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What are the characteristics of an arthropod?
An insect is an arthropod
- Segmented body
- Paired jointed appendages (specialized)
- Exoskeleton of chitin
- Metamorphosis and molting
- Protective colouration and resemblances
- Cephalization and specialization of body segments (tagmosis)
Name the major living arthropod groups.
What are the characteristics of Crustacea?
>67, 800 described species
crabs, lobsters, shrimp, krill, isopods, barnacles, amphipods, ostracods, branchiopods
Marine and freshwater environments
Biramous appendages – seven segments
Two pair of antennae- one pair uniramous
All have a first larval stage called a nauplius
What are the characteristics of Chelicertata?
Centipedes, millipedes, pauropodans, symphylans
Single pair of antennae
Paired uniramous appendages
What are the characteristics of Myriapoda?
- Centipedes, millipedes, pauropodans, symphylans
- All terrestrial
- Single pair of antennae
- Paired uniramous appendages
What are characteristics of Hexapoda?
Most diverse group of organisms on the planet ca 1,000,000 species and counting
- Entognatha (diplurans, proturans, collembola)
- Ectognatha (insecta)
- Six legs (3 pairs)
Body composed of 19 true somites + acron
- Three major body segments: head (acron + 5 somites), thorax (3 somites), and abdomen (11 somites)
- External mouthparts:
- Three pairs of legs (adults)
- One pair of antennae (adults)
- Compound eyes and ocelli (adults)
- Usually two pair of wings (adults only)
- Spiracles and trachea
How have insects and humans interacted positively and negatively through time?
- Crop damage and losses (broadacre, horticultural, forestry)
- Aesthetic injury (crops and ornamentals)
- Stored product losses
- Structural pests
- Destruction of possessions (furniture, clothing, carpet, insect collections)
- Animal health
- Human health (300 million cases of acute malaria/ yr)
- Extinction/biodiversity impacts
- Experimental animals – Drosophila melanogaster
- Scientific models for ecology, robotics, physiology etc.
- Bioindicators – environmental monitoring, forensics
- Medical tools
- Insects as food
- Insect products
- Religious icon
- Art, music, poetry
Why are insects regarded as the most successful group of organisms on the plant?
- Reproductive capacity
- SizeNumber of known species
- Estimates of species diversity
- Habitats occupied
describe the function of the exoskeleton.
Name the layers of the exoskeleton
Describe the structure of the cuticle.
- Calcium carbonate
- Internally- trachea, fore and hindgut
What is sclerotization?
hardening of the exoskeleton
- Phenolic bridges
- 20 segments (19 + acron)
- 6 fused to form head
- 3 thoracic
- 11 abdominal
- Sternites (ventral)
- Tergites (dorsal)
- Pleurite (lateral)
Key features of the insect head.
Key features for the thorax?
- Wings only on 2nd and 3rd
- Tergal plates called nota, notum
- Pronotum usually large in beetles, grasshoppers, cockroach, ect
- When metathorax and misothorax bonded close together called Pterothorax
Key features of the abdomen?
- copulatory opening
- apodemes- attachment sites for muscles
- ovipore-pore like sexual organ of female
- Terminal segments-cerci, ovipositor, terminal filaments
explain chewing mouthparts and their function
- labrum- upper lip
- mandables- grasping and grinding of food
- Maxilla- sensory and palps help in holding food
- Labium- Sensory lower lip (Modified)
- Rasping sucking
- Filter feeding
Name the segments of insect antennae
- 1st segment-Scape
Name and describe types of antennae
Name the segments of insect leg
Functions of legs
- Walking (gressorial)
- Running (cursorial)
- jumping (saltatorial)
- swimming (natatorial)
- digging (fossorial)
- Seizing prey (raptorial)
describe the legs of the immature insect
- prolegs on the abdomen are usully lobe like
- have hooks called crochets
- prolegs on thorax same number as adult have hooks
describe four types of wings
Name 4 insects without wings, orders too.
- Ants Hymenoptera
- Termites Isoptera (sometimes)
- Fleas siphonaptera
- Silverfish Thysanoptera
describe the difference between direct and indirect flight mechanisms
direct flight uses muscles that are connected to the wings, older groups orthoptera,blattadea.
