the mountain pine beetle: ideas on population dynamics & management in lodgepole pine

The Mountain Pine Beetle: Ideas on Population Dynamics & Management in

lodgepole pine

(1) I’ll review some of the basics of Dendroctonus ponderosae (MPB) as I go along.

(2) I’ll concentrate on MPB host selection behavior and barkbeetle management.

(3) I hope my thoughts will not crash: They’re new.

Whenyou’re lookingunder the barkof a dead pine, the MPBgalleries are sometimesdifficult to describe.

Important Review Topics:

1. MPBs have a sophisticated host selection scheme;

2. Populations disperse out of their host trees in spring and go into a down-

wind-random-dispersal flight;

3. Pioneering females find a weakened pine and expel a population-attracting

pheromone – cis-verbenol.

4. When the MPB attack density of a selected pine reaches a point where the

sexes are 50:50 the tree is no longer attractive. Why? At mating males

expel a masking pheromone – verbenone.

5. The switching mechanism takes over if the MPB population is high.

There are scattered susceptible lodgepolepines across the landscape – focus trees.

So let’s look at an endemic MPB population

The members of a low MPB population have the tough task of being able to find & colonize these scattered, water-stressed focus trees.

What they have is a super host-selection scheme.

Flying MPB Adults

MPB population isin a down-wind randomdispersal flight.

Susceptible pine (focus tree)

Pioneer

cis

-ver

be

no

l MPB populationnow flies up-wind in a concentratedflight.

Dispersal loss dropssignificantly.

Mass Attack

1st 2nd

Flying MPB Population

Susceptible pine (focus tree)

Pioneer

cis

-ver

be

no

l

1st 2nd

Random dispersal

Dispersalmortality is huge

Directedconcentration

Lowmortality

Dispersal flight:• Search the landscape for susceptible hosts – focus trees.• Mixes the gene pool and this is important: a period when the fittest are selected.• Provides a huge source of dispersal-mortality.

Concentration flight:• Provides a beacon to the formerly-dispersing beetles.• Ends a major source of population mortality. Even dumb beetles survive when their sense the aggregant.

Thoughts on Dispersal & Concentration Flights.

When the MPB population is low the host selection flight is desperately important in finding these scattered hosts.

Remember there are few scatteredfocus trees acrossthe landscape.

Few

MPB Latent Population

B.C.Long term drought pattern

200910yr October

Drought Index of NOAA

As a drought continues, more and more trees are stressed and more focus trees are created.

As more weakened trees are attacked, the higher goes the MPB population – exponentially!

“Once the population is high look out for the switching mechanism?”

When MPB population is high example

A focus tree is attracting males and females via the pheromone cis-verbenol produced by attacking females. Host volatiles also play a role in the bouquet of attraction.

But just at matingmales produce theanti-aggregant, verbenone.

Hours/minutes

Acc

um

ula

tive

atta

ck

Focus tree

Hundreds of males & females

attacking the focus tree

When thesexes arepaired

Time 1

Thetree is no longer attractive.

Time 2

Recipienttree

Time 3Neighboring tree is attacked

Spread of an MPB Spot in Lodgepole Pine: theswitching mechanism. The formerly concentrating

MPB, switch to the next largest tree(s)

F

R2

More spread of an MPB-Lpp Spot: the switching mechanism continues and beetles keep on picking-off the biggest recipient tree.

F1

R1

R2

R3

F2

R2

R3

In lodgepole pine, why do the MPBs switch attacks to the largest recipient trees?

The phloem of Lpp isthin! Whereas the phloemof ponderosa pine is thick.

During the first years of the outbreak the MPB population suffers “normal curve” mortality.

All 98.8% 69.9%

Tree DBH

% Mortality% Mortality Good SurvivalGood Survival

Fr

Why? Lodgepole pines have thin bark! The trees with small DBH have the thinnest phloem & highest brood mortality.

“…look at the variance.”

In lodgepole pine the MPBs that were concentrating on a focus tree switch their attacks to the next biggest recipient-tree. Ultimately they do a “diameter-limit cut.”

Switching mechanism (continued)

Meanwhile, the drought continues

(1) More and more focus trees & recipient trees are created: this increase is coupled with --

(2) Continuing use of the switching mechanism in host selection – less selection of the keenest beetles,

(3) Switching behavior signifies more and more brood trees are established & MPB populations go even higher.

The drought continues!

2015

Myriad of focus trees across the watersheds right at the time beetles start to emerge in

spring!

Early spring flight (…for whatever reason some emergefirst.)

Main spring flight

Time (days)

% E

mer

ge

nc

e

Flying Pop.

Freshly attacked trees are common since they were

infested by the small early emergence1.

Barley significant dispersal flight.

Cis

-ve

rbe

no

l

Massive generalspring emergence ispointed in the right directionand any tree is attacked.

1 Remember, lotsof focus trees.

There is synchrony between MPB emergence andattraction to new pheromone source.

There is no synchrony and MPB population dispersesuntil susceptible hosts are found.

Any Lpp

Susceptible Lpp

Concentration Dispersal PopulationLow High

Huge outbreaks have a synchrony between spring emergence and aggregating pheromone

No Dispersal Just Synchrony Between Emergence and Aggregants – Any Pine Is

Attacked

Can you all see that inbreeding is rampant?

So where have we been in this discussion?

