[APWG] NEWS: Biocontrol Insect Exacerbates Invasive Weed

[Todd Breitenfeldt]

I have been waiting a long time to answer to this thread as I collect my 
thoughts...  There is more to this evolving knapweed "story"...
------------------------
Biocontrol Insect Exacerbates Invasive Weed:
    This may be the case in some sights however, what we are seeing in 
many spots in SW Montana is that the knapweed seed head weevil Larinus 
minutus soon comes in and starts to infect a large percentage of the 
seed heads, displacing the gall flies.   These weevils are not present 
in the seed heads during winter (they overwinter as adults) so this 
decreases the mouse food source.  This is followed by Agapeta zoegana, 
the root boring moth which does not seem to usually kill the plant but 
may shorten its life span [both Larinus and Agapeta disperse well by 
flight].  Then if we follow up with the knapweed root boring weevils 
Cyphocleonus achates 
<http://mtwow.org/Cyphocleonus-achates-description.htm> (a very exciting 
bio-agent!), we finally are seeing spotted knapweed slowly decrease in 
density and in some sites in the Whitehall area and in other MT spots, 
almost completely disappear.  
http://mtwow.org/Biological_Control_Before_&_After.html 
<http://mtwow.org/Biological_Control_Before_&_After.html>
    Cypho. is a large flightless weevil that only attacks plants with a 
larger tap root (2-3+ yr. old plants).  Therefore, the effect we are 
seeing is that they knock out most of the larger/older plants in a few 
years and then it takes 8-12 years to use up most of the soil seed 
bank.  http://mtwow.org/Blue-Bird-Mine-Release-Site-sick-plants.html
    The seed head feeders take out most of the seeds, Agapeta weakens 
things and Cypho finish off the larger plants.  The sites will often go 
from many large knapweed plants to even more smaller plants [per square 
meter] as the seeds in the soil sprout after the large plants die, to a 
slowly decreasing density of knapweed as the native plants slowly come 
back as knapweed decreases....   
http://mtwow.org/Blue-Bird-Mine-release-site-views.html
    In MT places like the Bitterroot Valley So. of Missoula where 
knapweed has dominated for a very long time there is almost no native 
seed left so, cheat grass unfortunately often replaces the knapweed.  
Further E. in our area (between Butte and Bozeman) where the knapweed 
stands are younger and not as dense, we are seeing the natives able to 
come back in, as this 8-12 yr. process proceeds.
    This complex of insects seems to be what is needed and Cypho. are 
the crucial insect after the seed head feeders build up.
    We are mass rearing Cypho in insectaries at a number of MT and ID 
high schools.  The Ag. Experiment Station in Corvallis, MT started the 
insectary rearing of Cypho.  Because Cypho. do not fly we are busy being 
"Johnny weevil seed" all over the State.  
http://mtwow.org/insectary_ag_experiment_station_corvallis_mt_05.html
Cypho. pops. are building up nicely at many sites in MT.
 Whitehall insectary: http://mtwow.org/knapweed-insectary.htm

To conclude:  Biocontrol Insect Exacerbates Invasive Weed is a real 
effect however, I feel that it is short lived as the other bio-agents 
within the imported complex become established, this problem will go 
away, as will much of the spotted knapweed.

-most of the above statements are anecdotal...
-my personal goal is a release of Cypho. every 1/4 section where ever 
knapweed occurs.

Todd Breitenfeldt
Whitehall High School sci. teacher
Whitehall Biological Weed Control Project Coord.
http://mtwow.org/
---------------------------------------------------------------------------------------------

Olivia Kwong wrote:

> http://www.sciencedaily.com/releases/2008/09/080903134405.htm
>
> Biocontrol Insect Exacerbates Invasive Weed
>
> ScienceDaily (Sep. 5, 2008) -- Biocontrol agents, such as insects, are 
> often released outside of their native ranges to control invasive plants.
>
> But scientists in Montana have found that through complex community 
> interactions among deer mice, native plants and seeds, the presence of 
> an introduced fly may exacerbate the effects of the invasive plant it 
> was meant to control. The authors report their results in the 
> September issue of the journal Ecological Applications.
>
> See the link above for the full article text.
>
>
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