Insects

(Phylum Arthropoda; Sub-Phylum Uniramia)

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

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

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)

Success of the

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

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)

 Negative impact  Agricultural pests  Spread disease

Grasshoppers

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

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

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

Digestive System

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

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

Excretory System

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

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

Circulatory System

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

Respiratory 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)

Nervous System

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

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

Development

 Metamorphosis - developmental changes -> 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

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

Hormonal Control

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

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

Importance of Metamorphism

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

Defense

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

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

Insect Behavior

 Social behavior in honeybees  Behaviors are genetically determined (instinctual or innate)  Division of labor -> complex societies -> interdependence and need for communication

 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

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 -> build and repair hive, guard hive and fan wings to circulate fresh air in hive

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

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

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

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

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