Terminal Weevils ***biology Flashcards
Where do spruce terminal weevils overwinter and in what form
Over winters in the duff as an adult
Where does weevil lay eggs?
Lays eggs on leader (terminal) in the bark.
How long does it take for egg to mature to adult?
1 season. Adult lives for about 5 years relating the mating and egg laying cycle.
Lodgepole Pine weevil takes 2 seasons to mature
What is the damage?
Kills leader (repeatedly in outbreaks)
Deformity
Growth loss ***
Avenue for decay
Management
- hazard rating (warm climate helps weevil) weevil can’t build up in cold areas.
Survey
Short term: kill bug - Long term: happy healthy forest (plant brush space etc)
Tree breeding
Hosts and range of terminal weevil ?
IWS aka white pine terminal beetle - most serious native pasts of spruce and pine regen *** 40% volume loss in bc
Range: across Canada, not in cold areas
Where are spruce weevil a bigger problem?
Coast greater than interior
Warmer sites of vi and mainland bc
What trees are most affected?
Spruce and Pine
Bc - Ss Sx
Size preference: 2-10m (1.5-20m)
Age preference 10-30y (5-40)
Attacks dominants with good leaders
Are natural stands at risk?
Naturals at decreased risk because they do better underneath brush resulting in small leaders and wide spread stems.
Plantations at increased risk due to aggregation of food for weevil.
How many years of growth are killed when the weevils attack?
2
How far does the weevil typically travel
5m / yr
How often do females need to mate?
How many eggs?
1
Feed to mature ovaries
About 100 eggs per leader. Fecal pellet laid on egg to protect it
Why so many eggs per leader?
Need to be enough survivors to overcome tree defense
Where do adults prefer to be on the tree?
Wherever the sun hits
Sleeps in duff
What group does the terminal weevil belong to?
Coleoptera
How do the different larval stages feed?
L1 feed independently
L2-L4 in a ring
Downward to food. Kills 2 yr growth
How do larvae pupate?
Wood chip cocoons under bark
When do adults emerge and what do they do?
Emerge in late summer and feed on laterals
Spring, fly to attack new tree
What are some characteristics of the outbreak?***
Localized. When the stand is between 10-30 years and 2m-10m height the damage will be worst.
What things can reduce an outbreak?
Competition, weather, PPP
Why does outbreak decline after stand reaches 30-40
Once spruce is the dominant, it stops putting on fast growth and leaders are smaller
More effective resins produced as tree ages
Pop dynamic
Attack starts at 5 yr
Stable peak from 10-30 years
Outbreak local
Higher intensity on better sites
Susceptibility factors
Latitude, elevation and aspect (warmth)
Proximity to coast (maritime)
Why can BEC zones be used as a weevil guide
Weevil conforms to climate. BEC reflects climate
Stand preference based on *****
Host composition
2-10 m height 10-30 years age
Density (affects leader growth)
Crown closure and shading
Site productivity
Mortality factors
- resin response to feeding and oviposition ( constituent and induced )
Competition (too many survivors will result in not enough food)
PPP
Dipteran predators (not effective in outbreak)
Ground predation of sleeping adults by small mammals and other creatures
What is key for larva survival
Weather
Poor litter quality can kill OW adult.
Host selection ****
Beetle only lands on host spp (silhouette, chemical attractants, leader tip, needle density (less needles more sites), resin canal abundance, asses nutrient value)
Female attracted to tree, then attracts male.
S and S
Resin droplets - feeding punctures *
Black fecal caps on egg sites *
Larva - white 1 cm grub under bark *
Exit holes if ur late
Shepherds crook
Damage
10-40% reduction in merch volume
Avg 15-25
Dependant on: infestation level (20-40%) resident time (10-40 year)
What are some results of terminal weevil?
Restricted use of SS on coast
Changing as resistant stock is becoming more available.
