VL 5 Flashcards
Insect mouthpieces
Mandibles - chewing
Proboscis - piercing-sucking or siphoning Labelllum - sponging
Feeding strategies - how are herbivores categorized
Feeding guild - how and where do they eat
Diet breadt - what do they eat
Feeding guilds
Where on the plant dies the insect feed?
- roots, stem, seeds, fruits, leaves
- exophage vs endophage
How does the insect feed?
- Mouthpart type? Chewing or sap feeding
- Gall inducing? Leaf rolling?
Endophage
Feeds inside the plant, such as stem boreres, leaf miners or gall forming insects
Exophage
Feed on exposed locations such as leaves, flowers, pollen, seed heads
e.g. caterpillars, beetles and grasshoppers
Sap feeding
Needle-like mouthparts puncture plant tissue
Manly hemiptera (e.g. aphids)
Can transmit viruses
Diet breath categories
Monophagous: single plant species
Oliphagous: several species in the same family
Polyphagous: species in different families
Coevolution
Two (or more) species which have reciprocally affected each other’s evolution
Speciation due to specialization on a specific host plant can be caused by:
Interspecific competition - niche food resource
Abundance of plant species
High offspring performance
defence against natural enemies
- toxins
- mimicry
Optimal defence hypothesis
Plant defences are costly, taking resources from growth and reproduction. Allocation of resources is therefore in relation to risk of attack, value of the plant tissue and the cost of the defence
Long lived and short lived plants, or plants of the same species in different environments, may invest differently
Types of plant defences against herbivore attack
Nutritional constraints
Mechanical
Chemical
Indirect defences
Nutritional constraints
Maintaining balance of C:N:P is essential for metabolism and cell function
Slow growth, high mortality hypothesis
Counter adaptations for nutritional constraints
Manipulate nitrogen content
- N-rich sites
- Symbionts
- Life cycle sync
- Storage + excretion
- Nutrient sinks
Mechanical and structural defence
Toughness / hardness (dense cell wall or high silica content)
Waxy surface
Crypsis (camouflage) and Refuges
Spines and Trichomes
Trichomes
Mechanical barriers to feeding or oviposition (non-glandular trichomes)
Produce silky substances or toxins that trap or harm herbivores (glandular trichomes)
Counter defence - mechanical and structural
Hardness:
- morphology - larger/specialised mandibles. Extra molts to replace worn mandibles
Trichomes:
- Modified tarsal claws to grasp non-glandular trichomes
- No tarsi to avoid triggering glandular trichomes
- Long proboscis or chewing mouthparts
Waxy:
- Tarsal adaptations like clasping feet, hook structures, suction cups
- Behavioural strategies
Chemical defence
Directly affect insect growth and development
May interfere with insect metabolsim - toxins such as pyrethroids or nicotine. These are cheaper for the plant to produce but lower effectiveness against co-evolved insects
Or can be indigestible or sticky, e.g. tannins, resins and latex. These larger compounds are more costly to produce, but offer better protection as they are difficulta to evolve tolerance for
Chemical - constitutive and iduced
Plants may have constitutive (always present) and induced (produced when attacked by herbivores) defences
Constitutive = baseline protection before herbivores detected
Induced = high levels produced in affected tissues - targeted
Regulated by phytohormones jasmonic and salicylic acid
Constitutive defence
Always present
Provide protection before attack detected
resource costly to grow / continuously maintain
Godd against generalists
E.g. spines, cellulose, alkaloids, trichomes, resins, tannins
Induced defense
Activated by herbivore feeding
Temporarily costly, but only activated when needed
Plant takes damage before defence response
Targeted: Localised to affected tissue and may be specific to insect species
Regulated by phytohormones jasmonic and salicylic acid
E.g. Trichomes, Phenolics, Alkaloids, Natural enemies, Terpenoids, Digestive inhibitors
Jasmonic acid
p. 27
Chewing herbivore damages plant
-> Local production of jasmonic acid
-> Plant produces volatiles to repel herbivores or attract natural enemies
or
Local production of toxins and digestive inhibitors
-> Generalists move to new part of plant / new plant
or
Specialsits counter
Alternate pathway: salicylic acid mainly involved in pathogen defence, but can also produce defences against sap feeding insects. Reduces defence against chewing herbivores
Mutually antagonistic: some insect (including generalist) can induce one pathway to shut down the other
Chemical - priming
Plants receive volatile signals from neighboruing plants under herbivore attack
Priming effect allows activation of induced defence signaling pathways to ready them before herbivores arrive, giving fitness benefit. Priming acts like a vaccination, so that defence will trigger more quickly and strongly on herbivore attack
This can be used in pest management to increase defences against herbivores
Chemical - counter defence
Detoxification enzymes
These can be included in the insect after consuming alkaloid rich food
Filtering and excretion - e.g. Manduca sexta moths eliminate nicotine with a specialized alkaloid transport system in Mlpighian tubules
Sequestration - specific and selective uptake and accumulation of plant toxins. The insect is then toxic to predators. Costly mechanism
Behavioursal deactivation ot avoidance - can deactivate latex / resin channels by clipping veins (common in milkweed plants), trenching or mass attack
Indirect defences - natural enemies
Induced defence - volatile emissions triggered by feeding or oviposition will attract natural predators / parasitoids which will attack the herbivores - mutualism
Indirect defences - natural enemies - counter defence
Some herbivores can suppress volatile emission to prevent natural enemies being recruited
Indirect defences - predator rewards
Plants produce energy rich foods to attract predators of herbivores - extrafloral nectaries and protein bodies
May also have structures that act as domiciles for predators insects - do not attract predators but make it more likely visiting predators may remain
Enemy free space
Insects under high predation / parasitoid pressure -> shift to new local plant -> lower enemy pressure
Host-shifting theory
Herbivore fitness isadversely affected in the presence of enemies
Fitness is greater on a novel host in the presence of enemies
In the absence of predators, insects may still have greater fitness on the ancestral host
Enemy free space
see slides 39 - 44
