Insects Flashcards
Are insects arthropods?
yes
What features do insects have in common with other arthropods?
- segmented body plans
- exoskeleton
- moulting
- jointed legs
Trends in Arthropod Evolution
- loss of segments
- specialisation of segments
- tagmatisation (grouping of segments with related functions
Origin of Insects
- insects are 6 legged crustaceans
- became specialised for freshwater
- became specialised for land
Remipedia
Charactaristics
- 30 known extant species
- live in salt water caves
- primitive
- more closely related to insects than other crustaceans
What is the difference between crustaceans and insects?
Crustaceans have biramous (branched) limbs and insects have uniamous limbs. The inner branch may have become gills and then wings
Apterygota
- Archaeognatha and Thysanura
- no wings
- no metamorphosis
- remnant abdominal appendages
- 3 ‘tails’
- spermatophores
Archaeognatha
- Bristletails
- single condyle mandibles (unlike all other)
- often jump
- members of Apterygota
Thysanura
- Silverfish
- two condyle mandibles (like all other insects)
- flattened runners
- members of Apterygota
Winged Insects
Paleoptera and Neoptera
Paleoptera
- Mayflies and Dragonflies
- cannot fold wings back over abdomen
- wings have many vains
- beat independently which is inefficient
Neoptera
-Exopterygotes and Endopterygotes
-all other winged insects
-can fold wings back
-
Exopterygotes
Blattodea - cockroaches and termites
Orthoptera - grasshoppers
Hemiptera - true bugs
Endoptergotes
Coleoptera - beetles
Hymenoplera - wasps, bees, ants
Lepidoptera - butterflies, moths
Diptera - true flies
What are the 3 types of insect life cycles?
Ametabolous (Apterygota)
Hemimetabolous (Exopterygotes)
Holometabolous (Endopteryrgotes)
Ametabolous Life Cycle
- larva hatches from egg
- larva moults going through a series of nymph stages
- head shrinks proportionally as larva grows
- adult looks like larva but bigger
- no metamorphosis
- keeps moulting in adulthood
Hemimetabolous Life Cycle
- larva hatches form egg
- larva goes through 5-8 moults
- wing buds develop on the outside
- adult has wings and does not moult again
- partial metamorphosis
Holometabolous Life Cycle
- maggot hatches from egg
- goes through several moults
- wing buds develop inside the body
- pupates
- adult has wings and does not moult again
- complete / dramatic metamorphosis
What happens when a maggot pupates?
- no eating or movement
- -highly metabolically active
- insides broken down
- previously dormant cells multiply
Insects Through Time
Devonian
- 400-350 mya
- early land plants
- bristletails
- pre spiders
- possible first winged insects
Insects Through Time
Carboniferous
- 300-350 mya
- high oxygen concentrations
- giant horsetails and tree ferns
- giant pre dragonflies
- paleoptera with third sets of wings
- pre cockroaches
Insects Through Time
Permian
- 250-300mya
- extinct winged orders still present
- primitive reptiles
- horsetails
Insects Through Time
The Great Extinction
- greatest mass extinction event ever
- ecological space for rise of the dinosaurs
- many insect orders end
- holometabolons survive and diversify
Insects Through Time
Triassic
- 200-250mya
- early examples of modern orders
Insects Through Time
Jurassic
- 150–200mya
- modern orders but now extinct families
Insects Through Time
Cretaceous
- 150-64mya
- feathered dinosaurs
- Neuroptera and Hymenoptera
- insects act as pollinators
- coevolution of insects with flowering plants
Insects Through Time
Eocene
- 55-35mya
- Baltic amber forest
- mammals
- diatryma (birds)
- hemipteran
- butterflies
Which organisms are insects derived from?
crustaceans
Amber
- fossilised plant resin
- best known from Baltic area
- preserves small animals
- can infer ecological interaction
- -parasite on organisms
- -organisms trapped in close proximity to each other
- Why are insects important?
