Larvicide testing for blackfly control

Testing the blackfly organophosphate larvicide Abate® for viability in the Orange River Blackfly Control Programme

Industry Sector: Cattle And Small Stock

Research Focus Area: Animal Health and Welfare

Research Institute: University of KwaZulu-Natal

Researcher: Dr Nicholas Rivers-Moore PhD

Research Team:

Title Initials Surname Highest Qualification
Dr Helen Dallas PhD
Dr Robert Palmer PhD
Mr Shahin Naidoo BSc (Hons)
Ms Esther Ndou BSc (Hons)

Year of completion : 2017

Aims Of The Project

  • To confirm non-resistance to Abate in the Orange River pest blackfly populations;
  • To investigate the potential for re-activation of Abate as an alternative larvicide to Vectobac for control under high-flow conditions.

Executive Summary

Downstream flow alteration resulting from river impoundment or inter-basin transfer schemes, while improving water supply assurance levels, has been shown to have negative ecological consequences, including outbreaks in pest blackfly.  Outbreaks along the middle and lower Orange River have the potential to cause losses to livestock production estimated at US$13.3 million per annum (Rivers-Moore et al. 2014).  This figure is a conservative estimate as it excludes losses in the tourism and irrigated agricultural sectors through lost revenue and labour days.  Economic losses occur approximately 1200 km along the middle and lower reaches of the Orange River (Palmer 1997).  This is the river segment downstream of Van Der Kloof Dam, the major impoundment regulating flows in the Orange River.  The major pest species is Simulium chutteri, with more than 250 breeding sites (riffles) identified along the affected river sections, however S. damnosumS. nigritarse and S. adersi are also of concern (de Moor 1994, and citing others).

The Orange River Blackfly Control Programme, established in the early 1990s, was originally based on alternating use of two larvicides, viz. a bacterial larvicide (Vectobac®) and an organophosphate (Abate®; active ingredient is Temephos).  This programme extends over some 850 km of the middle and lower Orange River, where 148 rapids have been identified as optimal breeding habitat for pest blackfly species (Palmer et al. 2007).  The success of the control programme depends largely on correct timing of larvicide applications.  It is based on monitoring using a ten-point scoring system for larval and pupal densities developed by Palmer (1994), which is scientifically robust and user-friendly.  Larval density data are scored by the Department of Agriculture, Forestry and Fisheries (DAFF; Upington and De Aar regional offices) on a two-weekly basis, using the 10 point scale developed by Palmer (1994), reflecting seasonal changes of larval densities of the main blackfly pest complex comprising Simulium chutteri and S. damnosum.  The blackfly control programme along the middle and lower Orange River is based on aerial applications of larvicides to control the pest species Simulium chutteri.  Larvicides are generally applied three times in autumn and six times in spring (Palmer and Palmer 1995).  The two larvicides registered for blackfly control in South Africa are Vectobac® (produced from the naturally occurring bacteria Bacillus thuringiensis var. israelensis (Bti)and Abate® (organophosphate temephos) (Palmer and Palmer 1995).  However, wide scale application of the Abate larvicide, and blackfly larvae’s continuous exposure to it, has resulted in resistance being developed (Palmer and Palmer 1995).

Both larvicide options had advantages and drawbacks to their use.  In the case of Vectobac, the likelihood of pest blackfly developing resistance was low, but the higher viscosity and lower concentration of this larvicide in solution came with drawbacks including the need for more helicopter doses and clogging of nozzles.  While Abate does not result in these application drawbacks due to its more concentrated, lower viscosity formulation, its over-use was cautioned against because of the higher likelihood of resistance developing in Simulium chutteri.

By 2005, due to overuse of Abate, larvicidal resis been confirmed (Palmer et al. 2007), and a study completed in 2007 was unable to recommend any viable alternatives.  With ten years after the last use of Abate in the Orange River, it was hypothesized that larval resistance had diminished to the point where Abate could be used again.  During this period, where blackfly take 12-24 days to complete a life cycle, there is likely to have been at least 120-240 generations.  The purpose of this study was to establish whether blackfly larval resistance to Abate has subsided, thereby re-establishing a second larvicidal alternative for blackfly control on the Orange River.

