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