APP203853: To release the parasitoid, Pauesia

nigrovaria, as a biological control agent for

Tuberolachnus salignus (the giant willow aphid) Stephanie Sopow, Scion; Barry Foster, Apiculture New Zealand; Dr Carl Wardhaugh, Scion

24 October 2019

Photo: osborn88

GWA Project Team:

Biology of giant willow aphid Tuberolachnus salignus (GWA)

Features:

• Largest known aphid (6 mm)

• Only females are known

• Live birth (no eggs)

• Can live for up to 3 months (cool

temps)

• Scarce in spring

In New Zealand since at least 2013

Host are willows, poplars, apples, pears…

widespread in NZ – both rural and urban

Stem feeder – ingests plant sap and

secretes honeydew – honeydew ‘rain’Photo: ‘shineybeetleman’

Impacts of GWA on apiculture in NZ

Barry Foster, Apiculture NZ

Impacts of giant willow aphid on

Apiculture

Barry Foster

Apiculture New Zealand

In support of submission

by Stephanie Sopow &

Carl Wardhaugh from

Scion on APP203853 to

release Pauesia

nigrovaria as a bio-

control of the giant

willow aphid

Impacts on bee health

Threat to critical spring pollen

and nectar supplies.

Willow found in most areas of

NZ – provides volume of

pollen for hive spring build up

Helps to build hives up for

pollination and honey flow.

Willow honey dew provides

carbohydrates for vespula

wasps which prey on hives in

autumn when the aphid and

vespula wasps are at their

maximum populations.

Impacts on bee products

Cement honey 30% loss or

more on extraction.

Clogged filters & process

equipment

Potential down grade mono

floral honey to honey dew

honey

Bees cannot digest melezitose

in willow honey dew

Willows as fundamental risk management tools

Stanley Braaksma, New Zealand Poplar and Willow Research Trust

Evidence of the direct impacts of GWA on willows

Stephanie Sopow (Scion) presenting the work of Dr Trevor Jones, Plant & Food Research

0 20 40 60 80 100

S. × fragilisS. matsudana × lasiandra

S. matsudana × albaS. matsudana × alba

S. matsudanaS. lasiandra

S. albaS. × reichardtii

S. viminalisS. schweriniiS. purpurea

S. lasiolepis × viminalisS. lasiolepis

S. eriocephalaS. candida

Percentage of trees

5 AprilAphid populations on unsprayed trees

Aphids >300 100-300 50-100 20-50 5-20 <5

Crack willow

Tangoio

Matsudana

Moutere

Kinuyanagi

Hiwinui

Booth

Holland

Irette

Glenmark

Aokautere

Viminalis

53%

25%

10%

6%

Willow clones

Willow poles supplied for soil conservation

Willow field trial at Massey University

Survival of willow trees after 2 years of

GWA infestation

0 20 40 60 80 100

S. × fragilis

S. matsudana × lasiandra

S. matsudana × alba

S. matsudana × alba

S. matsudana

S. lasiandra

S. alba

S. × reichardtii

S. viminalis

S. schwerinii

S. purpurea

S. lasiolepis × viminalis

S. lasiolepis

S. eriocephala

S. candida

Survival (%)No AphidsAphidsTreatment

Height growth of willows 2018-2019

0 50 100 150 200

S. × fragilis

S. matsudana × lasiandra

S. matsudana × alba

S. matsudana × alba

S. matsudana

S. lasiandra

S. alba

S. × reichardtii

S. viminalis

S. schwerinii

S. purpurea

S. lasiolepis × viminalis

S. lasiolepis

S. eriocephala

S. candida

Height growth (cm)

*

*

*

*

*

*

* Significant difference (p < 0.05)No AphidsAphidsTreatment

www.scionresearch.com

Scion is the trading name of the New Zealand Forest Research Institute Limited

Prosperity from trees Mai i te ngahere oranga

GWA caused reduction in height growth

GWA No GWA

GWA caused delayed spring flowering

GWANo GWA

GWA caused reduction in flower catkin size

healthyinfested

Not seen until spring of second year – willows gather and store

energy in autumn, but GWA siphoning off resources – infestation

is having a cumulative effect

GWA reduced above ground biomass to less than half that of the

controls after 9 weeks of infestation

GWA continued to influence the trees after the aphids were

removed – new shoots dehydrated

Dramatic reduction in root growth, and also decreased the mass of

previously developed woody tissue

Environmental and economic impacts of GWA in New Zealand

Stephanie Sopow, Scion

Direct and indirect effects of GWA

have numerous consequences Direct harm to host trees

Honeydew leads to poor bee health, bad honey

Sooty mould grows on honeydew coated surfaces

• Photosynthesis

• Fruit exports – kiwifruit

• Wool – sheltering sheep

• Nuisance

GWA honeydew is causing an increased abundance of vespid wasps

• Wasp expert Professor Phil Lester of Victoria University: “The rapid

spread of the invasive willow aphids, which have arrived in this

country in the past few years, have made the wasp problem even

worse than it would otherwise have been”.