Results

In the Great Fish River trials, larvae were a mixture of Simulium damnosum and S. chutteri in approximately a 3:1 ratio, while the reverse applied to pupae, and pupae dominated. Stock populations of blackfly larvae for the larvicide trials were low, with median values on the reeds sampled being 6.5 ± 1.4. Turbidity was relatively high, and flow rates were very low. Water was slightly alkaline, but with very high conductivity. In the Orange River, larvae were dominated by S. chutteri, with S. damnosum present, while pupal cases were almost exclusively S. damnosum with few S. chutteri present. Stock populations of blackfly larvae for the larvicide trials were higher than in the Great Fish River, with median values on the reeds sampled being 4.0 ± 1.4. Turbidity was relatively low, with prolific algal growth on rocks. Flow rates in the main river channel were normal; water was slightly alkaline, with conductivity comparable between river channel and irrigation canal.

Two concentrations of Abate were used: 0.3 mg.l-1 0.5 mg.l-1. Gutter trials of the efficacy of Abate on blackfly in the Great Fish River confirmed viability of the product, with mortalities of 95 and 97% respectively. Trials on Orange River populations showed similar trends at the same concentrations of larvicide. In all instances, declines in density classes were statistically significant (p < 0.05). In contrast, the class changes in the controls were not statistically significant (p < 0.05).

Conclusion

A downward change in density classes of blackfly larvae is expected to occur in both the control and trial gutter channels, due to a degree of downstream drift, where some larvae are dislodged and wash out of the gutters.  Despite this, there was a clear differentiation between changes in density scores between control sample populations and samples exposed to larvicide.  Not only was the viability of the Abate stocks confirmed after prolonged storage, but mortalities on the Orange River were significantly marked to indicate that larval resistance has subsided for concentrations of 0.3-0.5 mg.l-1.  In the project proposal, the original intention was to conduct larvicide trials on blackfly mortalities at a range of concentrations (0, 0.5, 1.0, 5.0 and 20.0 mg.l-1).  This range of concentrations was designed to range from the dosage concentration recommended by the manufacturers of Abate (0.10 ppm = 0.1 mg.l-1 or 30l per 100m3 where flows can be accurately determined), to higher concentrations to enable confirmation of larvicidal viability.  In this study, undertaking this full spectrum of trials was not possible due to the limited numbers of blackfly larvae available.  Additionally, it was demonstrated that Abate was effective at concentrations of 0.3-0.5 mg.l-1, which is within the magnitude of range recommended by the manufactures of Abate.

After a dormancy period of 10-15 years, blackfly larval resistance in the Orange River appears to no longer be a constraint in the use of Abate for blackfly control in the Orange River.

Objective Statement

  • Aim 1 (confirm non-resistance to Abate in the Orange River pest blackfly populations) has been successfully achieved.
  • Aim 2 (investigate the potential for re-activation of Abate as an alternative larvicide to Vectobac for control under high-flow conditions) will be an ongoing process. The Upington DAFF staff assisted with field trials. Further discussion will be required with DAFF (Upington and head office).

POPULAR ARTICLE

New hope for reintroduction of second larvicide to control muggies on the Orange River

Dr. Nick Rivers-Moore.

Red Meat Research and Development SA funded a recently completed study that tested a second larvicide for controlling pest blackfly on the middle and lower Orange River.  Mnr. Hoffie Joubert from KLK was also instrumental in assisting with project supplies.  While the larvicide is not new, it became ineffective in the mid-2000s for controlling pest blackfly here, because of a build-up of resistance to the product in the local blackfly population.  This means that only one larvicide, a bacterial larvicide called Vectobac, has been available for controlling blackfly for the past 10-15 years.  The Orange River Blackfly Control Programme, established in the early 1990s, was originally based on alternating use of two larvicides – a bacterial larvicide (Vectobac®) and an organophosphate (Abate®).  Both options had advantages and drawbacks to their use.  In the case of Vectobac, the likelihood of pest blackfly developing resistance was low, but the higher viscosity and lower concentration of this larvicide in solution came with drawbacks including the need for more helicopter doses, clogging of applicator nozzles.  While Abate does not result in these application drawbacks due to its more concentrated, lower viscosity formulation, its over-use was cautioned against because of the higher likelihood of resistance developing in Simulium chutteri.

