PowerPoint Presentation
The impact of volatile signals and cues on the behaviour of
aphids and their parasitoids Toby Bruce
Finding hosts in natural habitats:
Insects have evolved remarkable sensory abilities !
Volatile detection elicits behavioural responseThe nervous
system provides a simplified representation of the external
environment
but perhaps it is not that simple?
Jeanine Linz et al. Proc. R. Soc. B 2013;280:20130626
An insect can map a volatile in 4 dimensions: 3 dimensions of
space & fourth dimension of timeBetter sensing has a selective
advantage to enhance fitness finding mates & food
Split second decisions
Split second decisions
Insects have sharp spatio-temporal resolution of olfactory
signals
How a chemical is perceived depends on space & timeBruce et
al. (2005) TRENDS in Plant Science 10: 269
Chemical ecology methodsCollection of volatiles(headspace
sampling)
Bioassay (naturals)
GC linked electrophysiology
GC-MS identification of biologically relevant compounds
Bioassay (synthetics)Field testing (trapping experiments or plot
trials)
Two hypothesesSpecies-specific odour recognition: host plant
odour recognition relies upon taxonomically characteristic
volatiles not found in unrelated plant speciesORNPlant
VolatileCNS
ORNPlant VolatileCNS
Plant VolatilePlant VolatilePlant VolatilePlant
VolatileORNORNORNORN
Bruce et al. (2005) TRENDS in Plant Science 10:
269Ratio-specific odour recognition: plant odour specificity is
achieved by a particular ratio between constituent volatiles,
distributed generally among plant species
Attraction!Blend makes a difference
Webster et al. (2010) Animal Behaviour 79: 451
Insects have exquisite spatio-temporal resolution of olfactory
signals
Insects have exquisite spatio-temporal resolution of olfactory
signalsBruce & Pickett (2011) Phytochem. 72: 1605
Riffell et al. (2013) Science 339: 200-204Adaptability in a
changing environmentManduca sexta hawkmoths have innate preference
for night blooming flowers like jimsonweed
Adaptability in a changing environment !Switch to Agave palmeri
if there is a shortage
Detecting host qualityEAG active compounds: 2-pentadecanone,
2-heptanone, phenyl actetic acid, -gurjunene, 2-tridecanone,
-cedrene
Drakulic et al. (2015) Applied Environmental Microbiology 81:
3492Volatiles from Fusarium graminearum infested wheat are
repellent to grain aphid, Sitobion avenae
A short, sharp shock
Can crops be engineered to release alarm pheromone and repel
aphids and attract their enemies?
Aphid Alarm PheromoneAphid Alarm Pheromone
Naturally produced to warn other aphids when they are attacked
by a predator
Identified as (E)--farnesene for many economically important
aphids
Peppermint plants also naturally produce (E)--farnesene and the
gene responsible for its biosynthesis has been isolated.
Aphid Alarm Pheromone
transgenic linewild typeWheat transformed with targeted synthase
gene emits (E)--farnesene
Bruce et al. (2015) Nature Scientific Reports 5: 11183
Aphids repelled by volatiles of transformed wheatP = 0.010P <
0.001treatedtreatedcontrolcontrol
Parasitoid wasps spent longer foraging on transformed
plants*transgenic lineswild typeBruce et al. (2015) Nature
Scientific Reports 5: 11183
Pest Managementrepel pests
attract their enemies
Field trialField trialField trial
Long-term exposure
Bruce et al. (2015) Scientific reports 5: 11183
Same for parasitoids
Bruce et al. (2015) Nature Scientific Reports 5: 11183
Crop protection
The Challenge:
Can pest management become symbiotic?From an ecological and
evolutionary point of view, perhaps easier to work with beneficial
insects than against pest insects?
Challenging assumptionsInnate responses of insects to odors can
be exploited for pest management
but to what extent are responses innate?
should cues be associated with fitness?
https://thelifeofyourtime.wordpress.com/2011/11/13/plant-insect-interaction-parasitoid-wasps-on-goldenrod/
Biological control of pests - either by release in glasshouses
or encouraging natural populations outside.
