Insects Flashcards
What defines an insect?
- 6 legs at some point in their life (some exceptions)
- Body divided into 3 tagma (head, thorax & abdomen)
- 1 pair of antennae
- All winged inverts are insects
- not all insects have wings
Why are insect herbivore - plant interactions important
- Nutrient recycling
- Crop yield
- Community structure
- Biodiversity
First insect fossil
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Palaeodictyoptera
Found in the carboniferous - Modern mayflies and dragon and damselflies resemble
Where did insects come from? Arthropod origin theories?
Solution 1: Arthropods have several origins?
Solution 2: Arthropods have a single origin?
Solution 1: Arthropods have several origins?
- Sidnie Manton → similarities in arhtropods were due to constraints imposed by a rigid exoskeleton.
- Differences in the limb morphology
- Uniramous / biramous
- Uniramia hypothesis
- Convergence of several traits associated with the shift to land
Solution 2: Arthropods have a single origin?
- Group called the ‘Cladists’ - believe that similarities in the arthropods are the best traits to use (Monophyly).
- Pan crustacea hypothesis
Which gene gave evidence for how arthropods and insects arose?
- Brain and nervous system of arthropods is closer to crustacea than worms
- Developmental genetics distal-less gene - determines limb branching
- Insects and crustacea have same gene but is regulated differently
- Second hypothesis is now widely accepted
Zero marine insects and very few terrestrial crustacea
So what gave rise to insects ?
Most likely a crustacean
How insects are adapted for terrestrial life: Transitional habitats
bridging habitats
- Estuary
- Marsh
- Intertidal zone
- Mangroves
All slightly saline
The challenges of terrestrial habitats and how insects overcame them.
- Water loss (probably solved by cuticle) - epicuticle
- Integument - living structure with production of wax
- Balance of electrolytes solved with malpighian tubules
- Respiration - not sure how this evolved - trachea (relatively unique). Spiracles
The insect integument
The integument is the outer layer of the insect, comprising the epidermis and the cuticle
- Chitin based
- Extensive sclerotization
- Tough / flexible
Differs from crustacea
- no calcite
- more extensive protein x-links
- waxy epicuticle
What makes the insect integument interesting?
- It is a living structure
- Wax on outer layer is continuously being refreshed
Aquatic insects
- Aquatic insects have had to come up with workarounds for the trachael system.
E.g. Moquito larvae:
- The larva lives in water but breathes air through a siphon that penetrates the water surface, or, in some species pierces the roots of aquatic plants such as cattails.
Synampomorphies
Shared Traits
How are insects adapted to the increased impact of gravity in terrestrial habitats?
- Have a stable gait - move alternative legs, 2 legs on one side to 1 leg on the other (tripod gate) 3 legs always touching ground
- Small body size because of this
Challenges to life on land?
- Respiration
- Water loss
- Support/movement/gravity
- Fertilisation
Synapomorphy
- Character shared by all the descendent species
- Strong evidence for relatedness
Synapomorphies of the Hexapoda (aka what makes an insect)
- Reduction of body segments. Pattern of tagmosiss: 6 segmented head, 3 segmented thorax, 11 segmented abdomen.
- Reduction in leg segments (fusion of the patella and tibia)
- Two primary pigment cells of the ommatidia.
- 9+9+2 pattern of microtubules in sperm flagellum
Apterygota
Wingless insects
Pterygota
Winged insects
How to group basal insect lineages?
Two ways of grouping
1. Arrangements of the mouth parts
2. Or if they have wings or not
Entognatha features
e.g.springtails
Lineages within Apterygota
- Enclosed mouth parts
- Virtually all have eversible vesicles of some kind (organs than can be turned out of the body
- Very small
- Underdeveloped malpighian tubules
- Reduced or absent compound eyes
Entognatha species
Lineages within Apterygota
- Collembola (springtails),
- Diplura (bristletails),
- Protura
Zygentoma
Lineages within Apterygota
Silverfish and Firebrats
Protura order
(within Entognatha)
- Simplest insect
- Antennae lost
- Eyes absent
- Elongated body
Oder Diplura
(within Entognatha)
- Simple oceli (no compound eye)
- Antennae
- Wingless
- Two prominent cerci (long tails)
Order collembola (springtails)
(within Entognatha)
- Fuculum (forked abdominal spring tail folded)
- Compound eye
- Antennae
- Wingless
- Collophore - Electrolyte balance, water uptake, adhering to surfaces etc.