- dominate terrestrial and freshwater biodiversity
- can transmit diseases
- some feed on animals
- pollination
- Drosophilia (fruit fly) is THE model animal organism
- There are lots of them but they are small
- more than 50% of all described species are insects
- it is estimated that only 1/5 of insects have been describes
- most are 2-3mm in length
- Insects are Octhropods
- jointed limbs
- exoskeleton made up of plates
- intersegmental membrane that attaches plates together is what allows joints to bend
- Adult Insects Usually Have Wings
- two pairs of wings on second and third thorax segments
- wings are probably modified gills, which were modified second leg branches
- some of the same genes are involved in both larval wing and larval gill development
- Arthropods Moult
- have to moult or exoskeleton puts a limit on how big they can grow
- immediately after moulting, lose water more rapidly, unable to fly, find it difficult to walk
- a less rigid exoskeleton allows insects e.g. maggots to grow in between moults
- in primitive insects, moults only produce larger almost identical copies
- Insects Are Segmented
- body plans based on repeating units
- basic body plan:
- -head
- -3 segment thorax
- -abdominal segments
Insect Head
- originally 6 segments, now fused together
- specialised for feeding and sensory detection
- antenna
- eyes
- ‘teeth’ outside bdy
Insect Mouth Parts
- Mandibles - jaws
- Maxilla - inner branch, small set of jaws and sensory palps
- Labium - lower lip, like two maxilla fused together, used as a spoon to push food into the mouth, palps
- Labrum - upper lip, like labium but without palps
Nervous System
- ‘Brain’ - collection of ganglia fused from original brain segments
- ventral nerve cord
- ganglion (concentration of nerve cells) in each segment
Thorax
- specialised for locomotion
- lots of muscle
- 3 pairs of legs
- wings
Abdomen
- specialised for metabolism and reproduction
- appendages mostly lost
- at the tail end, several segments are fused together and specialised for reproduction
- Most Insects Display Metamorphosis
- extreme metamorphosis is seen in advanced insects
- maggot -> larger larva -> pupa -> fly
- Insects Reproduce Sexually
- separate males ad females
- males and females can look the same or different
- not all insects are sexually dimorphic
9.. Respiration
- more O2 in the atmosphere allow insects to grow bigger due to limitations in their respiratory systems
- spiracle - external opening to the respiratory system
- pump bodies to squeeze air sacs approximating breathing
- air travels down main trachea and then along tracheal branches to tracheoles which get narrower and narrower until they can enter cells
- very efficient over distances less than 1mm but gets less efficient the bigger the insect is
- Circulatory System
- open blood stream
- ‘heart’ - tube lined with muscles that can contract
- has valves to direct blood flow towards the brain
- aorta carries blood from heart to brain
- haemocoel - body cavity, organs hang in the haemocoel which fills with blood
- oxygen etc. moves by diffusion through haemocoel back to heart
- almost no veins or arteries
Insect Feeding Through Time
- scavengers feeding on decayed plants and animals or detritus
- chewing evolved before sucking
- dead plants eaten before live plants as living plants are often well defended but nutrient poor
Larval Feeding
-stage where most growth happens so where most biomass is removed from environment (most damage done)
Exopterygote
Definition
larvae and adults eat similar food
Endopterygote
Definition
larae and adults eat different food
Biting and Chewing
Basal Mouthparts
Labrum - upper lip
Labium - lower lip (palps)
Maxilla - palps
Mandible - jaw
Mouthparts in Predators
- usually have large mandibles
- legs can be used instead of jaw so insects don’t have to have large mandibles to be predators
Weevil
- mouthparts at the end of a long proboscis
- chew deeply into plants
- lay eggs inside hole in plant
Liquid Diets
- phloem and xylem
- individual cell contents
- insides of prey
- blood
Modification of Mouthparts for a Liquid Diet
- mandibles and part of maxillae modified to form stylets
- stylets are cartlidge rods that can be stabbed into prey
- rest of maxillae form inner/maxillary stylets
- there is a salivary canal between the inner stylets
- saliva is pumped down a ventral channel and digested food is sucked up the dorsal channel
- sensory palps lost
- labium and labrum enlarged to protect stylets
- Cibarial pump - vaccum pump, muscles contract creating a partial vaccum inside the mouth drawing liquid up
Filter Chamber
-loop in gut
-food passes around the loop
-but water is able to skip the loop by crossing the small gap between the beginning and end of the gut
-
Why do liquid feeding insects need a filter chamber?
- liquid food is very high in water content
- in order to ingest enough nutrients, insects end up taking in way to much water
- this is bad for many reasons e.g. enzymes don’t work as well at low substrate concentration
- filter chamber allows excess water to be quickly passed out of the body
Uses of Excess Liquid in Insects
- sweat
- cuckoo spit - soap added to water as it leaves the body causing it to froth and insect can hide in it
- honeydew - phloem feeding insects also ingest excess sugar so release water and sugar, ants eat honeydew, and ants distract parasitic wasps from insects
Lepidoptera Mouthparts
Caterpillars -primitive chewing type with mandibles and maxillae Butterflies -mandibles lost -maxillae form short proboscis
Why feed on nectar?
-easier to reach than phloem, xylem or blood as the skin doesn’t have to be pierced
Hawk Moths Mouthparts
- proboscis elongated
- evolution of plants to have longer flower led to coevolution of the hawk moth
- proboscis curls up when not being used to protect it
- this happens when there is no pressure inside the tube, it automatically curls
Diptera (Robber Fly) - Feeding
- spiky legs to catch and kill prey
- sucks liquid contents of prey
Mosquitoes
- feed on blood
- relatively specialist, feed on specific species
- abdomen fills with blood
- presence of blood in abdomen required for egg development
- lays eggs in/on water
- transmit many diseases
- females only feed on blood
Mosquito Larvae Feeding
- feed in liquid
- filter feeders
- complex set if spines/hairs on mouthparts
- mouthparts move and hairs draw water across the head
- other mouthparts act as sieves and others scrape the collected food into the mouth
Mosquito Pupa
- doesn’t feed
- is alive
- can swim
- has eyes and respiratory tube
Male Mosquito Adaptations
- many branches on antenna
- increase in surface area to detect female ferimones
Female Mosquito Mouthparts
- maxillary and mandibulary mouthparts both for cutting
- stylets stick into prey
- labium protects stylets when not feeding
- hypopharynx = straw
