- Terminal Weevils - Biology
- making links & seeing the big picture
- make connections
- btwn "new" material and ..
- "current knowledge"
- your own knowledge base
- prev. lectures
- I'll model much of this in this lecture
- sometimes obvious (relevant)
- sometimes "off the wall"
- aim to get a B ... and you might just get an A
- "memorizing the details" vs. "big picture thinking"
- your choice
- "brute force" vs. "strategic"
- sometimes I make the big picture obvious ...
- big picture 1st ...
- understanding the "critical bits" of insect - tree interaction
- ... helps to "reason out" the mgmt
- pay attention to font
- important stuff (= "skull & crossbones")
- supporting stuff
- (interesting?) side stuff - little need to record
- greyed out - not covered this year
- General Overview
- coleoptera ...
- general life cycle
- egg --> adult: 1 or 2 years
- adults live ~4yrs
- damage
- kills leader ...
- ... growth loss
- mgmt
- hazard rating
- long term: "good forestry"
- tree breeding
- Spruce Terminal Weevil IWS
- H&R
- a.k.a. white pine terminal weevil
- most serious native insect pest of S & P regen in Canada
- up to $500 million/year
- in BC infested tree typically has 15-25% vol. loss
- range
- in BC - interior & coast (but not QCI)
- tree
- Canada - spruces & pines
- BC - Ss, Sx
- size: 2-10m (1.5 - 20m)
- age: 10-30 yr (5-40yr)
- dominant trees with large leaders
- 'history'
- natural stand - Ss is usu. minor
- S likes rich sites
- regenerates in openings with brush
- ... shade ... cooler, leader is obscured, smaller leaders
- IWS is relatively rare insect in natural coastal forest
- 60's-70's - large clearcuts ... plantations
- Biology
- Pissodes strobi, once considered 3 spp (Ss, Sx, Pw)
-
- adults emerge from OW in early spring
- walk/ fly to nearby tree
- young females
- feed to mature ovaries = maturation feeding
- then attract the males
- only mate once
- feeding - egg - fecal cap on leader below bud in spring
- lay "enough eggs"
- too few, young die - resin
- enough (~120) to overcome tree defense
- too many ... competition
- adults
- daily trip up/down tree (sleeps in duff)
- stay on sunny side of tree (E am - S noon - W pm)
- larva
- L1 feed independently
- most adults emerge late summer
- feed on laterals ... not damaging
- OW in duff below tree
- live 1-4 yrs
- spring: attack different tree (80% attack <5m)
- outbreak is considered 'localized'
- pop'n dynamics
- stabilized peak from 5-30 years (2-10m)
- outbreak intensity higher on better sites
- 25-50% of leaders attacked annually
- fluctuations due to weather, PPP
- then declines ...
- leaders smaller (inter-tree competition)
- "acquired defences" of tree
- Susceptibility Factors
- warmth
- leader size
- % S
- mortality factors
- up to 85% of larva (much less for adults)
- resin
- consituent resin
- induced resin
- competition (too many eggs)
-
- dipteran predator (Lonchaea corticis) is important
- brachonids parasitoids at low levels
- most effective at endemic levels
- not effective pop'n control in outbreak
- consider introducing parasitoids from Europe
- weather
- host selection
- attraction to host tree
- visual - silhouette, then ...
- ... chemical attractants / lack of repellants
- preference / antixenosis
- resin canal abundance
- pot'l antibiosis
- needle density
- assess nutritional value
- female attracted to tree - kairomones (vs. allomones)
- male attracted to female - pheromones
- S&S
- leader
- Damage
- deformity
- forks / crooks in "bottom log"
- in some cases may be minor
- avenue for decay
- restricted use of Ss on coast
- changing as resistant stock becomes more available
