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Collapse
Env. Resistance
Nutrition, Biol. & Host
Nutrition (of host tissue)
Quantity
food supply (e.g. MPB)
abundance contributed to outbreak
ate it all ...ultimate cause of collapse
Timing
"bumper" crops & seed pests
bud flush & defoliators
Biology (btwn organisms)
competition
only when resource in short supply
Bio-Control (3P)
pathogens
Bt
NPV
predators
parasitoids
hymenoptera (wasps)
diptera (flies)
Host Resistance
damage depends on host ...
host - pest interaction
attractiveness
defences
resilience
semiochemicals
= "signal chemical" .. "messengers"
pheromone
same species
examples
alarm (flight for aphids, aggression for ants/bees/wasps)
aggregation - general attractant
anti-aggregation
sex - "hey babe, this seat taken?"
path (food source -ants)
markers (seed insects "mark" egg sites)
allomone
produced by species A (tree) - affects species B (bug) behaviour - benefits A
generally "repellents" = - chemotaxis
kairomone
produced by species A (tree) - affects species B (bug) behaviour - benefits B
generally "attractants" = + chemotaxis
Host - Pest Interaction
a continuum
Preference (species, age, condition, or individual)
sight (silhouette or colour)
kairomone
alpha pinene - Fd beetle
ethanol - ambrosia beetle
terpentine - wood borers
Indifference
neither attractive nor repulsive
Antixenosis (non-preference, "repulsion")
= "against" "guest"
affects behaviour of the insect
repellants - no contact
deterrents - contact minimized
allomones
beta pinene repels Fd beetle
marigolds - volatile repellants
morphological
fine hairs
thick skin
surface waxes
Antibiosis
increased insect mortality, or ... reduced growth & reproductive success
toxins / growth inhibitors
jugulone toxic to gypsy moth
nicotine & pyrethrums = natural insecticides
Ss ... juvenile hormone
physical responses
"overgrowth" of tissue (e.g. BB gallery)
necrotic tissue surrounding eggs
resin - pitching out bark beetles
Resilience - Host Tolerance
withstand/ recover from the attack
still able to grow & reproduce
NOT insect-plant interaction - it's "recovery"
tree age & vigour
Evasion - Host PseudoTolerance
evades attack
but tree IS susceptible ... just got lucky
typically timing or rarity
susceptibility period short - shoot tip moths & terminal weevils - crown closure
out of sync - bud burst vs. egg hatching
isolated or rare tree spp. ... low pest pop'n (Ss, red pine)