The ‘bad wasps’ Bee killers & honey thieves

> 80,000 hives lost annually

Predators of native insects &

birds – affecting NZ’s biodiversity

Health risk

Now more widespread than ever

Experienced

honey losses

(of those that

saw crystals)

Chose to move

hives further

from willows to

avoid

crystalised

honey

Chose to

remove honey

early to avoid

issues with

crystalised

honey

Have seen

death of some

of these

willows

41%

Beekeeper survey results

Saw more

wasps robbing

hives &

predating on

bees

80%

Saw

crystalised

honey in the

comb

74%

50%

54%

80%

Have seen

blackened

stems or

branch

dieback of

willows

61%

Economic losses related to GWA

estimated at $300 million per year

Damage to willows & poplars (reduced root production

and overall biomass) – $145.8 m

• Reduction in mitigated erosion

• Carbon losses

Honey losses – $84.2 m

• Wasp impacts on production

• Wasp management costs

• Cement honey

Other wasp impacts – $64.4 m

• Reduced clover nitrogen fixation – wasps disrupting

pollination by interfering with bees

• Health costs and traffic accidents

Sooty mould – $5.5 m

• Kiwifruit losses

Dr Melissa Welsh

Estimated benefits of Pauesia nigrovaria Other species of Pauesia have been used as BCAs with great

success – e.g. black pine aphid in South Africa reduced number of

infested trees from 99% to 2% within 2-3 years after release of

Pauesia cinaravora

Simulations based on observations and best estimates of GWA and

P. nigrovaria fecundity suggest we could see a similar outcome in NZ

Modelled interaction between P. nigrovaria and GWA using methods

commonly used to model population growth and economic impacts

(simulations with and without P. nigrovaria to estimate its effect)

Predictions:

• 1% reduction in GWA in 1 month

• 34% after 1 year

• 80% once parasitoid ‘catches up’

Cumulative value of P. nigrovaria as a BCA

Mean value over a 20 year period = $1.5 billion

Selection of non-target aphid species for host testing

Dr Carl Wardhaugh, Scion

New Zealand Aphids – an overview of their

diversity and vulnerability to P. nigrovaria

Goal of host testing – to determine the potential vulnerability of non-

target aphid species, especially natives, to P. nigrovaria

Over 130 aphid species from 11 subfamilies established in NZ

But just 15 species are native, representing three subfamilies

~115 introduced pests of exotic plants

Used selection criteria recognised as best practice for classical

biological control, to select non-target aphid species for testing:

• Close relatives (the most likely to be attacked)

• Native species (representatives of native lineages)

• Similar size to target (GWA is large)

• Similar appearance (body shape, colour)

• Similar biology (attacks the arboreal parts of the same trees)

Giant Willow Aphid – Vital Statistics

The world’s largest aphid (5.8 mm long, and robust)

Attacks stems and branches of willows and poplars

Grey and black

A member of the subfamily Lachninae, the most primitive group of

aphids

• Since Lachninae branches early from the aphid family tree, they

are not closely-related to any other group of aphids

Aphid Phylogeny

An unrooted topology of the

family Aphididae. From

Novakova et al. (2003)

Pauesia nigrovaria – Vital Statistics

A member of the Braconid subfamily Aphidiinae

• All Aphidiinae wasps only attack aphids

Pauesia species are known to specialise on aphids in the subfamily

Lachninae

P. nigrovaria is only known to attack GWA in its native range

3-4 mm in length – much larger than any of NZ’s native aphid species

Host Selection – Lachninae

The subfamily to which GWA belongs

Represented in NZ by 8 introduced pest species

• 2 spp. on pines are very small (<2.5 mm)

• 5 Cinara spp. on cypress and juniper are larger (up to 4.5 mm),

attack stems, and are grey and black

• Selected species: Cinara fresai

− Widespread, large, Reared on Cupressus cuttings

− If P. nigrovaria attacks anything else, it should be this

Host Selection – Introduced Subfamilies

7 subfamilies contain no native species: Eriosomatinae,

Hormaphidinae, Saltusaphidinae, Phyllaphidinae, Calaphidinae,

Chaitophorinae, Drepanosiphinae

None attack willows or poplars

All are distantly related to GWA

Most are small (only 2 exceed 4 mm, and they are skinny)

Species selected - none

Sycamore aphid

(Drepanosiphinae)

Woolly beech aphid

(Phyllaphidinae)

Silver birch aphid

(Calaphidinae)

Host Selection – Neophyllaphinae

Represented in NZ by 2 endemic species (Neophyllaphis spp.)