Mountain Pine Beetle Outbreaks

Population Characteristics Host Selection Behavior Stand/Host Conditions

(1) Initial Phase

NormalDispersal flightsAggregant productionConcentration flightsBrood establishment

70-90 yrs old lodgepole – scattered drought stressed trees (focus trees)Stagnant growth (intra specific competition high) Fire exclusion for many yrsNo silvicultural treatmentsDrought conditions continue

(2) Tree to tree spread

NormalDispersal flightsAggregant productionConcentration flightsBrood establishmentSwitching behavior wide-spread

70-90 yr old trees in drought stressFocus trees wide-spreadNo fires and stand thinningsDrought continuesMassive stand mortality

(3) Population eruption

No dispersal flightsAggregants in synchrony with emergence commonAny tree attackedPopulation inbreeding occurs leading to population decline

All 70-90 yr old trees in drought stressFocus trees ubiquitousStand replacement fires possibleLandscape-wide pine mortalityPine regeneration begins across landscape after outbreak and fires

“…ok, from the top.”

(1) The Initial Phase of a MPB Outbreak

Host Selection

- Normal - Dispersal flights - Aggregants produced - Concentration flights - Broods established

Stand/Host Conditions

- 70-90 yr old Lpp, scattered drought stressed focus trees- Stagnant growth (intra specific competition high)- Fire exclusion for many yrs- No silvicultural treatments- Drought continues

Initial Phase

As a forest manager, now is the time to thin these stands!! Why? (1) to prevent the switching mechanism (2) to increase stand vigor and, ultimately, reduce numbers of focus trees and (3) to strategically use synthetic semiochemicals (attractants and repellants)

Distance between focus tree and recipient tree neededto prevent the switching mechanism.

(2) Rapid Tree to Tree Spread

Host Selection

- Normal - Dispersal flights - Aggregants produced - Concentration flights - Broods established - Switching behavior wide spread!

Stand/Host Conditions

- 70-90 yr old Lpp, scattered drought stressed focus trees- Stagnant growth (intra specific competition high)- Fire exclusion for many yrs- No silvicultural treatments- Drought continues- Massive stand mortality begins!- Massive MPB population explosion begins!

Rapid Spread Phase

What can you do?

(1) Worry about stand replacement fires,(2) Salvage for income and fire prevention,(3) Thin drastically those stands as yet un-infested(4) Forget the use of synthetic attractants or

repellents – big waste of money.

Synchrony of emergence & attraction begins – Wham!!

(3) MPB population eruption

Host Selection

- No dispersal flights

- Aggregants in synch withwith beetle emergence

- Any tree attacked

- Population inbreedingoccurs leading to populationdecline.

Stand/Host Conditions

- 70-90 yr old Lpp, focus trees ubiquitous

- Stand replacement fires common

- Drought probably continues

- Landscape mortality

- Pine regeneration begins across landscape after outbreaks and fires.

Eruption Phase

What can you do?

(1) Pray for good mkt. in forest products.

(2) Salvage

Don’t concern yourself aboutLpp – it’ll take off on its own.

Don’t worry about theMPB population, it’llcrash on it’s own.

1. Inbreeding2. Dumb beetles - few fat bodies

- poor responders- infertile

Why?

We’ve actually studied barkbeetles to prove that within any population there are dumb beetles.

Dumb Beetles for

Attractive bait (log with beetles imbedded)

Fan

Jar

One of a group of 3 olfactometers – used to collectattracted beetles: studies on Ips paraconfusus

05 25 45 etc.

Concentric release pts. of 05m – 2k m

…and we collectedbeetles from within anoutbreak and froman endemic area.

20

05

15

10

25

30

005 25 45 100 500 1K 2K

%R

eco

very

Distance to Olfactometer (m)

Beetles from endemic area

Beetles from outbreak area

Test to see if beetles from an endemic area werebetter responders to attractants.

Freshlyemerged

Caughtresponding

Emergence cage

Logs infested with beetles about to emerge.

Responding beetles

Emerging beetles

No. of re-runs

% R

eco

very

Responding beetles

Emerging beetles

No. of re-reruns

A test to shows that beetles who responded previouslywere better suited to find attractants

Highest Qual. Food

Lower Qual. Food

Low Qual. Food(Dry and fermenting)

Days

84 1612 20

% O

f L

og

s In

fest

ed

Lpp logs attacked by Ips spp. and quickly caged.

Release and response of barkbeetles that fed on high-qual. food.

Release and response of barkbeetles that fed on low-qual. food.

Release and response of barkbeetles that fed on awful-qual. food.

A test showing how food quality affects theability of barkbeetles to respond to attractants.

Some Conclusions on MPB PopulationDynamics

• When populations are latent, there is strong selection for the keenest beetles – strong flyers and response to host and pheromone plumes over long distances is the selection mechanism.

•There is a huge dispersal loss and only keenest survive.

• Population as well as individuals are tied in to the condition of the hosts – focus trees are stressed trees and many focus trees spells the beginning of population increase.

• Countless focus trees across the landscape ultimately eliminates the flight dispersal and selection of keen beetles as well as there is an increase in inbreeding -- all important causes of population collapse.

• Massive reduction in the quality of the MPB population and lack of host material is the end of the outbreak.

Outbreak collapse is due to lack of synchrony between spring emergence & response to volatile cues. Which, in turn, is due to lack of nearby susceptible host material.

Any Lpp

Susceptible Lpp

Concentration Dispersal PopulationLow High

• No hosts nearby• Pop. poor quality• Residual MPB pop. is seed corn for next latent pop.

Initial Phase of MPB build up

1. Thinning is mandatory before manyfocus trees are created. 2. Use of synthetic attractants andrepellents should be studied.

- confusion technique- push-pull studies- trapping

3. Bring back fire into the ecosystem.

As Forest Managers, What Do We Do?

Silvicultural studies in the South clearly show there is no control during the eruptive phase of a SPB outbreak.

Makes sense

Thinning southern pines

Thinning lodgepole pine

Bring fire back into the silviculturalequation

Well, I see it’s timeto quit.