3 innovations that spurred insect diversity
- Evolution of wings
- Evolution of wing folding mechanisms
- Holometabolism(metamorphosis)
How did the variety of wings arise?
Two debated origins
Evolution of wings: Pterygota
Paranotal hypothesis
- Wings arose out of thorax (outgrowth)
Pleural hypothesis
- Gills that gave rise to wings
- Gene responsible for suppressing wing formations found in crustaceans
How did the variety of wings arise?
Two debated origins
Which is correct?
- Still much debate, possibly a mixture of both?
- Duel-origin: Wings are derived from selective regulation of HOX genes in tissue from the thorax and the pleural zones
What was the intermediate function of wings? (how/why did they evolve)
- Courtship
- Thermoregulation - flap to cool
- Aerodynamics
- Respiration
- Possible evolved as a water surface skimming function
what is the indirect form of flight power in insects?
- Most insects dont directly use muscles to power flight
- Insect pterothorax
- Flight is powered by contorting thorax using dorso-longitudinal muscles and dorsoventral muscles.
- This causes the notal hinge to snap open or shut.
Paleoptera:
- Basal lineages,
- Unable to fold wings back over body
- No olfactory bulb in the brain
Mayflies
Paleoptera → Ephemeroptera
- 2500 species
- Aquatic with elaborate gills
- Greatly reduced hindwings
- Important prey item as they emerge on mass
- Emergence attuned to temperature
- Very threatened by climate change
what are Odonata?
Paleoptera → Ephemeroptera
Dragonflies and damselflies
Odonata synapomorphies
- Large compound eyes for predation
- Internal fertilisation
- Modified jaws of larvae
- Rectal gills – dense tracheae system, water drawn in muscularly
- Caudal gills (external)
- jet propulsion
Odonata eyes and brain
- No optical nerve insects
- Ommatidium
- Different sections of the ommatidium have different pigments
Odonata Copulation
- All male winged insects have a aedeagus - derived from a paired appendages on the 9th segment of the abdomen
- Scooping out sperm of other males
- Have secondary genitalia
Neoptera
- Ability to fold wings
- indirect flight muscles
- Monophyletic group
Postembryonic development
- Ametabolous - only relevant in apterygota
- Hemimetabolous
- Holometabolous
The Egg
Life-cycles and Development
- Eggs differ between species
- Some lay live young (aphids)
Postembryonic development: Ametabalous
Life-cycles and Development
- Only relevent in apterygota (wingless insects)
- Series of moults from egg to adult which allow growth
- Gradual change in body size but body form stays the same
Postembryonic development: Hemimetabolous development
Life-cycles and Development
- Adult form has fully formed wings
- Distinction between adult and nymph
E.g. crickets / nymphs
Postembryonic development: Holometabolous development
Life-cycles and Development
- Ecology of adults differs largely from larvae
E.g. Butterflies & Moths - Non-feeding stage called a pupa between immature larva and adult
- Adult structures develop as imaginal discs inside larva
Nomenclature
Life-cycles and Development
- Sets of stages (moults ect) are called instars
- Different insects have different numbers of instars
- Penultimate instar subimago
- Final instar - imago
Instar variation
Life-cycles and Development
- Instar variation - some have 30+ some 5, some 4 etc
- Some species have fixed number of instar
- Some species can add an extra instar if they haven’t got enough nutrients
Groups within Hemimetabola
Hemimetabola. Basal neoptera (basal winged insects)
- Stoneflys (Plecoptera)
- Stick insects (Phasmatodea)
- Grasshoppers & Crickets (Orthoptera)
- Mantises (Mantodea)
- Cockroaches (Blattodea)
- Termites (Isoptera)???