By 2005, due to overuse of Abate, larvicidal resistance had been confirmed, and a study completed in 2007 was unable to recommend any viable alternatives.  With more than ten years after the last use of Abate in the Orange River, it was hypothesized that larval resistance had diminished to the point where Abate could be used again.  During this period, where blackfly take 12-24 days to complete a life cycle, there is likely to have been a few hundred generations, with resistance being bred out.

Dr Nick Rivers-Moore, an aquatic ecologist with fifteen years of research expertise on blackfly ecology, recently re-tested the efficacy of the larvicide Abate on pest blackfly.  This was first tested for product viability at a site about half an hour’s drive from Grahamstown on Great Fish River.  Here, the same species of blackfly which cause the outbreak problems on the Orange River have not been exposed to Abate.  Next, the gutter trials were repeated on the Orange River near Upington in the Northern Cape.  In all trials, larval mortalities were significant after application of the larvicide.  Dr Rivers-Moore said that “after a dormancy period of 10-15 years, blackfly larval resistance in the Orange River appears to no longer be a constraint in the use of Abate for blackfly control in the Orange River.”  These results were met with enthusiasm by the Blackfly Control Programme officers in the Upington DAFF office.  However, he says that “it is recommended that upscaling of these results is considered prior to re-introduction of Abate as a second larvicide for controlling pest blackfly on the Orange River.”

Please contact the Primary Researcher if you need a copy of the comprehensive report of this project –
Nicholas Rivers-Moore on blackfly1@vodamailcom

Nick Rivers-Moore

Blackfly outbreak predictive model

Development of a predictive management model for Orange River blackfly outbreaks

Industry Sector: Cattle And Small Stock

Research Focus Area: Animal Products, Quality and Value-adding

Research Institute: University of KwaZulu-Natal

Researcher: Dr Nicholas Rivers-Moore PhD

Research Team:

Title Initials Surname Highest Qualification
Dr Helen Dallas PhD
Dr Robert Palmer PhD
Mr Shahin Naidoo BSc (Hons)
Ms Esther Ndou BSc (Hons)

Year of completion : 2017

Aims Of The Project

  • To determine the amino acid profile of South African beef
  • To determine the validity of using nitrogen and a specific Jones factor to define protein quantity
  • To determine the protein quality of South African beef in the context of human nutrition

Executive Summary

Blackfly outbreaks on the Orange River impact on the agricultural sector through loss in conception, stock mortalities and loss in body weight gain, with losses of over R333 million pa. The Blackfly Control Programme has been in place for some twenty years, using a combination of bacterial and organophosphate applications at river breeding sites. This should have resulted in as many years worth of monitoring data, which, in analysis with flow data, would have provided a useful long-term dataset. Given acknowledged challenges, this has not been the case to the degree hoped for, with periodic outbreaks of blackfly continuing to occur, and the monitoring dataset being patchy and seldom evaluated. New thinking is needed that builds on existing research to reduce the chances of repeated outbreaks.

The aims of this study were threefold: to test and refine an existing Bayesian network predictive model of blackfly outbreaks; to undertake climate change scenario analyses to assist with future planning; and to provide an evaluation framework for blackfly monitoring data.

Fourteen sites between Douglas and Blouputs were monitored over four surveys: November 2015; March 2016; July 2016 and December 2016.

Data collected were blackfly samples (by species, density and relative abundances), hydraulic data (current velocities associated with multiple sample points per site), and water quality data (spot measurements of pH, conductivity, turbidity). Hourly air temperature data has been collected for 13 sites using Hobo TidBit data loggers, for 4 November 2015-5 December 2016. Water quality was fairly consistent between sites, but showed seasonal variation. Conductivity and pH had little impact on blackfly species patterns, with the exception of very high (> 1000μS.cm-1) conductivities in the irrigation return flow channels. Diatom data do, however, suggest that conductivities in the main Orange River have been increasing. Turbidity was a key driver in triggering ecosystem switching between dominance of pest blackfly species, and other blackfly species co-occurring with benthic algae.

