Insects
Chapter 37
The Insect World
Section 37.1
Characteristics of InsectsThree tagmata:
1.Head: mandibles to chew, pair of antennae for sensory
2.Thorax: 3 pairs of jointed legs, most have 1 or 2 pairs of wings
3.Abdomen: 9-11 segments
Head Thorax Abdomen
Exoskeleton with…
Antennae Examples: Leg Examples:
Appendage examples:
Two types of mouthparts:
• The study of insects– & other terrestrial arthropods
• Person = entomologist– Classify insects into 25 orders based up:
• Mouthparts• Number of wings• Type of development
Entomology:
Classification of Insects• Subphylum: Hexapoda• Class: Insecta• Common Orders:
– Hemiptera– Homoptera– Isoptera– Odonata– Orthoptera– Coleoptera– Diptera– Hymenoptera– Lepidoptera
Table on page 743
Success of Insects
• Insects live everywhere (except deep ocean)
• 1 million species (more than 3x all other animals!)– 10 million might exist
• Why so many? – Ability to fly
• Escape & dispersal
– Small– Short life spans
• Quick adaptations
Insects and People
• Competition for food • Spread diseases
– Plague, typhoid fever, malaria
• Consume clothing & carpet • Crop pollination • Make commercial products
– Wax, silk, honey
• Recycle nutrients
Insect Development
• Hatchling must go through several molts to reach adulthood (sexual maturity)
• Metamorphosis: major developmental changes from larvae to adult
• Two forms: incomplete & complete
Incomplete Metamorphosis
• Nymph: immature form of insect that looks like adult
• Only the adult can fly and is sexually mature
Complete Metamorphosis
• Two stages of development that look drastically different
• Pupa: changing from larvae to adult
• Cocoon: protective covering of pupa
• Chrysalis: butterfly pupa protection
Insect Defense
• Passive defense examples:– Camouflage– Look like plants
• Aggressive defense examples:– Venomous stingers– Harmful chemicals
• Warning coloration: color pattern to warn of poison
Mimicry
• Mullerian mimicry: poisonous species mimics the coloration of another poisonous species– Bees & wasps
• Batesian mimicry: harmless species mimics the coloration of a poisonous species– Monarch & viceroy butterflies
Grasshoppers
Subphylum Hexapoda
External Structures:
• Head = mouthparts, antennae, simple & compound eyes
• Thorax = 3 parts:– Prothorax = 1st pair walking legs– Mesothorax = 2nd pair walking legs &
forewings (protective)– Metathorax = 3rd pair legs (jumping) &
hindwings (flying)
• Abdomen = upper & lower plates connected by flexible exoskeleton– Covered by waxy cuticle (prevents
desiccation)
Feeding• Chewing mouthparts (feed on plants)
– Labrum: functions like upper lip– Labium: functions like lower lip– Mandible: tears food– Maxilla: helps hold & cut food
Digestive Tract
• Mouth saliva (from salivary glands) esophagus crop (storage) gizzard midgut/stomach (bathed in enzymes from gastic ceca) nutrients absorbed in hindgut/intestine anus
Circulation, Respiration, & Excretion
• Circulatory system:– Open– Aorta (large, dorsal vessel)– Heart (pumping organ)
• Respiratory system:– Tracheae (site of air diffusion inside body)– Spiracles (openings to allow air in/out)
• Excretory system:– Malpighian tubules: return most water back
to hemolymph, rest leaves body via feces
Neural Control
• CNS = brain, ventral nerve cord, & ganglia at each segment
• Antennae – touch & smell
• 3 simple eyes – intensity of light
• 2 compound eyes – sight
• Tympanum – sound & communication
• Sensory hairs - touch
Reproduction
• Separate sexes (male & female)
• Sexual Reproduction:1. male deposits sperm into female
seminal receptacles
2. Eggs released from ovaries
3. Internal fertilization
4. Ovipositor: digs a hole in soil to lay eggs
Insect Behavior
Section 37.2
Communication
• Chemical communication via pheromones– Chemical released that affects behavior
or development of other members of same species
• Uses of pheromones:– Attract mates– Identify hives– Food trails
video
Communication Con’t…
• Sound communication via chirping, buzzing, etc. (crickets, mosquitoes)– Attract females– Protect territories
• Sight communication via flashes of light (fireflies)– Find mates
Behavior in Honeybees
• Social insects: insects that live in colonies with division of labor
• Innate behaviors: genetically determined– Not taught or learned
• Three types of honeybees:1. Worker2. Drone3. Queen
Worker Bees
• Sterile females
• First adult week: feed honey & pollen to queen, drones, & larvae– Royal jelly
• Next two weeks: secrete wax (build & repair honeycomb), remove wastes, guard hive, circulate air in hive
Continued…
• Last weeks of life: collect nectar & pollen
• Adaptations:– Barbed stingers for protection of hive– Mouthparts for lapping nectar– Legs with pollen packers, baskets, &
pollen combs
Drones
• Males developed from unfertilized eggs– Parthenogenesis
• Can travel from hive to hive
• Sole function: deliver sperm to queen– succeed in mating = death– penis and associated abdominal tissues
are ripped from the body at intercourse
Queen Bee
• Continuous diet of royal jelly as larvae = queen bee
• Secretes pheromone “queen factor” that prevents other females developing into queens
• Sole role: reproduction– Mates only once– Sperm remains inside her for 5+ years– Lays millions of eggs per year!
The Dances of the Bees
• Dancing performed by scout worker bees
• Round dance: told workers that food was nearby but not exact location
• Waggle dance: told workers that food was far away and told location
Altruistic Behavior
• Definition: aiding other individuals at one’s own risk or expense
• Kin selection: increasing the propagation of one’s own genes by helping closely related individuals reproduce
• Example: worker bee stinging = death