BI207-- insect structure and function

examples of insects with sponging mouthparts

housefly

horsefly— cuts and sponges

sucking (coiled) mouthparts

• adult lepidoptera(e.g. butterflies and moths) and some flies

• long tongued flies

• sucking up liquids using suctorial mouthparts

• proboscis or rostrum

• some modified for biting and sucking

• butterfly proboscis used for sucking nectar

piercing/ sucking mouthparts

• blood sucking flies

• variety of skin penetration and feeding mechanisms

• horse flies and black flies— labium forms non piercing sheath for other mouthparts

• other piercing and sucking— Hemiptera (true bugs), thysanoptera (thrips), siphonaptera (fleas) and sucking lice

• different mouthpart components form needle like stylets capable of piercing plant or animal tissue

• e.g. aphids

• filter feeding

• larval mosquitos, caddisflies— get food from filtering particles in water (bacteria, algae, detritus)

some factors contributing to success of insects

• cuticle

• flight

• reproductive potential (many offspring)

• adaptability (e.g. same structure, different functions)

• small size (can colonise many habitats)

thorax

• prothorax, mesothorax, metathorax

• wings on 2nd and 3rd segments

• legs- on pair per segment

• spiracles for gas exchange

• wings and legs for locomotion

wings and flight

• present in most insects

• contribute to their success— disperse, colonise new habitats, escape enemies/ poor conditions

• fully developed only in adult

• 1 pair more primitive

• flap like— supported by tubular veins

• fore and hind wings can be coupled together (e.g. hooks)

• small insects— wing area often expanded [ aerodynamic challengers]

structure of wings

thin flat structures

double layer of cuticle strengthened by ‘veins’

Veins:

• cuticle is heavily sclerotised

• contain a blood space, a trachea and often a nerve

• provide a strengthening framework

• net like in more primitive insects (locust)

• evolutionary tendency towards the union of vein branches, giving stronger support ( hymenopterans[bee])

• two pairs linked e.g. Hymenoptera (bees); effectively forming one pair

wing folding

early insects held wings outstretched

later evolution of sclerites in wing base allowed folding- hence exploitation of more habitats

• variations to basic paln of two pairs of similar wings include

• - first pair hardened, protective (elytra)— e.g. coleoptera

• - second pair reduced to halteres, knobs that aid balance during flight e.g. diptera (fly) (daddy long legs)

• - both pairs lost (e.g. lice, fleas), an adaptation to the ectoparasitic lifestyle

• colourful— camouflage, display (e.g. order lepidoptera [butterflies and moths])

what does flight require

• highly developed nervous and sensory system for navigation and coordination

• efficient fuel and oxygen supply for intense metabolic activity (costly)

• the wings and the muscles that move them

tracheal system

• air sacs help to provide extra oxygen especially to flight muscles during active flight

• gasses pass through the system by diffsuion, aided by body movements in larger insects

legs

• adults and nymphs

• segmented fore, mid and hind legs

• adults= thoracic legs, abdominal legs only some larvae

• consists of a series of cylinders linked by articular membranes

abdomen

• segmented (primitively 11, segment 1 may be reduced)

• aquatic larvae gills along abdomen

internal anatomy (dont need to know about it in detail)

• nervous systems

• digestive system

• respiratory system

• circulatory system

• endocrine system

• reproductive system

moulting

• rigid exoskeleton— growth by means of a gradual increase in external body size is not possible

• solution= periodic shedding of the cuticle in a process called moulting or ecdysis

• new cuticle forms under the old one; much of the old cuticle is reabsorbed and re-used, and the remainder is cast off

• shed cuticle (exuvium) includes the linings of gut and trachea

  • primitively wingless insects (apterygota)— moulting occurs throughout life

  • most insects— fixed number of moults, sexual maturity reached after last moult

  • trigged by hormone ecdysone

dangers of moulting

• new cuticle is soft

• animal vulnerbale to injury, predation, osmotic stress

• newly moulted insect is vulnerable until cuticle hardens

• often hides

stages of moulting cycle

premoult— when tissues fill the cuticle, prepares physiologically for moult; epidermis separates form the cuticle (apolysis)

intermoult— growth, no increase in external body size

moult

new cuticle

• soft

• expanded by taking in air on water

• hardened by sclerotization

• extra air or water is expelled, leaving room for growth between moults

postembryonic devleopment

primitively wingless insects— simple devleopment

winged insects

• incomplete metamorphosis/ direct devleopment (hemimetabolous)

• complete metamorphosis/ indirect development (holometabolous)

primitively wingless (apterygota)— simple devleopment

• no metamorphosis: young resemble the adults in every respect except sexual maturity

• moulting continues until death

winged insects— incomplete metamorphosis or direct development

• young usually look like miniature, wingless adults

• wing buds clearly visible externally (hence the term exopterygote)

• at final ecdysis, wings assume full size

• wings appear at last moult

• adults differ from young in possession of wings and sexual maturity

• young (nymphs) may live similar lives to adults— except where nympphs are aquatic and adults terrestrial e.g. mayflies

winged insects- -complete metamorphosis or indirect development

• more highly evolved

• larvae differ from adults

• pupa— externally inactive, but internally, tissues are rearranged into those of adult

• wings develop under larval cuticle (hence endopterygote)— not visible until late in pupal stage

• total restructuring of body takes place during pupal stage

• larvae can exploit different resources to adult

• some pupae nakey snakey— some protected

• four most successful orders have completed metamorphosis

Hormonal control of devleopment

ecdysone

• secreted by prothoracic gland

• triggers moulting

Juvenile hormone

• secreted by corpora allata

• prevents metamorphosis

• high until last larval moult

• drop before pupation

• drop further during pupal stage, causing insect to become adult