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Conservation biological control for the management of exotic forest pests
Hervé Jactel
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Conservation Biological Control: Definition
Pests can be biologically controlled by two ways. First, by importing exotic natural enemies that destroy pests = classical biological control Second, by conserving the native natural enemies of the pests that are already there or are readily available = conservation biological control
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Conservation Biological Control: Concept
Habitat manipulation to enhance native natural enemies So that they are sufficiently abundant and locally present to effectively control new pests By providing: - Alternate feeding resources: other prey (predators) or hosts (parasitoids) - Complementary feeding resources: pollen, nectar, honeydew (for adult parasitoids) - Shelter for protection against adverse weather conditions, super predators (spiders), hyper parasitoids, for egg-laying, overwintering
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Conservation Biological Control: Concept
The key condition: Native natural enemies need to be generalists enough to be able to shift onto the new (exotic) host or prey More likely to occur when the new host or prey belongs to same family or feeding guild as the native hosts or prey
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Conservation Biological Control: in agriculture
Flower strips
Intercropping
Beetles bank
Hedgerows
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Conservation Biological Control: in forest ?
Web of Science « conservation biological control » = 632 references « conservation biological control » AND « forest pest» = 1 reference
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Relevance for planted / plantation forests?
Ips grandicollis outbreak on Pinus radiata in Australia
Monocultures more invasible than mixed forests?
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Does tree diversity drive resistance to invasive forest insects?
= Conservation Biological Control in forest ?
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Diversity drives resistance to (native) forest pests
… but little evidence of resistance against non-native pests
2017
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Mechanisms? How does biodiversity confer associational resistance?
1. Diversity reduced abundance of host trees
2. Diversity reduces physical or chemical detectability of host
3. Diversity enhances activity of natural enemies of pests
• more insect predators, parasitoids, insectivorous birds
= conservation biological control mechanisms
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Two well studied invasive forest pests in Europe
Maritime pine bast scale Matsucoccus feytaudi
Asian chestnut gall wasp Dryocosmus kuriphilus
2012
2016
CABI
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Pure maritime pine stand Mixed stand of pines Pure black pine stand
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Chestnut Asian gall wasp Dryocosmus kuriphilus
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Crown damage assessment = % foliar loss
Explanatory variables
- tree species richness - proportion of chestnut trees / plot
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Results at the plot scale 100% of sampled chestnut trees attacked by D. kuriphilus. Foliar loss = 13 ± 8 % (0.8% - 31.1%)
Tree species richness
Me
an %
cro
wn
def
olia
tio
n p
er
plo
t P = 0.009
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Natural chestnut stands (Italy) • Monospecific CS • chestnut-oak CS-QC • chestnut-pine CS-PP • chestnut-ash CS-FO
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Torymus flavipes / oak galls
22 native parasitoid species
9 600 galls spring 809 parasitoids (mean: 8 per 100 galls)
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CONCLUSIONS
1. Promising results for conservation biological control of invasive forest pests with increased tree diversity
2. But we were lucky: similar hosts (two scale insects of the same genus, two gall makers of broadleaved trees) AND presence of generalist enemies able to shift onto new prey (predatory bug) or new host (parasitoid wasp)
3. More difficult cases = ex. Box tree moth (no native chewers)?
4. We need more research!
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Thank you for your attention
Inge van Halder ®