Insects

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Insects (Phylum Arthropoda Sub-Phylum Uniramia)

• Evolved over 300 million years ago
• Most successful group of animals (700,000 to 10
  million species)

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• Diversity (species and variety)
• Numbers (population size)
• Success due in part to enormous range of
  variation
• Structural (morphological)
• Physiological (chemical)
• Behavioral

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Characteristics and Classification

• Body - 3 parts
• Head with 1 pair of antennae
• Thorax with 3 pair of jointed legs and in many
  species 1-2 pair of wings
• Abdomen with 11 segments (lacks wings and legs)

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Success of the

• Found virtually everywhere except the deep ocean
• Extremely short life span -gt rapid adaptation to
  new environments
• Small size -gt greater partitioning of habitats
  while minimizing competition
• Flight -gt greater dispersal, escape from
  predation, and movement into environments less
  accessible to other species

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Insects and Human Society

• Positive impact
• Major pollinator of flowering plants (2/3 of all
  plants)
• Food for fish, birds and mammals (important link
  in food web)
• Help recycle materials (termites)
• Useful biproducts (honey and silk)

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• Negative impact
• Agricultural pests
• Spread disease

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Grasshoppers

• 3 main body segments
• Head (brain and sense organs)
• Antennae
• Compound and simple eyes
• Complex moth parts

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• Thorax (legs and wings attached)
• Prothorax and mesothorax (each have pair of
  walking legs)
• Metathorax (jumping legs

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• Abdomen (organs of reproduction, digestion,
  respiration, and excretion)
• 2 pair of wings
• Leathery protective forewing (mesothorax)
• Hind wing which is used for flight (metathorax)

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Digestive System

• Specialized mouthparts (liplike labium and
  labrum, jawlike mandibles and maxillae)
• Salivary glands (produce saliva)
• Digestive ceca (produces digestive enzymes)

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• Food -gt mouth -gt esophagus -gt crop (storage) -gt
  gizzard (chitinous plates shred it) -gt stomach
  (mid gut) (mixes with gastric enzymes from ceca
  and absorbed) -gt hind gut (colon and rectum) -gt
  anus

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Excretory System

• Malpighian tubules in hindgut remove wastes from
  blood and deposit them in the rectum

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Circulatory System

• Open circulatory system
• Blood -gt aorta -gt hearts (muscular region of
  aorta in posterior abdomen) -gt anterior coelom
  (head) -gt abdomen (absorbs and disperses
  nutrients) -gt aorta via ostia

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Respiratory System

• Air -gt spiracles (opening in thorax and abdomen)
  -gt tracheae (network of air tubes) -gt body
  tissues
• Contraction of abdomen reverses process

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Nervous System

• Simple brain
• Ventral nerve cord
• 3 simple eyes (detect light)
• 2 compound eyes (composed of hexagonal lenses
  capable of detecting movement but not sharp
  images)

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• Tympanum (detects sounds located on first
  abdominal segment)
• Antennae (detects touch and smell)

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Reproductive System

• Sperm deposited into female's seminal receptacle
  (stored until eggs are released)
• Eggs fertilized internally
• Ovipositor (pair of pointed organs at tip of
  abdomen) used to dig a hole in soil and deposit
  eggs

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Development

• Metamorphosis - developmental changes -gt distinct
  changes in form and size
• Incomplete Metamorphosis
• 3 stages (egg, nymph, and adult)
• Nymph- smaller immature form similar to adult
  but underdeveloped reproductive organs and lack
  wings
• Examples are grasshoppers and termites

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• Complete Metamorphosis
• 4 stages (egg, larva, pupa, and adult)
• Examples are butterflies, beetles and most other
  insects

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Hormonal Control

• Controlled by sequential expression of genes
• Interaction of 3 hormones (brain, molting and
  juvenile)

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• Brain hormone stimulates release of molting
  hormone (effect depends on level of juvenile
  hormone)
• Juvenile hormone level high -gt molting hormone -gt
  larva molts
• Juvenile hormone level decreases -gt molting
  hormone -gt larva develop into pupa
• Juvenile hormone absent -gt molting hormone -gt
  pupa develops into adult

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Importance of Metamorphism

• Different developmental stages -gt different
  functions (specializations)
• Eliminates energy conflicts between growth and
  reproduction
• Eliminates competition between life stages
• Multistage life cycle helps survive harsh weather

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Defense

• Defensive adaptations (agressive and passive) -gt
  enhanced survival
• Camouflage (cryptic coloration)
• Warning coloration
• Mullerian mimicry- poisonous or dangerous species
  having similar patterns of coloration

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• Batesian mimicry- nonpoisonous or nondangerous
  species having similar pattern or color to a
  poisonous or dangerous unrelated species

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Insect Behavior

• Social behavior in honeybees
• Behaviors are genetically determined (instinctual
  or innate)
• Division of labor -gtcomplex societies -gt
  interdependence and need for communication

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• Hive consists of 3 distinct forms
• Workers - sterile females majority of
  individuals in hive
• Queen - fertile female only function is
  reproduction
• Drones - male bees only function is

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Workers

• Average life span approximately 6 weeks
• Perform many functions at different times during
  their lives
• 1st stage - feed honey and pollen to queen,
  drones and larvae (nurse bees) secrete royal
  jelly (high protein diet)
• 2nd stage - Stop producing royal jelly and begin
  secreting wax -gt build and repair hive, guard
  hive and fan wings to circulate fresh air in hive

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• 3rd stage - gather nector and pollen legs
  modified with special structures to collect
  pollen ovipositor modified for defense (stinger)

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Queen and Drones

• Queen identical to workers except continuously
  supplied with royal jelly Queen secretes "queen
  factor" which prevents other female larvae from
  becoming sexually mature
• Mates only once sperm stored in seminal
  receptacle for up to 5 years or more

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• Drones (haploid (n) males) develop from
  unfertilized eggs sole function to deliver sperm
  to queen must be feed by workers

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Communication

• Pheromones - chemicals released by an animal that
  affects the behavior or development of other
  animals of the same species
• Sounds
• Tapping, rubbing, or signaling

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Honey Bee communication

• Round dance - food source near but no indication
  of exact location
• Waggle dance- food far from hive, dirction of
  food indicated by the angle of the straight run
  and the distance indicated by the duration and
  the number of waggles