Env. Resistance Nutrition, Biol. & Host

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)