AD Insects Flashcards
What are the functions of an insect’s mouth parts?
Gather / capture food or food source (prey).
• Convey the food to mouth
• Process the food
Break food into smaller pieces (solids)
Convey saliva to food for extra-oral digestion (solids &
liquids)
Gathering / capturing of food is undertaken by the legs in some insects. Which insects?
Mantids & adult dragonflies (prey), bees (pollen)
Mantids have Raptorial forelegs and bees have gathering legs
Describe an insect’s mouthparts
Labrum = upper lip Mandible = upper jaw Maxilla = lower jaw Labium = lower lip
Describe mandibles
Heavily sclerotised & often hardened by Zn or Mn.
Each often differentiated into incisor & molar regions.
Biting surface can have ‘teeth’ &/or cusps that
reflect diet
Why is the labrum technically not a mouth part?
it is nonappendicular in origin
Describe the maxillae
Maxillae bear palps (‘fingers’) for manipulating & testing
food
Describe the labium
Palps used to manipulate & test food. Labium bears the hypopharynx which delivers saliva onto food
Describe the mandibles in Ant-lions and lacewing larvae
Have grooved (hollowed out) mandibles.
Mandibles + maxillae pierce the prey, & inject saliva.
Prey tissues are digested before
being sucked up
Weevils have a
proboscis. BUT it is an extension
of the cranium, NOT of the mouthparts
The mouthparts are the ancestral type. What is a proboscis?
the tubular feeding and sucking organ
moths, butterflies, and mosquitoes can have it
What are the 3 basic mechanisms for feeding on liquid?
- ‘Sponging’ (also ‘slash and sponge’: e.g. horseflies)
- ‘Hairy tongue’ (lapping)
- ‘Drinking straw’ (sucking)
Describe the sponging mechanism
Higher Diptera e.g. blow-fly
Proboscis can be retracted into the head capsule
& everted when needed for feeding.
• Labium tip is produced to form retractable / eversible lips
(labellae).
• Labellar internal surfaces bear grooves pseudotracheal
canals).
• When feeding on dried sugary foods, each labellum is spread over food (e.g. dried honeydew or solidified
nectar).
• Saliva oozes out from grooves along the pseudotracheal canals.
• Dissolved food + saliva mixture
finally sucked back to main canal
in proboscis.
Describe the hairy tongue mechanism
Hymenoptera (wasps, bees & ants)
• Proboscis is used for feeding on nectar +/or
other sugar-rich liquids.
• ‘Tongue’, derived from fused labial glossae is
hairy, used to lap up liquid food, even in spp.
with a short proboscis.
• Hairs increase surface area of glossa & are
hydrophilic.
• Saliva arises from hypopharynx.
• Conducted via salivary canal to tip of glossa
in long-tongued spp. such as bees.
• Mechanism analogous to microfibre cloths.
Describe the drinking straw mechanism
Lepidoptera, Hemiptera, (Hymenoptera), some Diptera
Feeding on blood, nectar, fruit juices, pre-digested
materials (e.g. digested prey or honeydew deposits).
Liquid drawn to mouth through
a tube by: capillarity (right) (in some cases) suction
Proboscis tip can be modified for piercing prey, plant tissues, hosts
Sucking in Lepidoptera:
• Galeae of maxillae are zipped by circular hooks (ventrally)
+ plates (dorsally).
• No additional supporting structure.
• Uncoiling due to increased blood pressure.
• Coiling due to:
elasticity of the cuticle (loose coiling) AND
intrinsic musculature (tight coiling).
Sucking in Diptera, e.g. mosquitoes: Serrated tips to mandibles & maxillae. • Pierce host’s skin, damages capillaries, pool forms. • Hypopharynx conducts saliva. • Labrum conducts food. • Labium is supporting structure. Mosquitoes thrust with their legs to help penetration of hosts skin
Do all ‘sucking’ insects really suck?
Xylem-feeders such as froghoppers & cicadas:
• Xylem is under strong negative pressure, so insects
have massive cibarial pumps
• Phloem-feeders such as aphids & many
planthoppers:
• Phloem is under positive pressure – the insects have
no need to ‘suck’ – they simply ‘tap into’ the supply
A bumble bee can detect the electric fields of flowers via WHAT?
the deflections of many tiny mechanosensory filiform hairs on its head and body
Describe an arthropod’s exoskeleton
Epicuticle: thin waterproof layer of protein, lipoprotein,
lipids, waxes. No chitin. Wax layer main barrier against
water loss
Exocuticle: protein and alpha chitin together form a complex glycoprotein. sclerotized where strength and rigidity is required, not in articular membranes
Endocuticle: less protein, more chitin. Mineralised in crustaceans.
Gland cell: different types, secrete waxy epicuticle, enzymes that promote scleritisation.
Epidermis and duct
Describe the tracheal system
Trachea provide a vast extension of cuticular surface area to allow exchange of gases
Compromise between oxygen supply and water loss in terrestrial insects.
Spiracles with closing valves.
Note circulatory system contributes only marginally to gas exchange.
Rather, tracheal system extensively branches in musculature and other tissues to supply
O2 and remove CO2.
Active pumping movements of abdomen ventilates outer trachea
Describe the circulatory system of insects
Open circulatory system
Hemolymph flows freely within body cavity
Circulates nutrients, hormones, metabolic waste
Has roles in defense: clotting, encapsulation of pathogens
Hydrostatic pressure facilitates hatching, molting, movement in larvae
Heart divided into chambers in the abdomen
Peristaltic contractions drive blood anteriorly into aorta and empties near the brain
Body cavity is divided into 3 compartments (pericardial, perivisceral, perineural sinuses) by the dorsal and ventral diaphragms
Describe the musculature, walking and flight in insects
Muscle attachments to inner surface of exoskeleton
Through tonofibrillae which are discarded with cuticle at each molt.
