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Entomology > Insect Interactions (herbivory) + Ecosystem services > Flashcards

Insect Interactions (herbivory) + Ecosystem services Flashcards

1
Q

What are ecosystem services?

A
  • benefits from resources + processes supplied by ecosystems
  • UN 2005 Millennium Ecosystem Assessment (MA)
  • analysed state of Earth’s ecosystems
  • provided summaries + guidelines for decision-makers
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2
Q

Ecosystem functions maintain ecosystem services

A

incl physiochemical + biological processes occur within the ecosystem to maintain ecosystem services

higher biodiversity stabilises + diversifies ecosystem functioning

composition + diversity of functional traits that appears to be the best predictor of ecological processes

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3
Q

what are functional traits?

A

morphological, physiological, phenological or behavioural characteristics of organisms

influence performance or fitness through effects on growth, reproduction + survival

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4
Q

Insects as ecosystem service providers

A
  • insects affect nutrient cycling directly and indirectly
  • reduce net primary production through herbivory + breakdown of litter via detritivores
  • important roles as ecosystem engineers
  • indirectly, they may affect species composition
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5
Q

Ecosystem functions via insect interactions w/ plants

A
  • insects have most interactions w/ plants
  • these interactions will have significant effect on ecosystem functioning
  • consider herbivory + mutualisms (pollination)
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6
Q
  1. herbivory - phytophagous orders
A

1/2 all insects species = phtophagous

most herbivores from 9 orders:
1. Orthoptera
2. Phasmatodea
3. Lepidoptera
4. Coleoptera
5. Thysanoptera
6. Hemiptera
7. Pscocoptera
8. Hymenoptera
9. Diptera

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7
Q
  1. Herbivory - categorising herbivores
A
  • plants support complex assemblage which exploit every part of plant
  • insect categorised by:
    • diet breadth - host plant range - mono/oligo/polyphagous
    • feeding guild - chewers/sap feeders, free-living/concealed
  • respond differently to plant nutrition, allelochemical + natural enemy attack
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8
Q
  1. herbivory - free-living chewers
A
  • free-living chewers eat exposed plant parts, e.g. leaves, flowers, seeds
  • most numerous mandibulate insects are Coleoptera + Lepidoptera (Larvae)
  • Orthoptera, Hymenoptera + Phasmatodea are next numerous
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9
Q
  1. Herbivory - concealed chewers
A
  • concealed chewers incl Lepidoptera, Coleoptera, Diptera, Hymenoptera
  • Leaf tiers, rollers + miners feed internally between upper and lower leaf epidermis
  • wood and stem borers feed on bark, cambium, sapwood or heartwood of branches + trunks
  • fruit + seed/pod borers
  • mandibulate herbivores also cause gall formation by oviposition and feeding
  • root feeders may be borers or external feeders
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10
Q
  1. Herbivory - free-living sap-feeders
A
  • insert stylets into various plant tissues
  • phloem feeders - aphids, plant-, tree- leafhoppers, scale insects
  • Xylem feeders - cicadas, froghoppers
  • epidermis/mesophyll/parenchyma feeders - thrips, Heteroptera
  • gall-inducers
  • some sap-feeders also feed on roots
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11
Q
  1. herbivory - aquatic system
A
  • aquatic systems use functional groups
  • mandibulate herbivores
  • sap feeders, e.g. lesser water boatman (Corixidae)
  • Shredders feed on living or decomposing plant tissues - some stoneflies
  • collectors feed on plant fragments + small bits of organic matter
  • divided into gatherers (mayfly larvae) + filter feeders (Blackfly larvae - Simuliidae)
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12
Q

Additional indirect injury

A
  • salivary or other toxins may be injected that may cause infection
  • e.g. European wood wasp, Sirex noctilio, injects venom into conifer hosts causing lethal fungal infection
  • sap-sucking and root- and shoot-feeders may increase transmission of viruses, bacteria, fungi + nematodes
  • economic significance
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13
Q

Plant defences from herbivory

A

a) plant nutrition
- N and P limited

b) Mechanical and structural barriers
- toughness + hardness
- Trichomes
- Surface waxes

c) Allelochemical barriers
- secondary metabolites

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14
Q

a) plant nutrition

A
  • ecological stoichiometry = study of relative balance of elements in organisms at different trophic levels - C, N, P
  • plants = nutritionally inadequate, limited in N and P
  • Deadwood has lowest concentrations, seeds the highest
  • creates nutrient imbalances and affects growth
  • herbivores have higher N + P levels than plants
  • homeostatic mechanisms eliminate excess C and allow selective uptake
  • Honeydew allows excess sugars to be removed while selective uptake of amino nitrogen using filter chamber
  • consistent population increase on N- enriched plants by sap-feeders
  • response by chewers less obvious
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15
Q

