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Buddleia leaf weevil in New Zealand 5yrs on
Michelle Watson
OverviewOverview:
The weedbuddleia in forestryBuddleia in native forestsbiocontrol in forestry
The insect Field releases
what we found implications for forestry
Another biocontrol agent? How to collect and redistribute the agent
Buddleia (Buddleja davidii)
Woody shrub from China Rapidly colonises disturbed sites Fine, wind-dispersed seed Able to flower 1st yr, attain 4m in 2 yrs! Weed of plantation forests and natural areas
buddleia flower
Buddleia in forestry
Reduces growth of plantation species Number 1 weed central Nth Is. Difficult to control with chemicals Cost forestry industry ~$2.9 million/yr
control & lost production Buddleia control vital 3-5yrs after planting
Buddleia in forestry
1 yr old stand
Buddleia in native forests
Colonises disturbed sites = stream beds & slip sites
Alters plant communities, blocks access, shades rivers
e.g. Te Urewera, Kaikoura
Difficult to control due limited access
Buddleia biocontrol in forestry
Currently use herbicides to control buddleia But need to reduce chemical use (eg. FSC)
Challenge of an integrated control method: Must impact buddleia within 3 years of planting Weeds must be kept less than 60% crop height Large areas of buddleia need to be controlled Agent must be highly mobile to locate new sites
Buddleia leaf weevil (Cleopus japonicus)
Leaf feeding weevil from China Larvae most damaging stage Weevils lay 1-20 eggs per day Weevils readily fly First released in NZ in spring 2006
4mm
adult weevil larvae pupa
Field releases
1000 weevils released at 5 sites spring 2006 Tracked dispersal, damage and agent numbers
Established at all release sites Adults stop mating & laying eggs at high temps
no larvae January
Indicates do best moderate winter & summer
What we found?
February 2007 March 2008
Larvae present Sept to late May/early June Up to 95% defoliation in April 2008,’09, ’10 and ‘11 Heavy defoliation seen up to 5km from releases
What we found?
Other release sites
Further releases made
in areas where buddleia a pest
Councils, forestry, gold mine
2007-2011 ~ 40 releases
200-500 weevils per release
Distribution
*
Established at all release sites
Most new location records in Bay of Plenty
Dispersed over 50km from some release sites
Still lots of sites not colonised by weevil, would benefit from being spread by you
What we know about the agent:
Able heavily defoliate buddleia
Defoliation peaks in autumn
Repeated defoliation
Able to locate host plants further away - good adult flight ability
What we know about the agent:
Microclimate Preference for gullies Sunny, open areas
Often exhaust their resource – new adults forced to seek new host plants to survive winter
BUT, don’t know whether will colonise newly planted forests quickly enough, and impact
Buddleia with agent
Researching ability to colonise seedlings
Number larvae correlated with damage
Number of Cleopus japonicus larvae (no. plant-1)
0 5 10 15 20 25 30
Per
cent
age
defo
liatio
n (%
)
0
10
20
30
40
50
*Treatment level averages, by distance, for all days after release.
y = 10.62 x 0.33
R2 of 0.810
Time after planting (days)
0 100 200 300 400 500
Bud
dlej
a da
vidi
i hei
ght (
cm)
0
10
20
30
40
50
60
70
Buddleia height is reduced
End year 1= sig reduction in growth compared to insecticide-treated (control) plants
Treated plants
Untreated plants
Values - least square means & standard errors
Agent damage
Known that > 30% defoliation needed to effectively suppress buddleia in forestry
Created a model of feeding damage with distance
Predict that by end Year 1= plants at distance 0 will be more than 30% defoliated
Implications for forestry
What does this all mean?
Results indicate C. japonicus has the ability to suppress growth of buddleia seedlings
At first this is close to the source population
Repeated defoliation between & within yrs can be expected
Implications for forestry
Implications for buddleia biocontrol
Buddleia has amazing ability to re-grow following defoliation
At first responds by re-growing larger leaves Repeated defoliation needed to deplete plants
reserves Plant reserves depleted after second year defoliation = fewer flowers, less foliage, less height growth
Complimentary agent?
Is another agent needed?
• Mecysolobus erro = stem boring weevil
• Causes stems to wilt and die
• More host-testing needed
• Difficult to re-collect and rear
• May attack spring growth when cleopus is less effective?
Help spread this agent
Adults most robust life stage
Best collected in spring and autumn when easy to find
Collect by beating buddleia whilst holding a beat sheet, tarp, or upside-down umbrella underneath
Keep adults out of the sun in a ventilated container with buddleia stems
Release ~20-50 adults on a clump of plants
Contact Scion for advice on collection sites
Funding by FRST & Better Border Biosecurity (B3) program Forestry companies:
Rayonier, Hancock F.M., Timberlands, Pan Pac, Lake Taupo Forest Trust /NZ Forest Managers, Tempest & Associates Forestry, PF Olsen, et al.
The Conservation Company Jenny Dymock, Des Pooley Other forestry companies and Councils with releases Royal Society of NZ Scion Forest Protection group
Big thanks to…
Implications for forestry
C. japonicus will only be an economically successful buddleia control option in forestry if:disperses rapidly reduces growth of buddleia over entire standseffective within the first 3-5 yrs
However, benefits from buddleia control > 3yrs
easier for pruning & thinning roadside buddleia less vigorous reduced seed production ?
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