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 ?