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Prospects for biocontrol of aquatic weeds in New Zealand

Prospects for biocontrol of aquatic weeds in New Zealand. Quentin Paynter & Paul Champion. History. In the past it was assumed that classical biocontrol of aquatic weeds was unlikely to succeed e.g.

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Prospects for biocontrol of aquatic weeds in New Zealand

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  1. Prospects for biocontrol of aquatic weeds in New Zealand Quentin Paynter & Paul Champion

  2. History • In the past it was assumed that classical biocontrol of aquatic weeds was unlikely to succeed e.g. • “It may be that… the relatively small numbers of species of plants & phytophagous insects, & perhaps the domination of this environment by fish, have caused in aquatic phytophagous insects a level of host specialization much lower than occurs in the species-rich terrestrial environment”1 • “Aquatic ecologists have noted that the diversity of the ingested food greatly exceeds the diversity of the aquatic insects… the majority of species appear to be generalists (polyphagous) rather than specialists (mono-or oligophagous)”2 1Wilson F 1964: The biological control of weeds. Annual Review of Entomology, 9, 225-244. 2Cummins KW 1973: Trophic relations of aquatic insects. Annual Review of Entomology, 18, 183-206.

  3. History • Since then a number of aquatic weeds have been targeted for biocontrol, with significant to spectacular impacts e.g. virtual 100% reduction of Salvinia molesta in Australia, South Africa & USA Lake Moondarra, Mt Isa, Queensland (Left = before; Right = after release of the weevil Cyrtobagous salviniae) [Photos: CSIRO] Room, P. M., et al. 1981: Successful biological control of the floating weed salvinia. Nature,294, 78-80.

  4. History • Eichhornia crassipes: Control by Neochetina spp. often excellent where the weed is not subjected to regular removal by periodic or annual flows, or mechanical & herbicide treatments1 • e.g. Kisumu Yacht Club Lake Victoria, Kenya June & December 1999, before & after biocontrol (Photos: CSIRO) 1Gassmann, A. et al. 2006: The potential for biological control of invasive alien aquatic weeds in Europe: a review. Macrophytes in Aquatic Ecosystems: From Biology to Management (ed K. Martens), pp. 217-222.Springer Netherlands.

  5. Hydrilla verticillata in the USA Hydrellia flies reduced Hydrilla biomass by 66% Grodowitz, M. J., et al. (2004) Hydrellia pakistanae and H. balciunasi, insect biological control agents of hydrilla: boon or bust? Proceedings of the XI International Symposium on Biological Control of Weeds (eds M. H. Julien, R. Sforza, M. C. Bon, H. C. Evans, P. E. Hatcher, H. L. Hinz & B. G. Rector), pp. 529-538.CSIRO Entomology, Canberra, Australia.

  6. Reappraisal! “Most herbivory on macrophytes is usually by specialized oligophagous herbivores” Newman RM 1991: Herbivory and detritivory on freshwater macrophytes by invertebrates: a review. J. N. Am. Benthol. Soc., 10, 89-114.

  7. Despite this, only 1 aquatic (alligator weed) targeted for classical biocontrol in NZ Agasicles hygrophila damage NZ Arcola malloi damage, NZ Effective on floating weed in warmer localities (ineffective in localities with terrestrial weed &/or winter frosts) Are there other potential aquatic weed targets in NZ?

  8. Ranking aquatic weed targets in NZ We used a recently developed scoring system to predict cost & success of biocontrol of 41 species of NZ aquatic weeds Paynter Q, Hill R; Bellgard S; Dawson M. 2009 Improving Targeting of Weed Biological Control Projects in Australia. Landcare Research Contract Report LC0809/072.

  9. SCORING SYSTEM Two main categories of factors used to rank feasibility of biocontrol: • Biocontrol ‘effort’ factors (how easy is a programme likely to be/how much will it cost?) • Biocontrol ‘impact’ factors (how big an impact is biocontrol likely to have?)

  10. ‘Effort’ scored according to 4 factors: • Target elsewhere. “Repeat” programs less effort vs. new programs - overseas surveys & most or all host-range testing is already done e.g. in NZ, average 53 vs 52 plant spp. used for host-range testing “repeat” & “novel” agents, respectively, but for repeat programmes an average of only c. 9/53 spp. tested in NZ • Plant phylogeny. Presence/absence of congeneric native/valued crop plants affects the complexity & duration [cost] of host-range testing • Accessibility & ease of working in native range. • Literature regarding natural enemies well known/accessible. e.g. UK fauna so well known, can prioritise candidate agents for many weeds from literature records alone

  11. Biocontrol impact: analytical approach • Searched biocontrol literature for quantitative information regarding: • Impact of biocontrol against weeds in Australia, South Africa & continental USA (long history of weed biocontrol) & • Plant traits of those weeds identified as hypothetically important determinants of biocontrol success