Both feed on Totara (Podocarpus spp.)

Distantly related to GWA

Very small (2.2 mm)

Selected species – Neophyllaphis totarae

• Widespread

• Highly unlikely to be attacked

Host Selection – Taiwanaphidinae

Represented in NZ by 1 endemic species (Sensoriaphis nothofagi)

Feeds on the flush leaves of southern beeches (Fuscospora spp.)

Distantly related to GWA

Tiny (1.3 mm)

Selected species – Sensoriaphis nothofagi

• Widespread, but only occurs

when host trees flush

• Highly unlikely to be attacked

Host Selection – Aphidinae: Aphidini

A huge subfamily represented in NZ by two large tribes

Aphidini

• Represented in NZ by 11 endemic spp. and 16 introduced spp.

• Native species all feed on native plants, though GWA has been

recorded from a shared host plant (Coprosma robusta) of the

small (1.6 mm) native species Aphis coprosmae

• Distantly related to GWA

• All are small (<2.5 mm)

• Selected species – Aphis cottieri

− Widespread, but localised

− Reared on Muehlenbeckia

− Highly unlikely to be attacked

Host Selection – Aphidinae: Macrosiphini

Macrosiphini

• Represented in NZ by >60 introduced pest species, and 1

possible native species (Megoura stufkensi)

• M. stufkensi is small (2.5 mm), feeds on native broom

(Carmichaelia), and has not been seen since 2006

• Most introduced spp. are small, with just 3 exceeding 4 mm

• A few polyphagous species attack willows

• Selected species – Brachycaudus persicae

− Widespread, on Prunus

− A similar size (2.2 mm) to M. stufkensi

− Dark coloured, pear-shaped

− Highly unlikely to be attacked

Host Selection Summary

5 species selected:

Cinara fresai (large, closely-related to GWA, similar appearance)

Neophyllaphis totarae (endemic spp., small, distantly related)

Sensoriaphis nothofagi (endemic spp., small, distantly related)

Aphis cottieri (endemic spp., small, distantly related)

Brachycaudus persicae (representing the largest lineage and a

possible native, small, distantly related)

Represent our 3 native lineages, the largest lineage, and the closest

relatives to GWA

Relative sizes of aphids and P. nigrovaria

GWA

Neophyllaphis

totaraeSensoriaphis

nothofagi

Brachycaudus persicae

Aphis

cottieri

Cinara fresai

Proposed solution for long-term sustainable management of GWA

Stephanie Sopow, Scion

Options for control of GWA

Chemical control impractical, would put bees and other organisms at risk

Biological control

• Classical biological control: Using a natural enemy from the pest’s

place of origin (no suitable natural enemies found in NZ)

Unique situation in NZ makes this a good choice – geographic isolation,

gaps in certain taxa

Modern methods are robust – NZ a leader in biological control

Parasitoids a better choice than predators (generalists) or diseases (fussy)

Koinobiont endoparasitoids are ‘the bomb’ – greatest degree of host

specificity

Finding a candidate parasitoid

Looked for GWA in Japan and California – difficult to find

Collected and reared GWA in these countries to look for parasitoids

Found an excellent candidate in California – a koinobiont

endoparasitoid

Imported Pauesia nigrovaria from California in December 2017

Rearing in Scion’s containment facility GWA reared on willow cuttings

P. nigrovaria reared on GWA

Oviposition to adult: 16-21 days at 20°C

Average 8 offspring / day (GWA ~2)

Pauesia nigrovaria oviposition behaviour:

Host specificity testing No choice

Single mated female caged with 30 individuals of a test aphid species

for 24 hours

Reared aphids for one month, dissected remains

Tested viability of each female

Additional testing: behavioural assaysMated female Pauesia nigrovaria exposed to GWA or Cinara fresai, one at a time

for 5 minutes

0.033

Additional testing: behavioural assaysMated female Pauesia nigrovaria exposed to GWA or Brachycaudus persicae, one

at a time for 5 minutes

0.031 0

Conclusions

Pauesia nigrovaria appears highly

host-specific – unlikely to parasitize

any other aphids in New Zealand.