- Thrips (Thysanoptera)
- True bugs (Hemiptera)
- Aphids, white flys.. (Sternorrhyncha)
- Cicadas.. (Auchenorrhyncha)
Stoneflys (Plecoptera)
Hemimetabola. Basal neoptera (basal winged insects)
- Reduced ovipositor
- Accessory heart (pulsatile organ) associated with cerci
- 3-segmented tarsi
- High O2 requirement
- Adapted for aquatic life
Stick insects (Phasmatodea)
Hemimetabola. Basal neoptera (basal winged insects)
- All herbivores
- Example of crypsis (mimic sticks - appearance and behaviour)
- Claspers present in males
Grasshoppers and crickets (Orthoptera)
Hemimetabola. Basal neoptera (basal winged insects)
- Cryptopleuron (lateral extension of the pronotum)
- Saltorial hindlegs (jumping)
- Wings inclined over abdomen at rest (folding wing mechanism)
Mantises (Mantodea)
Hemimetabola. Basal neoptera (basal winged insects)
- Enlarges raptorial forelegs
- Femoral brush on front leg
- Extraordinary head mobility
- Ootheca (egg mass) embedded in protective froth
Common features
- Camouflage and mimicry
- Cyclopean metasternal ear
Cockroaches (blattodea)
Hemimetabola. Basal neoptera (basal winged insects)
- Wrap around eyes
- Dorsoventral flattened
- Slightly hardened, leathery (coreacious) front wings
Maternal and biparental care
- Adults protect nymphs
- Extended maternal care
- Retention of the ootheca (egg sac) (may be first step towards parental care)
Termites (Isoptera) < no longer an order - Evolved from cockroaches.
Hemimetabola. Basal neoptera (basal winged insects)
- Evolved eusociality (different roles in colonies)
- No specific synapomorphies for termites
Termite mounds - thermoregulation
- Chimneys and tubes which drag air up from the colony - improves air flow
- Evenly distributed as as they compete for resources (evenly distributed colonies)
- Increase nitrogen levels around mounds- linked with even distribution of plant growth
Thrips (Thysanoptera)
Hemimetabola. Basal neoptera (basal winged insects)
- Frilled wings (setae)
- Right mandible reduced - left mandible inflexible
- Pre-adult instar -
- Haplodiploid (males from unfertilised eggs)
Hemiptera (True bugs): Synapomorphies
Hemimetabola. Basal neoptera (basal winged insects)
- Mouth parts fused to form piercing, sucking beak or rostrum
- Herbivorous
- Major plant pests
- Disease vectors
- Viviparity and parthenogenesis in some groups
Hemiptera - Plant juice issues
Hemimetabola. Basal neoptera (basal winged insects)
- Phloem sap - contains very little nitrogen - positive pressure
- Xylem fluid - negative pressure - leaf transpiration - low nutrient
- Negative pressure - difficult to get out - insects have to actively work against pressure
- Formation of beak - large muscles in head
Sternorrhyncha: psyllids, aphids, whiteflies, scale insects
Hemimetabola. Basal neoptera (basal winged insects). HEMIPTERA
- Fine, hairlike stylets
- Parthenogenetic viviparity
- Reduced or lost ovipositor (birth live young)
- Phloem feeding + honey dew secretion
Auchenorrhyncha: Cicadas, cercopids, membracids, fulgoroids
Hemimetabola. Basal neoptera (basal winged insects). HEMIPTERA
- Elaborate acoustic organs on legs
- Enlarged clypeus (forehead)
- Cibarial pump
- Xylem feeding
Eusociality
Depends on high levels of altruism within groups as individuals increase the fitness of others at a cost to themselves (e.g., by helping care for young).
