Terrestrial Mandibulates

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Terrestrial Mandibulates

• Chapter 20

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Uniramia

• Uniramians are mostly terrestrial arthropods.
• A few live in freshwater.
• Only one pair of antennae.
• Appendages uniramous as adults.
• Tracheae carry respiratory gases directly to/from
  all body cells.

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Uniramia

• Myriapods (many footed) include Class Chilopoda,
  Diplopoda, Pauropoda Symphyla.
• Two tagmata head trunk.
• Paired appendages on most trunk segments.

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Uniramians

• Class Insecta
• Three tagmata head, thorax abdomen.
• Appendages on head thorax, reduced or absent on
  abdomen.

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Class Chilopoda

• Centipedes class chilopoda contain a few or
  many segments each (except the first behind the
  head and the last two) with a pair of jointed
  legs.
• Last pair of legs has a sensory function.

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Class Chilopoda

• Head appendages
• One pair antennae
• One pair mandibles
• One or two pairs of maxillae.
• Dorsoventrally flattened.

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Class Chilopoda

• Sexes are separate.
• Some lay eggs (oviparous).
• Some have live young (viviparous).
• Young like little adults no metamorphosis.

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Class Chilopoda

• Centipedes live in moist environments.
• They are carnivores, feeding on insects worms.
• Prey is killed with poison claws on the first
  segment.

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Class Diplopoda

• Millipedes (Class Diplopoda) have two pairs of
  legs on each segment.
• Head has one pair each of antennae, mandibles,
  maxillae.
• Body is more cylindrical.

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Class Diplopoda

• Millipedes live in dark, moist places under
  rocks or logs.
• Most are herbivores, feeding on decayed plant
  matter or occasionally living plants.
• Slow moving, coil up when disturbed.
• Toxic or repellent fluids secreted when disturbed.

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Class Insecta

• Insects are the most diverse and abundant of all
  arthropods.
• 26 orders
• Most are terrestrial or inhabit freshwater.
• Few are marine.

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Class Insecta

• Insects have
• 3 Tagmata head, thorax, abdomen.
• 3 pairs of legs and usually 2 pairs of wings on
  their thorax.

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Class Insecta

• Insects show a diverse array of morphological
  variation.
• They consistently have 3 tagmata.
• Head compound eyes, one pair antennae, 3
  ocelli, mouthparts (including mandibles
  maxillae)
• Thorax 3 segments each with a pair of legs, the
  last 2 segments usually have wings as well.
• Abdomen 9-11 segments

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Class Insecta

• Antennae can act as tactile organs, olfactory
  organs, and sometimes auditory organs.

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Class Insecta

• Legs have also become highly specialized for
  walking, grasping, skating over water, and
  specialized jobs like gathering pollen.

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Class Insecta

• Flight is one key to the great success of
  insects.
• An animal that can fly can escape predators, find
  food, and disperse to new habitats much faster
  than organisms that can only crawl.

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Class Insecta

• Insects are the only invertebrates that can fly.
• Most have two pairs of wings.
• Some are ancestrally wingless silverfish.
• Some are secondarily wingless fleas.

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Class Insecta

• The internal anatomy of an insect includes
  several complex organ systems.

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Insects - Nutrition

• Most insects are herbivorous, feeding on plant
  juices and/or tissues.
• Some are specialized, others will eat almost any
  plant.

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Insects - Nutrition

• Some insects are predaceous, catching eating
  other animals.

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Insects - Nutrition

• Other insects are scavengers or parasites.

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Insects - Nutrition

• Some insect parasites are parasitized by other
  insects hyperparasitism.
• Parasitoids are a lethal type of parasite.
• A tiny wasp lays eggs on the tomato hornworm.
  The wasp larvae will consume the hornworm.

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Insects - Nutrition

• Insects have mouthparts specialized for the many
  different foods they eat.
• Sucking mouthparts (mosquitoes) form a tube,
  can pierce animal or plant tissues.

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Insects - Nutrition

• Sponging mouthparts (house flies) liquid food
  is lapped up, food may be liquefied first.

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Insects - Nutrition

• Chewing mouthparts (grasshoppers) strong plates
  can tear food.

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Insects Circulation Gas Exchange

• Insects have an open circulatory system.
• Gas exchange is accomplished with a tracheal
  system an extensive network of thin-walled
  tubes that branch into every part of the body.
• Tracheal trunks open to the outside by spiracles.

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Insects Circulation Gas Exchange

• Insects spiders have independently evolved an
  excretory system of Malpighian tubules blind
  tubules opening into the hindgut.
• Potassium is secreted into the tubules and water
  diffuses in after it. Other solutes and wastes
  are secreted or diffuse into the tubules as well.

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Insects Circulation Gas Exchange

• Insects that feed on dry grains must conserve
  water and excrete salts.
• Leaf-feeders ingest excrete lots of fluid.
• Aphids pass fluid as honeydew that is consumed by
  other insects.