The greatest risk would be to close

relatives of GWA. In NZ all of these

are exotic pests – could be

considered an added benefit.

P. nigrovaria is expected to have the

indirect effect of lowering numbers of

pest wasps

P. nigrovaria will be screened for

bacteria and viruses prior to release

New 3 year Sustainable Food &

Fibre Futures project includes field

monitoring post release

Responses to submissions opposing the release of Pauesia nigrovaria

Stephanie Sopow, Scion

Response to Submission 127624

opposing the release of P. nigrovaria

This submitter expressed concern that an introduced wasp could harm

native insects and raised the point that historical cases have had

unintended consequences

Applicant response:

• The proposed BCA is not a vespid wasp, but a koinobiont

endoparasitoids – among the most host specific insects in the world,

having evolved to overcome the immune system of their hosts

• Unique case in NZ - native aphids very distantly related to GWA, and

much smaller in size

• Thorough host testing

• Modern processes for testing and approval much more rigorous than

they used to be

Response to Submission 127654 opposing the

release of P. nigrovaria

The submitter suggests that GWA feeds mostly on S. fragilis.

• R: The PFR study showed that at least 7 willow varieties commonly

planted in NZ are more susceptible than S. fragilis.

The submitter suggests that endemic ants could benefit from GWA and

that ants could interfere with P. nigrovaria’s ability to parasitise GWA.

• R: Very few observations of ant interactions with GWA have been

observed in NZ (student survey found primarily black house ant,

Ochetellus glaber - introduced). Any native ants would not be reliant

on GWA honeydew, since GWA is a newcomer. Volkl & Novak (1997)

found that foraging Pauesia pini laid more eggs into ant-attended

Cinara piceicola than into those unattended. They observed that P.

pini spent more time foraging where there were ants and that aphid

defence was reduced in the presence of ants. They speculated that

ants may help the parasitoid locate aphids and that the parasitoid

behaviour may be an evolutionary adaptation by the parasitoid to

gain protection from the ants against predators and hyperparasitoids.

Response to Submission 127654 opposing the

release of P. nigrovaria cont’d.

• R: The applicant would like to add that the abundance GWA

honeydew resource presents a risk for new invasive species to be

able to establish and proliferate in NZ, such as crazy ants (ex. 40

million red crabs wiped out on Christmas Island - now attempting

control by parasitoid of the scales that produce the honeydew)

The submitter suggests that the harlequin ladybird, Harmonia axyridis,

may provide the answer to controlling GWA in NZ.

• R: We acknowledge that harlequin ladybirds feed upon GWA, but

they are generalists that will feed on also on native insects and

displace native ladybirds. Harlequin ladybirds are known to be

serious pests overseas and decreasing GWA populations may assist

in lowering their numbers in NZ.

The submitter suggests that bees are infrequent feeders of honeydew.

• R: This is contrary to what we are observing in NZ, as evidenced in

by our beekeeping survey and the independent colony loss survey

conducted by Manaaki Whenua Landcare Research.

Response to Submission 127654 opposing the

release of P. nigrovaria cont’d.

The submitter suggests that other Pauesia may already be present in NZ.

• R: Ourselves and stakeholders have conducted numerous surveys

for GWA and we have not found any evidence of parasitism of GWA

in NZ. It is highly unlikely that any species of Pauesia are present,

given that they are known specialists of lachnine aphids, which are

not represented in the native fauna.

The submitter feels that this project comes with high risks.

• R: We disagree because Pauesia spp. specialise on lachnine aphids,

of which there are only a handful in NZ and all are exotic pests. The

chance of Pauesia nigrovaria evolving to parasitise another type of

aphid is extremely small. In order to do so, some would have to be

able to complete development within another type of aphid in order

for genetic selection to cause adaptation over time. This is highly

unlikely for a specialist koinobiont endoparasitoid.

www.scionresearch.com

Scion is the trading name of the New Zealand Forest Research Institute Limited

Prosperity from trees Mai i te ngahere oranga

Acknowledgements

WASP TACTICAL GROUP

Photo: William MetteyPhoto: William Mettey

Harlequin ladybird beetle, Harmonia axyridis Eats GWA but also a voracious predator of small native insects (aphids, scales,

psyllids… and other ladybirds), also outcompetes native ladybirds and transmits a

fungal disease

Feeds on fruit when other food becomes scarce

Can taint wine and cause allergic reactions

Photo: Mike Majerus

Reducing numbers of GWA

may in the long run to help to

reduce numbers of harlequin

ladybird