  12. Impact factors: analytical approach • Quantitative impact data collected in several ways (e.g. % cover; stems m-2; weed biomass) to allow comparison between weeds: • Data converted into proportions [dubbed the “Impact index” (I)] e.g.: If a weed density was reduced from 33 to 3.8 stems m-2 then: • Reduction in stem density = 3.8-33 = -29.2 stems m-2 • -29.2 • 33.0 • “Impact index” = • = -0.885

  13. Impact factors: analytical approach • If multiple data for a weed, an average was calculated unless data updated previous studies • If no biocontrol agents established or anecdotal reports of “negligible impact” biocontrol impact assumed to be zero, even if quantitative data lacking • Impact & trait data for 72 weed spp. • Impacts averaged for congeneric weed spp. with identical traits: reduced number of species/genera analysed to 57

  14. Plant traits correlated to biocontrol impact • Average biocontrol impact was lower on spp. recorded as weeds in the native range • & greater on spp. that reproduce vegetatively Bigger reduction/impact

  15. Plant traits correlated to biocontrol impact • Average impact was lower against terrestrial versus aquatic/wetland species • & greater against biennials/perennials versus annuals

  16. Developing a scoring systemfor biocontrol impact Score differentials for traits based on quantitative data (e.g. if average biocontrol impact was 2x higher for aquatic versus terrestrial weeds, it scored 2x more for that trait) Weighting of traits based on % variance explained in our analysis. Biocontrol feasibility score was scaled to add up to a maximum of 100 points. Assume that successes are repeatable, so a target that has been successfully controlled in another country automatically gets 100 points.

  17. Developing a scoring systemEcological feasibility Score < 50 Difficult targets: none achieved an impact index of -0.6 (but some got close) Score 50-70 Medium targets: 38% Impact index between -0.6 & -1 Score > 70 Good targets: 94% Impact index between -0.6 & -1

  18. Overall scoring • The best targets should be the most serious weeds • We excluded weeds targeted for eradication on a national level (unsuitable targets for biocontrol) • We used the Aquatic Weed Risk Assessment Model (AWRAM) scores1 for aquatic weed impacts 1 Biocontrol effort score Overall score = AWRAM score  Biocontrol impact  score 1Champion, P.D.; Clayton, J.S. (2000). Border control for potential aquatic weeds. Stage 1 Weed risk model. Science for Conservation 141. Department of Conservation, Wellington.

  19. Top ten NZ aquatic weed biocontrol targets

  20. Top 5: Lythrum salicaria • Wetland emergent (not strictly aquatic) from Europe • Somewhat limited distribution in NZ (AWRAM score may overstate current weed importance, but it is proving difficult to control using conventional means) • 81% reduction in weed biomass due to biocontrol in USA1 Galerucella calmariensis: Linda Wilson, University of Idaho, Bugwood.org 1Katovich, E. J. S., et al. 1999: Effect of Galerucella spp. on survival of purple loosestrife (Lythrum salicaria) roots and crowns. Weed Science,47, 360-365.

  21. Lagarosiphon major Native to South Africa Also a major weed in Ireland Recent collaboration between Irish & S. African scientists indicates Hydrellia flies & Bagous weevils attack lagarosiphon in S. Africa & are likely to be host-specific1 Host-range testing is already underway Photo: John Clayton; NIWA 1Baars, J. R., et al. (2010) Natural enemies from South Africa for biological control of Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae) in Europe. Hydrobiologia,656, 149-158.

  22. Egeria densa Native to South America Also a major weed in USA Recent native range surveys indicate promising agents exist including Hydrellia flies1 Host-range testing is already underway 1Cabrera Walsh, G. et al. 2007: Impact of the natural enemies on the potential damage of Hydrellia sp. (Diptera: Ephydridae) on Egeria densa. Proceedings of the XII International Symposium on Biological Control of Weeds, CAB International Wallingford, UK: 353 pp.

  23. Spartina spp. Native to Eastern USA (S. alterniflora) & Europe (S. anglica) Prokelisia marginata introduced from E. USA to west coast; invasive species on Spartina anglica in UK Preliminary results: 50% biomass reduction due to biocontrol in the USA1 Photograph: Chuan-Kai Ho 1 Grevstad, F. S. et al. 2003: Biological control of Spartina alterniflora in Willapa Bay, Washington using the planthopper Prokelisia marginata: agent specificity and early results. Biological Control,27, 32-42.

  24. Lysathia n. sp. reduced Myriophyllum aquaticum biomass by 60% in South Africa Cilliers, C. J. (1999) Lysathia n.sp. (Coleoptera: Chrysomelidae), a host-specific beetle for the control of the aquatic weed Myriophyllum aquaticum (Haloragaceae) in South Africa. Hydrobiologia,415, 271-276.

  25. Summary • Biocontrol has been overlooked as a means of controlling aquatic weeds in NZ • Recent developments indicate that some of the worst aquatic weeds in NZ are likely to be highly amenable to biocontrol • It is time NZ had an aquatic weeds biocontrol programme, like Australia, USA!

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