Heteroptera: Shield bugs
Hemimetabola. Basal neoptera (basal winged insects). HEMIPTERA
- Beak attached to front of head
- Hemelytrous forewings
- Leathery wings
- Flat folded wings, overlap abdomen
- Scent glands on nymphs (anti-predator)
- Some are predators
The 4 big insect orders
Holometabola
- Coleoptera
- Lepidoptera
- Hymenoptera
- Diptera
Coleoptera (Beetles)
Holometabola
- Very diverse
- 40% of all insects
- Broken up into 4 suborders
- 166 families
- 400-420,000 species
- Diversity in morphology, ecology and behaviour
Coleoptera: Synapomorphies
- Hardened front wings - elytra
- Large hind wings with specialised venation for tucking and for power flight (allows them to have very large hind wings)
- Reduced thorax
- Retracted genitalia
Beetles are all very similar in overall appearance - few deviations
Coleoptera: Elytra
- Access to hard habitats and spaces - burrow into wood, leaf etc
- Wing protection
- Infection and predation protection
- Homeostasis (desiccation, cold)
Key morphological adaptation that allowed massive radiation
Coleoptera: Beetle Ecology Variety
- Most are herbivorous (roots, stems, leaves)
- Fungivorous
- Predaceous
- Peculiar diets (e.g. pure cellulose/lignin; dried grain)
- Parasitic – very uncommon
- Repeated evolution of aquatic adaptations (plastrom - air bubble, used as gill)
Coleoptera sub-orders
- Adephaga
- Polyphaga
- Archostemata
- Myxophaga
Adephaga
Coleoptera sub-order
- Mostly predacious
- Diving beetles are mostly predatory
- Dominated by carabidae (ground beetles) and aquatic (diving beetles)
E.g. Bombardier beetles → spray out anti-predator chemical weapon
Polyphaga
Coleoptera sub-order
- Herbivorous
- Form bulk of the coleoptera
- E.g. dung beetles, stag beetles
Insect sensory perception (4 types)
- Chemoreception
- Mechanoreception (tactile)
- Thermal and hygroreception (heat)
- Visual reception
Chemoreceptoin (2 kinds)
- Olfactory - gas phase
- Contact - liquid phase (contact based)
Sensillae - detect the signals (found on antennae, mouthparts, legs
Sensillae
Insect sensory perception
- Punctured with pores that allow gas to flow in.
- In most insects the part of the brain associated with chemical signals is the largest part of the brain
- Variable sensitivity
Chemoreception olfaction
Insect sensory perception
Important for long distance communication & detection of mates, resources, predator warning
Semiochemicals (information chemicals)
- Pheromones (within-species communication)
- Allelochemical (between species communication)
Pheromones
Within-species communication
Allelochemical
Between species communication
Striped ambrosia beetle and other beetle that inhabit the same tree
Chemoreception
Detects other beetles pheromones that colonises the same tree to find a tree for themselves.
Mechanoreception (tactile)
- Perception of any mechanical distortion of the body
- Allows insect to orientate themself
- Touch, vibration, strain, stress
- Huge range of sensitivity trichoid sensillum
Trichoid Sensillum
Mechanoreception
- Hairs on insect are attatched to peg below surface.
- When hairs touch something the peg is stimulated and caused the scolopale to activate attached nerve cells
- Nerve then sends signal
Visual systems
Insect sensory systems
- Ocelli - simplified eyes - generally one lens - multiple rhabdomes - allows response to changes in day length
- Stemmata - found in larval insects - provide basic orientation - very simple eye
- Compound eye
Thermo and hydro-reception
- Heat and water detection
- Water balance and temperature
- Very little know about these receptors
Lepidoptera synapomorphies
- Glossa - long mouth part
- Wing setae modified to form scales (modified hairs)
- Median ocellus lost
- Vom Rath’s organ - sensory organ
- Fore tibial brush
Lepidoptera: Glossa / Proboscis
- Proboscis uncoiling is operated by a pump system
- Actively pumps hemolymph into the proboscis to extend it.
- Powerful cibarial head pump (can suck up half it’s body weight in a single feeding even)
Lepidoptera: Variation in the proboscis
- Some variation in the proboscis
- Some used for other things - some use hook tip to suck out juices of cells
Caterpillar legs
- Six true legs
- Prolegs at the back used to hold onto plants (not true legs)
Silk moth domestication
- First domesticated insect
- Can’t survive in the wild anymore
- Destructive practice → larvae killed
- First sex pheromone synthesis
Largest suborder of lepidoptera ?
