insect interactions - herbivory Flashcards
what is meant by the term ecosystem service
benefits from resources and processes which have been supplied by ecosystems
what is the UN2005 Millennium Ecosystem Assessment
an analysis of the state of Earths ecosystems and provides a summary and guidline for decision makers
list the ecosystem services which are split into four categories
1) provisioning
2) regulating
3) cultural
4) supporting
outline what is meant by the ecosystem service - provisioning
the production of food and water, raw material, medicinal resources and genetic resources
= products obtained from ecosystems
outline what is meant by the ecosystem service - Regulating
the control of climate and disease, purification of water, pollination, erosion and soil fertility, natural hazards regulation
= benefits obtained from regulation of ecosystem processes
outline what is meant by the ecosystem service - cultural
recreation and tourism, information and education, cultural heritage, mental wellbeing and aesthetic value
= non-material benefits obtained from ecosystems
outline what is meant by the ecosystem service - supporting
ecosystem process maintenance, biodiversity maintenance and protection, life cycle maintenance = underpins all other services
= services necessary for the production of all other ecosystem services e.g. primary production, soil formation and nutrient cycling
argued that time to put more effort into developing integrated research on the ecosystem services provided by insects as they may result in sustainable development goals
= provide evidence of ability to adress global challenges
= propose framework to shift perception of insects from enemies to allies and eventually soltions
what is an ecosystem function
something which maintains an ecosystem service including physiochemical and biological processes which occur in an ecosystem
= higher biodiversity stabilises and diversifies ecosystem functioning
= composition and diversity of functional traits which appear to be the best predictor of ecological processes
what is meant by a functional trait
morphological, physiological, phenological or behavioural characteristics of organisms which influence performance or fitness through effects on growth, reproduction and survival
outline how insects act as ecosystem service providers
they affect nutrient cycling both directly and indirectly
= reduce net primary production through herbivory and the breakdown of litter via detrivores
= important roles as ecosystem engineers
= indirectly –> may affect species composition
outline how insects can perform ecosystem functions via interactions with plants
interactions will have a signififcant effect on ecosystem functioning
= herbvivory and mutualisms (pollination)
give some examples of insect orders which are phytophagous (feed on plants)
- Orthoptera
- Phasmatodea
- Lepidoptera
- Coleoptera
- Thysanoptera
- Hemiptera
- Pscocoptera
- Hymenoptera
- Diptera
how are herbivorous insects categorised
- diet breadth = host plant range
= mono/oligo/polyphagous - feeding guild = chewers/sap feeders, free living/concealed
outline the category of herbivorous insects which are free-living chewers
eat exposed plant parts such as leaves, flowers or seeds
= most numerous mandibulate insects are coleoptera and lepidoptera (larvae)
Orthoptera, Hymenoptera and Phasmatodea
are next numerous
outline the category of herbivorous insects which are concealed chewers
include lepidoptera, coleoptera, diptera and hymenoptera
= lead tiers, rollers and miners feed internally between the upper and lower leaf epidermis
= wood and steam borers feed on bark, cambium, sapwood or heartwood of branches and trunks
= fruit and seed boers
= mandibulate herbivores also cause gall formations bu oviposition and feeding
outline the category of herbivorous insects which are free-living sap feeders
insects which insert stylets into various plant tissues
= phloem feeders e.g. aphids
= xylem feeders = cicadas, frog hoppers
= epidermis/mesophyll/parenchyma feeder = thrips, heteroptera
outline herbivory in the aquatic system
- 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 and small
bits of organic matter - Divided into gatherers (mayfly larvae) and
filter feeders (Blackfly larvae – Simuliidae)
how can insects use additional indirect injury during herbivory
salivary or other toxins may be injected that can cause infection e.g. european wood wasp injects venom into conifer hosts causing lethal fungal infections
= sap sucking and root/shoot feeders may increase transmission of viruses, bacteria and fungi
= HAS A BIG ECONOMIC SIGNIFICANCE
what are some ways plants defend themselves from herbivory
1) plant nuttrition = N and P limited
2) mechanical and structural barrier = toughness and hardness, trichomes and surface waxes
3) allelochemical barriers = secondary metabolites
outline how plant nutrition can be used to defend against herbivory
outline how mechanical and structural defences can be used to defend against herbivory
Toughness and 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 and
aid water and nutrient absorption
* Reduce oviposition, alter movement -> reduce
growth and fecundity
* Hooked trichomes cause injury to Lepidoptera
larvae leading to loss of haemolymph,
desiccation and deat
Surface waxes protect against
desiccation and pathogen invasion
* Slippery surface prevents attachment in
some Lepidoptera larvae and aphids
* Some herbivores can maintain
attachment, e.g. Phyllotreta cruciferae
* Interactions between surface wax
structure and tarsal morphology
prevents certain species attachin
how have insects evloved to counter mechanical plant defences
Relative head size of chewers of grasses (silica)
e.g. grasshoppers, caterpillars
* Extra moults to replace worn mandibles and chiseledged 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 with
tarsal pads
outline how allelochemical barriers can be used to defend against herbivory
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 and signalling
Allelochemical diversity → difficult to
categorise
* Qualitative / quantitative or toxins /
digestibility reducers
* Qualitative / toxins interfere with
metabolism, e.g:
* Alkaloids – Deadly nightshade (atropine),
tobacco (nicotine)
* Pyrethrins - chrysanthemum
* Cyanogenic compounds – Prunus sp
what is meant by volatile organic compounds
secondary metabolites which are emitted by plants as a consequence of interaction with biotic and abiotic factors
= very important role in plant evolution
= floral VOCs ofetn invloved in defence or pollination attraction
= act as repellents or for indirect defences such as attracting parasitoids or predators
how have insects evloved to overcome allelochemical barriers
- 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 including toxic alkaloids
Sequestration of plant 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 toxin
Behavioural
deactivation and
avoidance – mass
attack, vein cutting - Host-plant location –
allelochemicals used
as oviposition or
feeding stimulants,
used to identify
weaker plant
what are the effects of herbivory on ecosystem services on nutrient cycling
direct and indirect effects on nutrient cycling via
1) changes in carbon storage = induction of leaf fall, production of honey dew, defoliation
2) plant-plant comp - 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
what are the effects of herbivory on ecosystem services on decomposition and soil formation
- 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 - Effects on leaf litter quality
‒ Herbivory increases chemical defences which may
persist in litter and affect rates of decomposition
what are the effects of herbivory on ecosystem services on carbon and nitrogen cycling
o Termites and ants
1. Increasing surface area 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 nutrient