Indirect uses the deforming of the thoractic box through muscle action.
describe the structure of the hemocoel
A hemocoel (or haemocoel) is a series of spaces between the organs of organisms with open circulatory systems. A combination of blood, lymph, and interstitial fluid called hemolymph circulates through the hemocoel.
Blood containing body cavity
- Divided by dorsal diaphragm and ventral diaphragm
- Pericardial hemocoel
- Perivisceral hemocoel
- Perineural hemocoel
describe the composition and function of hemolymph
- all chemical exchanges between insect tissues are mediated by hemolymph
- ie. transport of hormones
wastes are removed to excetory regions.
low oxygen carrying capacity
serves as a water reserve
pressure changes important in molting and ventalation
clear colorless but may be yellow, green or blue
how does hemolymph circulate throughout the insect body
a system of muscular pumps move blood through compartments separated by membranes.
anterior part of main pump aorta and posterior is heart
openings called ostia take up hemolymph
describe the fat body and its role
Conspicuous white or yellow tissue
- Equivalent to the vertebrate liver
- Metabolism of carbohydrates, lipids and proteins
- Energy storage – glycogen, fat and protein
- Regulation of sugar levels
- Manufacture of hemolymph proteins
- Adipocytes - fats
- Urocytes -
- Mycetocytes (bacteria-like symbionts)
describe insect gas exchange
- Internal air-filled tracheae
- Contact all internal organs and tissues
- More numerous in tissues with high O2 demand
Tracheae open to the outside through small holes called spiracles. In the grasshopper, the first and third segments of the thorax have a spiracle on each side. Another 8 pairs of spiracles are arranged in a line on either side of the abdomen.Spiracles open into large tracheal tubes. These, in turn, lead to ever-finer branches. The branches penetrate to every part of the body. At their extreme ends, called tracheoles, they may be less than 1 µm in diameter, and are probably filled with liquid. Every cell in the insect's body is adjacent, or very close to, the end of a tracheole.
Identify the three regions of the gut and escribe the general functions of each
- Fore gut -lined with cuticle,
- The fore gut is generally considered to consist of four sections, the Pharynx, the Oesophagus, the Crop and the Proventriculus. It is also known as the Stomodaeum.
- The pharynx is the first part of the fore gut and apart from being a tube that connects the interior of the mouth area (sometimes known as the 'Buccal Cavity) with the more inward parts of the gut it sometimes serves as a pump to suck up the liquefied food of those insects which feed by means external digestion. The Oesophagus is basically a tube leading to the mid gut via the crop and the proventriculus or gizzard. The crop is simply a storage area and the proventriculus, or gizzard, is a muscular extension of the crop. In those insects which feed on solid foods it is used to grind the food up into smaller particles, it can also serve as a filter to keep oversized particles out of the main digestive tract and as a valve controlling the flow of food into the midgut. The fore gut and the mid gut are separated by the 'stomodeal or cardiac valve'.
Mid gut- The midgut (called the Mesenteron in some books) runs from the 'digestive or gastric caeca', a series of stubby pointed tubes leading off from the stomach to just before the Malpighian tubules, a series of long thin tubes which absorbs solutes, water, and wastes from the surrounding hemolymph. The wastes then are released from the organism in the form of solid nitrogenous compounds. . In between the two of these is the stomach, or ventriculus, which is the area of most active digestion. The gastric caeca serve to increase the surface area of the midgut, thus increasing both its ability to secrete digestive enzymes and its ability to extract useful products from the partially digested food. The useful proteins, vitamins and fats that are released by the digestive processes pass across the wall of the midgut into the body cavity. The mid gut is lined by a semipermeable membrane composed of protein and chitin, like the cuticle, which allows the passage of liquids and dissolved substances to the midgut wall while preventing the passage of solid food particles, it is continually worn away by the passage of food through the gut and replaced by the epithelial cells of the mid gut wall. The mid gut and the hindgut are separated by the 'proctodeal valve'.