Biocontrol in edible protected crops 2010/11 (UK)Aphidius ervi
used on 2072 ha: 350 ha tomatoes, 131 ha of cucumbers, 1511 ha of
peppers
Data from Fera Pesticide Usage survey (ha are treated hectares
and include repeat treatments)Aphidius colemani used on 3160 ha:
2235 ha peppers, 487 ha of cucumbers, 426 other vegetables
BiocontrolProven success in greenhouses with artificial
release
Conservation biocontrol strategies needed in outdoor cropping
environmentsGrowth rate and arrival rate slower than pestsCan
arrival be speeded up?
Conservation biocontrol - preserving what is already out
there
1= (E)--ocimene; 2= -terpinolene; 3= -caryophyllene; 4=
humulene; 5= (E)-4,8-dimethyl-1,3,7-nonatriene; 6= -cedrene; 7=
hexanal; 8= (E)-2-hexenal; 9= (Z)-3-hexen-1-ol; 10=
(Z)-3-hexen-1-yl acetate ; 11=
5,7,2,4-tetrahydroxy-6-(3-methylbut-2-enyl)isoflavanone (uncinanone
A); 12=
4,5-dihydro-5,2,4-trihydroxy-5-isopropenylfurano-(2,3;7,6)-isoflavanone
(uncinanone B); 13=
4,5-dihydro-2-methoxy-5,4-dihydroxy-5-isopropenylfurano-(2,3;7,6)-isoflavanone
(uncinanone C), and 14= di-C-glycosylflavone
6-C--L-arabinopyranosyl-8-C--D-glucopyranosylapigenin.
Khan et al. (1997) Nature 388: 631-632Khan et al. (2010) J. Exp.
Bot. 61: 4185
Classic example: Effective recruitment of biocontrol in
Push-pull
Volatiles from winter host repel summer forms1) 5-methylfurfural
2) 1-octen-3-ol 3) -pinene 4) chrysanthenone 5) methyl salicylate
6) cis-jasmone 7) caryophyllene 8) (E)--farnesene
cis-Jasmonecis-Jasmone
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cis-Jasmone
stress related volatile plant activator that induces defence
mechanismsbiological effects observed >24h after spraying plants
with cis-jasmone
Grain aphid Sitobion avenaeBiological effects (treated
wheat):volatile production changes and repels aphidsaphid
settlement is significantly reduced aphid growth and fecundity is
reducedaphid infestation is reduced in wheat field trialsaphid
parasitoids attracted to volatiles and forage longer
Arabidopsis :
Upregulated sequences OPR1/2Cell wall biosynthesis
genesCytochrome P450 (e.g. CYP81D11)F-box containing proteinNo
induction of:Defence genes (PR proteins, etc.)Stress genes (HSPs,
etc.)Jasmonate-regulated genes (OPR3, LOX)
Control cis-J meth-JSwitches on plant gene expression
cis-Jasmone
significantly longer time spent on induced plants
0510152025TreatedControlmin
Aphidius ervi foraging on cis-Jasmone treated wheat
Reduction in aphid numbers
Bruce et al. 2003 Pest Management Science 59 1031
Arabidopsis - Myzus persicae Aphidius erviBruce et al. 2008 PNAS
105: 4553-4558
cis-Jasmone upregulated sequences: OPR1/2 Cell wall biosynthetic
genes Cytochrome P450 (CYP81D11) F-box containing protein
Sequences unaffected by cis-jasmone: Defence genes (PR proteins,
etc) Stress genes (HSPs, etc) Jasmonate-regulated genes (OPR3,
LOX)Arabidopsis microarray analysis
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Aphidius ervi responses to CYP81D11 overexpressing plants
Bruce et al. 2008 PNAS 105: 4553-4558
Pheromone impact period
Aphid load reduced by half
Aphid load reduced by half
Pheromone impact period
JuneJulyAug
p