Inner cuticle strengthened by ridges at attachment site called apodemes
Skeletal muscles are in antagonistic pairs
Flexors bend appendage, extensor starightens appendage
describe the digestive system in insects
Foregut: ingestion, storage, grinding
Midgut: digestive enzymes secreted, digestion, absorption
Hindgut: Absorption of water, salts, amino acids, sugars
The peritrophic membrane compartmentalises phases of digestion
Most insects are oviparous ie lay eggs
Describe the eggs they lay
Eggs can be yolk-poor
Or yolk rich
Yolk is mainly lipid with some protein
What is the ovigeny index?
the proportion of the potential lifetime complement of eggs that is mature upon female emergence
initial egg load/ lifetime potential fecundity
What does an OI value of 1 equal
: linked to high predictability in oviposition site availability
What is Parthenogenesis?
a form of reproduction in which an egg can develop into an embryo without being fertilized by a sperm
Zero time & energy costs of gamete
production, courtship or mate-guarding
Intrinsic rate of (clonal) population
growth doubled.
Describe Haplodiploid sex determination in Hymenoptera
Females develop from fertilised eggs (diploid).
Males develop from of unfertilised eggs (haploid).
Describe the functions of flight?
- Escape from predators
- Foraging for food and oviposition sites
- Mate-finding and other social interactions
- Short-range dispersal (within-habitat)
- Long-range dispersal (migration to new habitat)
Where did the origins of wings in insects come from?
• No fossils of winged insects until late Carboniferous (310 MYBP)
• Developed from gills or
protrusions from notum?
• Did they act as solar panels?
• Did they enable sailing over water or gliding flight?
Describe the wing structure of an insect
• No muscle or ‘tendons’ in the wings themselves • Very thin & flat. • 2 layers of exoskeleton ‘sandwiched’ together. • Girder’ system of tubular ‘veins’ (longitudinal & transverse / cross). • Most of the wing is dead. • But many veins are blood-filled & also contain a trachea + a nerve. • Some wing-hairs are sensory
Describe wing coupling
4 winged- insects
ancestral condition is 2 pairs of wings
Phylogenetically basal groups - insects such as dragonflies – wings
operate independently – hindwings have to operate in the wake of
the forewings (potentially reducing flight efficiency)
• Butterflies, moths, wasps & bees – the 2 pairs beat together –
wings are coupled (i.e. front- and hindwings operate as a single unit)
• Coupling is achieved by lobes (butterflies), bristle(s) (moths), series
of hooks (wasps & bees)
Describe some wing modifications
Beetles have a thickened and hardened forewing: elytra
This is used as passive aerofoils and to protect the hindwings
Hair fringes are found in tiny insects
They increase the surface area
At low reynolds numbers, it acts as a foil
Describe the aerodynamics of insect flight
Gliding flight = no flapping which means no thrust
The insect steadily loses height
eg some dragonflies
Flapping =
A) LEV = leading edge vortex
leads to reduced pressure on top of wings
Vortex is altered during rotation of wing from depression
to elevation
B) Downwash produced as in singleoar sculling
C) Wake capture On upstroke, the insect captures energy lost in the wake of the previous flap cycle
What are the two types of flight muscle?
Direct
Indirect
Describe direct muscles
• Basal groups such as dragonflies.
• Upward/downward movement of each wing produced by contraction of
muscles connecting base of wing to thorax ‘floor’.
• Each wing has its own independent power supply of 2 antagonistically
acting muscles.
• The wings do not have to beat in unison (but can do so).
• Problem with this system: wing beat frequency limited to 25 beats/sec
Describe indirect muscles
• Groups such as flies, butterflies, moths, bees & wasps.
• Advantage of this system: overcomes wing beat frequency constraint.
• 2 sets of muscles (vertical & horizontal) ACT ON THE THORAX, not
the wings per se.
• Thorax ‘roof’ (comprised of nota) is less flexible – means that when
muscles contract, the whole thorax ‘box’ changes shape, it ‘clicks’
between two states.
Some indirect muscles are fibrillar (asynchronous), what does this allow?
allows higher frequency wing beat than direct
muscles
Fibrillar muscles automatically contract rapidly after being extended.
• e.g. Hemiptera, Diptera, Hymenoptera
• Once CNS nerve impulses initiate the process, the wing mechanism can
run by itself.
Why is an insect’s compound eyes important in flight?
Flight speed + height
Avoidance of impending obstacles
Pursuit of moving targets (e.g. prey & mates)
Landing on objects (prey, other food, mates)
What ‘fuel’ is needed for flight?
Hymenoptera & Diptera: carbohydrates
(glycogen, trehalose).
• Locusts, aphids: lipids during sustained flight, carbohydrates during short-duration flight.
• Some Diptera & Coleoptera: amino acids, e.g.
proline (but lipids are their ultimate source)
• Fat is the best store of flight fuel – lipids provide twice as much energy as carbohydrates per unit weight.
• Glycogen, the main carbohydrate reserve, is strongly hydrated in its natural state
Do hovering insects expend less or more energy that insects that alight upon flowers?
Considerably more
Nectar ‘intended’ for continuous hoverers is very sugar-rich