The counter evolution

A
  • feeding compensation by increasing feeding rate
  • selection of N-rich feeding sites - young, growing leaves, flowers, seeds
  • life-cycle synchronisation of reproduction + development w/ optimal plant nutrition (time and space)
  • manipulation of plant physiology forming nutrient sinks, e.g. gall development
  • nutrients from non-plant sources
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16
Q

b) mechanical and structural defences

A
  • toughness + hardness
    • hardness = initial cracking/splitting of tissue
    • toughness = resistance to crack growth
  • cellulose microfibrils in hemicellulose / lignin matrix
  • Amorphous silica in leaves, spines or trichomes
  • deter from feeding but also cause abrasion and mandibular wear
  • sap feeders likely less affected by tissue toughness
  • Trichomes have a diversity of forms, sizes and densities - non-glandular and glandular
  • also insulate leaves, reduce evaporation + aid water + nutrient absorption
  • reduce oviposition, alter movement -> reduce growth + fecundity
  • hooked trichomes cause injury to Lepidoptera larvae leading to loss of haemolymph, desiccation and death
  • surface waxes protect against desiccation and pathogen invasion
  • slippery surface prevents attachment in some Lepidoptera larvae + aphids
  • some herbivores can maintain attachment, e.g. Phyllotreta cruciferae
  • interactions between surface wax structure + tarsal morphology prevents certain species attaching
17
Q

The counter evolution

A
  • relative head size of chewers of grasses (silica) e.g. grasshoppers, caterpillars
  • extra moults to replace worn mandibles and chisel-edged incisors
  • specialised tarsal claws or long proboscis for trichome-bearing leaves
  • tarsal modification for waxy leaf surface e.g. chrysomelid beetles
  • Empoasca leafhoppers produce suction cup w/ tarsal pads
18
Q

c) Allelochemical barriers

A
  • Insecticidal properties of plants long known, e.g. rotonene (Fabaceae) - 1848, tobacco - 1690, pyrethrum (Asteraceae) - 1880
  • action of secondary metabolites more recently discovered (1940s - 1970) - play little/no role in plant growth and reproduction
  • thousands isolated from plants - clear defensive role, but also other functions e.g. protection from UV, storage + signalling compounds
  • allelochemical diversity -> different to categorise
  • Qualitative / quantitative or toxins / digestibility reducers
  • qualitative / toxins interfere w/ metabolism, e.g:
  • Alkaloids - Deadly nightshade (atropine), tobacco (nicotine)
  • Pyrethrins - chrysanthemum
  • Cyanogenic compounds - Prunus sp.
  • Quantitative defensive compounds reduce digestibility
  • e.g. tannins, resins, latexes, cellulose + silica
  • most herbivores unable to digest cellulose and lignin
  • larger molecules - more costly to produce, but provide better protection as are dosage dependent
  • tannins occur mostly in woody plants but also some grasses
  • when insects bite leaves cause chemical reaction to prevent availability of protein
  • resins secreted from glands or trichomes or may be held in ducts or canals
  • latexes contained in specialised cells
  • gum-up mandibles but also contain toxins
  • constituent defences may always be present in the plant
  • but many secondary metabolites and trichomes may be induced by feeding
  • e.g. defensive proteins, phenolics, terpenoids, alkaloids + indole glucosinolates
  • preformed chemicals or activated synthesis
  • direct signalling or ‘eavesdropping’ neighbouring plants
19
Q

Volatile Organic Compounds (VOCs)

A
  • secondary metabolites
  • emitted by plants as a consequence of interaction with biotic and abiotic factors
  • very important role in plant evolution
  • floral VOCs often involved in defence and pollinator attraction
  • act as repellents or for indirect defences (attracting parasitoids and predators)
20
Q

The counter evolution

A
  • Detoxification - most frequent mechanism uses enzymes to degrade allelochemicals
  • high pH, surfactants or redox potential can reduce effect of tannins
  • development of alternate proteinases not affected by inhibitors
  • Excretion - Malpighian tubules remove nitrogenous waste incl toxic alkaloids
  • Sequestration of plants toxins as non-toxic form in haemolymph or toxins, e.g. cardelonides in monarch butterfly and milkweed bugs
  • stored in cuticle, specialised glands or organs
  • selective force may be defence as insects = aposematic
  • specific transporters allow insect to control where and when toxins accumulate
  • certain herbivores possess specific enzymes to boost bioactivity of the sequestered toxins
  • behavioural deactivation + avoidance - mass attack, vein cutting
  • host-plant location - allelochemicals used as oviposition or feeding stimulants, used to identify weaker plants
21
Q

Effects of herbivory on Ecosystem Services
- direct and indirect effects on nutrient cycling via:

A
  1. changes in carbon storage
    - induction of leaf fall, production of honeydew, defoliation
  2. Plant-plant competition
    - influence competitive interactions and affect plant composition
  3. plant resource allocation
    - allocation to root, shoot, seed, or flowers changes after attack
  4. alteration of food webs
    - impacts microbial and mycorrhizal interactions
22
Q

Effects of herbivory on Ecosystem Services
- decomposition and soil formation affected via:

A
  1. available resources
    - quantity and quality of dead/decaying plants entering soils depends on plant species present
    - above-ground consumers can affect decomposer communities and plant nutrients available
  2. effects on leaf litter quality
    - herbivory increases chemical defences which may persist in litter and affect rates of decomposition
23
Q

Effects of herbivory on Ecosystem Services
- Carbon and nitrogen cycling via - termites and ants

A
  1. increasing sa for microbial attack
  2. methane and carbon dioxide
    - termites can recycle carbon (as CO2 and methane) to atmosphere via gut microbes
  3. Nitrogen and Phosphorus
    - insects play a key role in cycling nitrogen via consumption
    - most plant communities occur where there are low levels available nutrients

Entomology (12 decks)

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