Glossata (125 families)
Glossata synapomorphies
- Double layer of wing scales
- Frenate wing coupling (frenulum)
- Frenulum - spur more secure than other types of wing couplings
Moth and butterflies in conservation
- Highly reliant on nectar because of glossop
- Highly threatened by climate change
- Declines in moth species richness with increased greyspace (urbanisation)
- Declines in bees and hoverflies too - moths showed largest decline
Hymenoptera
Bees, wasps & ants
Wasps are most prolific
Evolution within the Hymenoptera
Repeated evolution of:
- Parasitism
- Nectar feeding
- Eusociality
Hymenoptera Synapomorphies
- Unique labio-maxillary complex (sucking tongue/glossa)
- Apical, tibial spur (antennal cleaning). Wasps.
- Hamuli (wing coupling mechanism) locking system allows them to be good flyers
- Haplodiploid (haploid males from unfertilised eggs, diploid females (fertilised)
Hymenoptera feeding habits
- Can feed on a variety of things
- Chewing mandibles are common
- Also sucking tongue
Symphyta
Major Hymenoptera groups
- Basal group
- Herbivorous caterpillar like larvae
- Sawfly and Woodwasps
Apocrita
Major Hymenoptera groups
- Evolution of the wasp waist
- Apodous larvae - legless larvae
Chalcidoidea - tiny group within Apocrita
Major hymenoptera groups
- Small to minute size (~1-2mm)
- Parasitoids and hyperparasitoids of other insects
- Phytophagous in galls
- Fig wasps (Agaoninae) are herbivores
- Hairs on wings no veins
Ichneumonoidea: group within Apocrita
Major hymenoptera groups
- Parasitoids of other insects
- Notable, often extreme ovipositors
- Important natural enemies of herbivorous insects (biocontrol)
Ectoparasitoid
Feeds externally on host, host is paralyzed.
Endoparasitoid
Feeds internally on host, via oviposition
Primary parasitoid
Parasitizes the primary host
Hyperparasitoid
Parasitizes a primary parasitoid
Vespoidea
Major groups in the Hymenoptera
Wasps and ants
Formicidae (ants)
within Vespoidea
- Numerous independent origins of eusociality
- Predacious and herbivorous
- Large colonies
- Farm fungus - Parallels between human agriculture
Apoidea (bees and apoid wasps)
- Veggie wasps
- Evolved to use pollen and nectar as food
- Scopa - for pollen carrying (hairs that allow sticky adhesion)
Corbiculates
- Have a pollen basket (corbicula)
- All bees that store honey (edible to humans)
The significance of honey bees
- Livestock - highly domesticated
- Perception of honeybees as ‘wild’
- Outcompete wild species of bees
- Disease spreaders
Largest family of bees
Apidae (e.g. bumble bees)
- Most bee species are solitary
- Few parasitic
- Few eusocial
Bee lifecycle (solo)
- Excavates a chamber
- Collects pollen (pollen ball)
- Lays egg on pollen ball
- Larva hatch and feed on pollen ball
- Turns into pupa
- Emerges when an adult
Cuckoo bees lifecycle
- Finds an already dug and prepared nest (of another bee)
- Lays egg on the pollen ball
- First instar larval stage can have hook-like mouthparts to kill other larva
Primitive eusocial
- Not as much dimorphism
- Only size differs between queen and workers
- Decisions made by one individual
Advanced eusociality
- Morphologically distinct worker and queen
- Swarming: group decisions
Evolution of Eusociality
- Termites have very ancient eusociality (triassic)
- Ants then wasps evolved it after
- Bees are the most recent to evolve eusociality
Diptera
The flies
Diptera Synapomorphies
- Loss of hind wings
- hind wings formed into Halteres
- Extreme reduction of the prothorax
Diptera minor synapomorphies
- Apical segment of labial palpus modified to labellum - specialised mouthparts
- Kinked wings
- Apodous larvae - legless larvae
- Reduced abdominal spiracle in adult males
Diptera: Major groups
- Nematocera: Basal long-horned flies. (e.g. crane flies)
- Brachycera: Short-horned flies (e.g. houseflies)
- Clyclorapha: Hoverflies
Origins and evolution within Diptera
Many different origins of feeding habits
- 12 blood feeding origins
- 17 endoparasitism
- 10 ectoparasitism
- 18 flightlessness
- 26 plant feeding
Very diverse in both basal and derived lineages
FLIES ARE VERY DIVERSE
