitats.

• Humidity important as an antidessicant.

• Often interacts with temperature

When populations are too big, they must be controlled.

• Cultural – Habitat manipulation• Mechanical/Physical – swatting/picking,

exclusion, environmental manipulation, etc.• Biological – Using one species to control

another: Predators, parasitoids, pathogens

• Genetic – Applying a control on F1 which is expressed in F2 or later.

• Behavioral – Modifying the behavior• Chemical – Using lethal chemicals