Buddleia leaf weevil in New Zealand 5yrs on

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Buddleia leaf weevil in New Zealand 5yrs on
Michelle Watson
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Overview
Overview

• The weed
• buddleia in forestry
• Buddleia in native forests
• biocontrol in forestry
• The insect
• Field releases
• what we found
• implications for forestry
• Another biocontrol agent?
• How to collect and redistribute the agent

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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
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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

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Buddleia in forestry
1 yr old stand
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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

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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

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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
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Field releases

• 1000 weevils released at 5 sites spring 2006
• Tracked dispersal, damage and agent numbers

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What we found?

• Established at all release sites
• Adults stop mating laying eggs at high temps
  
• no larvae January
• Indicates do best moderate winter summer

February 2007
March 2008
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What we found?

• Larvae present Sept to late May/early June
• Up to 95 defoliation in April 2008,09, 10 and
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• Heavy defoliation seen up to 5km from releases

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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

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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

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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

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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, dont know whether will colonise newly
  planted forests quickly enough, and impact

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Buddleia with agent
Researching ability to colonise seedlings
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Number larvae correlated with damage
y 10.62 x 0.33 R2 of 0.810
Treatment level averages, by distance, for all
days after release.
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Buddleia height is reduced
End year 1 sig reduction in growth compared
to insecticide-treated (control) plants
Values - least square means standard errors
Treated plants Untreated plants
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Agent damage
Implications for forestry

• Known that gt 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

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What does this all mean?
Implications for forestry

• 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

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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

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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?

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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

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Big thanks to

• 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

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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 stands
• effective within the first 3-5 yrs
• However, benefits from buddleia control gt 3yrs
• easier for pruning thinning
• roadside buddleia less vigorous
• reduced seed production ?