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Insects Sensory Organs

• Mechanoreception Mechanical stimuli are
  received by sensilla (simple or complex)
  distributed over the antennae, legs, and body.

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Insects Sensory Organs

• Auditory Reception Very sensitive setae or
  tympanal organs detect vibrations that come
  through the substrate or the air.
• Some moths detect ultrasonic pulses emitted by
  bats. They drop toward the ground in response to
  avoid the bats.

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Insects Sensory Organs

• Chemoreception Chemoreceptors for taste and
  smell are located in sensory pits on the
  mouthparts, antennae or sometimes the legs.

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Insects Sensory Organs

• Visual Reception Simple eyes (ocelli) are used
  to monitor light intensity, they do not form
  images.
• Compound eyes in insects, similar to those of
  crustaceans, consist of thousands of ommatidia,
  each having its own pigment cells and lens.

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Insects Sensory Organs

• Different insects have different capability to
  see color.
• Bees can distinguish most colors (they dont see
  red) beginning in the ultraviolet range.
• To us a flower may look uniformly colored, but to
  the bee there are lines that appear in the UV
  range that act as nectar guides.
• Other insects, like butterflies, can see red.

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Insects - Reproduction

• Sexes are separate, some are parthenogenetic.
• Fertilization is internal.
• In some, like butterflies, nutrients are passed
  to the female as well as sperm.

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Insects - Reproduction

• Insects have a variety of methods for attracting
  mates.
• Pheremones play an important role in many
  species.
• Fireflies communicate using light flashes.
• Crickets communicate using sound.

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Insects - Reproduction

• Female insects deposit eggs on a specific habitat
  that will provide food for larvae.
• Monarch butterflies lay eggs on milkweed plants.
• Parasitoid wasp species lay eggs on tomato
  hornworms.
• Mosquitoes lay eggs in standing water where the
  larvae will live as filter feeders.

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Insects - Metamorphosis

• Many insects undergo metamorphosis during their
  development.
• Each stage between molts is called an instar.

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Insects - Metamorphosis

• Insects with complete metamorphosis have larval
  stages specialized for eating and growing that
  are known by such names as maggot, grub, or
  caterpillar.
• The larval stage looks entirely different from
  the adult stage.

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Insects - Metamorphosis

• Female butterflies lay eggs on the plant that the
  caterpillars will feed on.
• After the eggs hatch, the larvae (caterpillars)
  eat and grow, molting many times.
• When it reaches a certain size, the larva will
  molt one more time, becoming a pupa (chrysalis
  in butterflies).

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Insects - Metamorphosis

• Metamorphosis from the larval stage to the adult
  stage occurs during a pupal stage.

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Insects - Metamorphosis

• In incomplete metamorphosis, the young, called
  nymphs resemble adults but are smaller and go
  through a series of molts until they reach full
  size.

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Diapause

• Insects are able to undergo dormancy during harsh
  conditions.
• Hibernation winter dormancy
• Estivation summer dormancy
• Diapause arrested growth that occurs regardless
  of conditions.

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Defense

• Aposematic coloration many insects utilize
  bright colors as a warning that they are toxic.

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Defense

• Batesian mimicry when a palatable species
  mimics the bright colors of an unpalatable
  species.
• Müllerian mimicry when two unpalatable species
  have come to resemble each other.

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Defense

• Cryptic coloration often insects are colored
  and patterned very much like the plants they are
  found on, making them very difficult to see.

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Defense

• Other defensive features include the exoskeleton,
  offensive odor (as with the stink bug), bites and
  stings.

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Insect Behavior

• Insects exhibit a wide range of behaviors
  involving innate behaviors, pheromones, and
  learning.

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Insect Behavior

• Fireflies use bioluminescence to signal each
  other. The female firefly attracts males by
  using a particular flash pattern.
• Another firefly species mimics the call of the
  female and then eats the males that arrive.

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Social Insects

• Honey bees, ants and termites have complex social
  groups.
• In honeybees
• The queen is the reproductive female.
• Workers are non-reproductive females.
• Drones are haploid males.

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Social Insects

• Ants have fascinating societies where they farm
  fungi, herd ant cows (aphids which they keep
  for the honeydew that they secrete), sew their
  nests with silk, and even use tools.

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Insects and Humans

• Insects can be harmful, spreading disease, eating
  crops etc.
• Care must be taken when controlling pests that
  beneficial insects are not harmed.

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Insects and Humans

• Or they can be beneficial, preying on harmful
  insects, fertilizing crops etc.

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Phylogeny

• Terrestrial insects first appeared in the
  Devonian period (408 mya).
• Several orders of winged insects were present by
  the Carboniferous (360 mya).
• Relationship between myriapods and insects is
  debated.