- Hind gut- lined with cuticleFrom the mid gut food passes to the hind gut. The hind gut comprises the 'intestines' which is where much of the diffusion into the the insects body occurs. The 'rectum' which compresses the undigested food and waste products, extracts more water from this if necessary before it is passed out through the 'anus' as faeces.
- Arising from and the foremost part of the hind gut are the Malpighian tubules are not really to do with digestion at all but with elimination. They act like our kidneys and extract metabolic waste products from the circulating body fluid called the haemolymph and excrete them into the intestines which is the first part of the hind gut.
- Though insects possess a large number of digestive enzymes, they are often helped by the presence of symbiotic micro-organisms, such as protozoa in the case of the termites and some primitive cockroaches which feed on wood, and bacteria
Describe the major sections of the insect central nervious system.
subesophageal ganglion-composed of three pairs of fused ganglia. It controls the mouthparts, the salivary glands and certain muscles. The subesophageal ganglion sits beneath the esophagus.
ventral nerve cord-Ventral nerve cords from anterior to posterior (the thoracic and abdominal tagma in the arthropods) are made up of segmented ganglia that are connected by a tract of nerve fibers passing from one side to the other of the nerve cord called commissures
Identify the main organs of the male insect reproduction
Externally the sexual organs of the male, also called genitalia, consist of a pair of 'claspers' which the male uses to hold onto the females genitalia and an intromittant organ called the 'aedeagus' which is the means by which the male passes the sperm onto the female.
Internally the male reproductive organs consist of a pair of 'testes' containing the 'testicular follicles' where the spermatozoa are made, the 'vas deferens' which is the tube down which the sperm travels, a 'seminal vesicle' which is where the sperm is stored prior to mating, and accessory glands which supply seminal fluid for additional volume and to nourish the sperm before and during their journey.
Identify the major organs in female reproduction.
Externally the sexual organs, called genitalia, of a female insect generally consist of an 'ovipositor' which is often encased in a pair of filaments called a 'sheath' and is which is used to by the female to put her eggs where she wants. Its form very greatly throughout the Insecta (i.e. the whole order of insects). The ovipositor of the Diptera (True Flies) is functionally similar i.e. it is used to lay eggs, but is morphologically distinct i.e. it arises or is made from different parts of the insects anatomy and should be called a 'pseudovipositor'. The median part of the oviduct which receives the aedeagus during mating is called the 'vagina'.
Internally the female reproductive organs consist of a pair of ovaries which contain the ovarioles which is where the eggs or ova are formed, the bursa copulatrix which is where the sperm is first received )in those insects which have it) and a spermatheca which is where the sperm is stored. There are also various tubes down which the ova travel on their way from the ovaries to the outside world, fertilisation occurs in the common oviduct after the the egg has received its shell or the 'chorion'. To facilitate this the shell contains a very small opening at one end called the micropyle which allows the sperm to enter. As well as tubes there are several important glands some of which (spermathecal glands) allow the female to keep the sperm alive and viable for a long time, as much as 20 years in some social insects (Ants and Bees); and some of which (collaterial glands) secrete the substances which allow the female to stick the eggs where she wants then to stay i.e. underneath a leaf, or to protect the eggs as in the ootheca produced by the Cockroaches and Mantids
describe the structure of a photoreceptor
cells containing light sensitive molecules.
The phtoreceptive structure is called the rhabdom, which is comprised of several adjacent retinula (or nerve cells)
Light changes the configuration of the visual pigment, triggering a change in electrical potential across the cell membrane. This stimulates the chemical signals to the brain.
describe the structure of a chemoreceptor
- Olfactory receptor neurons
- Antennae; palps; genitalia
- Gustatory receptor neurons
- Mouthparts, legs and ovipositor also antennae
- Sugar, water or salt concentrations
- Sensilla for taste and smell appear similar in structure but differ in the number of pores; taste fewer than smell
Describe the structure of mechanoreceptors
- Tactile sensation
- Trichogen cell-grows the hair
- Tormogen cell – grows the socket/support
- Nerve cell – produces a dendrite and axon for detection and transmission
- Body touching
- Gravi ty Sound/air vibrations