BIOLOGY

INSECTS

Concepts/Ideas/Facts:

1. most successful group of animals in terms of both diversity and numbers
2. insects pollinate more than 2/3 of the world’s flowering plants

Definitions:

1. Metamorphosis – the distinct changes through which an immature organism passes into adulthood.  Metamorphosis enhances survival because different developmental stages of the insect fulfill different functions.  This eliminates conflict between two activities that require great amounts of energy – growing and reproduction.  It eliminates competition between larvae and adults for food and space.  It also helps insects survive harsh weather, the insect spending winter encased as a pupae.
2. Incomplete Metamorphosis – the nymph resembles the adult form
1. Egg – first stage of insect life
2. Nymph – immature, smaller form of the organism that looks somewhat like the adult but has underdeveloped reproductive organs, and lacks wings
3. Adult – mature organism
3. Complete Metamorphosis – neither larva nor pupa resemble the adult
1. Egg – first stage of insect life
2. Larva – second stage or caterpillar stage of complete metamorphosis where the organism doesn’t resemble the adult at all.
3. Pupa – transition, immobile stage of metamorphosis where a hard outer covering (cocoon) forms encasing the pupa so it can undergo the physiological changes into an adult
4. Adult – mature adult
5. Cocoon – hard, protective outer covering of a pupa of a moth
6. Chrysalis – hard, protective outer covering of a pupa of a butterfly
4. Ootheca – a batch of eggs is cemented together to form an egg packet
5. Chorion – eggshell
6. Pheromone – chemical released by an animal that affects the behavior or development of other animals of the same species.
7. Parthenogenesis – reproduction without males, the eggs are unfertilized but develop and hatch into nymphs or larvae that are always female themselves.
8. Entomology – the study of insects
9. Entomologist – scientist who studies insects

Characteristics of Insects:

1. exoskeleton
2. jointed appendages
3. segmented body
4. body has three parts: head, thorax, and abdomen
5. head has one pair of antennae
6. thorax has three pairs of jointed legs
7. some species have one or two pair of wings
8. abdomen divided into 11 segments and no wings or legs are attached to it.
9. Sex organs located in abdomen

Categories of Variation:

1. Structural Variations – differences in morphology, how something is physically constructed
2. Physiological Variations – differences in the way internal systems work
3. Behavioral Variations – the differences in the ways organisms respond to their environment

Success of Insects

1. rapid reproduction due to short life span which exacerbates natural selection
2. exoskeleton
3. ability to fly
4. small size allows for several species to inhabit different environments within a small area without competing with one another.
5. complete metamorphosis allows for different developmental stages of the insect to fulfill different functions which eliminates conflicts between two activities that require great amounts of energy – growing and reproduction.  It eliminates competition between larvae and adults for food and space

Definitions:

Structure of Insects: Three Sections

1. Head – anterior segment which contains the brain and most of the sensory organs such as the antennae and compound eyes.  Also contains complex mouth parts.

1. Labium – liplike structure that hold food in position for tearing or chewing
2. Labrum – structure forming the roof of the mouth in insects
3. Mandibles – rough-edged jaws which tear off bits of food
4. Maxillae – second set of jaws behind the mandibles which further hold and cut food
5. Salivary Glands – produce digestive juices
6. Antennae – touch and smell sense organ on the head
7. Nerve Ganglia – bundle of nerves in the head that acts as the insect’s brain

2. Thorax – middle segment where the legs and wings are attached
1. Prothorax – has one pair of walking legs
2. Mesothorax – has one pair of walking legs and also attached forewings
3. Metathorax – has either one pair of legs or sometimes one pair of jumping legs and also attached hindwings
3. Abdomen – posterior segment which is specialized for reproduction and has structures for digestion, respiration, and excretion.

a.      Tympanum – small, nerve-rich cavity covered with a sound sensing membrane located along the first abdominal segment

b.      Ovipositors – pointed organs for depositing eggs into the soil

4. Tarsus – foot
5. Hind Wings – used for flight
6. Forewings – leathery wings that protect the hindwings
7. Esophagus – tube that goes from the mouth to the crop and passes food to the digestive system
8. Crop – after the esophagus, it temporarily stores food
9. Gizzard -  food passes from the drop to the gizzard where sharp chitinous plates shred it
10. Midgut or Stomach – shredded food from the gizzard is digested
11. Gastric Cecas – stomach pockets that secrete digestive enzymes
12. Coelom – body cavity where nutrition substances are transferred to the circulatory system
13. Hindgut – made up of the colon and rectum, it is where undigested food and waste go from the midgut
14. Malpighian Tubules – tubules in the midgut which remove chemical waste from the blood and deposit it in the rectum
15. Anus – portal for the removal of waste to the outside environment
16. Aorta – a large blood vessel in insects.  Muscles in the posterior regions of the aorta pump blood forward into the coelom where nutrients are picked-up for transport to organs and cells.  The blood also carries cellular waste to the malpighian tubules completing the circuit back to the aorta through pores called ostia.
17. Ostia – pores in the malpighian tubules through which waste flows
18. Spiracles – tiny openings in the abdomen and thorax of insects through which air flows
19. Trachea – air tubes that allows air to flow from the spiracles directly into body tissue.  Waste gases which have diffused out of cells is collected in the trachea and expelled through he spiracles.

Insect Defense Mechanisms:

1. aggressive defenses – poisonous sprays
2. stings
3. Camouflage – ability to blend into surroundings
4. Warning Coloration – bold, bright, color patterns that mark them clearly recognizable and warn predators away
5. Mullerian Mimicry – similar patterns developed between poisonous species and non-poisonous species, encouraging predators to avoid all similar colored species.
6. Batesian Mimicry – similar colorations and structures between unpalatable species and palatable species, encouraging predators to avoid all similar colored and structured species.

Hormonal Control of Metamorphosis

1. brain hormone – stimulates a gland in the thorax to release molting hormone
2. molting hormone (ecdysone) – in connection with high juvenile hormone it causes larva to molt
3. juvenile hormone – a decrease of this hormone causes the larva to change to a pupa.  The absence of juvenile hormone starts the change from pupa to adult

Insect Behavior

Bees:

1.   Division of Labor

1. Worker Bees – sterile females that make up the vast majority of bees.  They do all the work except reproduction and live about 6 weeks.  At first they are called nurse bees and they feed honey and pollen to the queen, drones, and larvae.  They produce royal jelly.  After about a week they stop producing royal jelly and produce wax for building and repair of the honeycomb.  They also clean and guard the hive, and circulate air by fanning their wings.  The worker bees spend the last week of the lives collecting pollen and nectar
2. Queen – only fertile female in the hive whose only purpose is to reproduce.  She may produce up to a million eggs per year and lives about 5 years.  The queen secretes a substance called queen factor that prevents other females larvae from becoming sexually mature.
3. Drones – male bees developed from unfertilized eggs, drones are only used in mating, their mouthparts are too short for to obtain nectar so they must be fed by worker bees.  A hive only contains a few hundred drones which are killed when honey supply dwindles.

3. Instinct – genetically controlled or innate behavior
4. Division of Labor – different kinds of adult individuals that are specialized in form and function.

Great Insect Anatomy Website

http://www.earthlife.net/insects/anatomy.html