Data confirm that the Orange River system switches between two states, viz. a high turbidity state favouring pest blackfly, and a clearer state favouring algal growth and where blackfly numbers are lower. Flow volumes and water temperatures affect turbidity levels, efficacy of larvicides, and availability of habitat for various ecosystem components (benthic algae, blackfly species). Thresholds were successfully identified from the abiotic-biotic relationships, which were incorporated into a Bayesian network model to predict the probability of blackfly outbreaks.

A predictive management framework was successfully constructed. An evaluation framework where ongoing monitoring by the Department of Agriculture, Forestry and Fisheries, and stakeholder involvement has been integrated through the development of a mobile phone App with an associated website. These are available through the Google Play App store (search for “Muggies”) and at www.muggies.org respectively. These also include links to two YouTube videos explaining how to download the App and to upload data, with explanations of the scoring systems. All data uploaded makes use of Google Pins, so that the data are geo-referenced. Model predictions are available to users.

Additional comments

A follow up article in Landbouweekblad has been confirmed with Landbouweekblad staff. Both MSc studies are due to be submitted in the next 1-3 months respectively. Two scientific papers from this research are currently being prepared for submission and review.

Objectives:

  • To test and refine the recently developed pilot probabilistic blackfly outbreak model by inclusion of temperature and turbidity data, and using previous flows and monitoring data
  • To undertake climate change scenario analyses to assist future management planning
  • To provide an evaluation framework for monitoring data of blackfly larval densities, based on the outbreak model

POPULAR ARTICLE

Boere wen oorlog teen muggies

Dr. Nick Rivers-Moore.

Boere in die omgewing van die Middelen Benede-Oranjerivier kan nou danksy tegnologie en ’n nuwe model help om muggie-uitbrekings beter te bestuur.

Met die selfoontoepassing Muggies kan enigiemand inligting deurgee wanneer groot getalle muggies in die 1 200 km van die Oranjerivier tussen Hopetown en Sendelingsdrif voorkom.

Die inligting sal saam met ander gereelde waarnemings deur die staat in ’n nuwe voorspellende bestuursmodel gebruik word om groot uitbrekings van muggies beter te kan bekamp. Die model, die toepassing en die webwerf www.muggies.org is in ’n navorsingsprojek ontwikkel wat in Julie vanjaar voltooi is. Die navorsing, onder leiding van dr. Nick Rivers-Moore, is deur die Waternavorsingskommissie (WNK) en die nasionale organisasie vir rooivleisnavorsing en -ontwikkeling (RMRDSA) gefinansier.

MUGGIESKADE

Die skade wat veeboere, spesifiek skaapboere, in dié gebiede aan die Oranjerivier ly, is sowat tien jaar gelede op minstens R300 miljoen per jaar geraam. Mnr. Hoffie Joubert, lid van Agri SA se nasionale waterkomitee belas met die uggieprobleem, sê dit is nou waarskynlik baie meer.

Luidens die jongste navorsingsverslag, Development of a Predictive Management Tool for Orange River Blackfly Outbreaks, kom verskeie muggiespesies in die gebied voor, maar dit is veral Simulium chutteri wat boere laat skade ly. Die ander spesies wat probleme veroorsaak, is S.damnosum, S. nigritarse en S. adersi. Volwasse wyfies van S. chutteri en S. damnosum voed op soogdiere se bloed, en laasgenoemde twee s’n op voëls.

Nick sê mannetjies vreet nek- tar en stuifmeel. Wyfies vreet ook hoofsaaklik nektar, maar het soos muskiete proteïen uit bloed nodig vir hul eiers om te ontwikkel. Dit is egter nie net skape en dus boere wat geraak word nie. Uitbrekings van muggies raak ook die toerismebedryf en inwoners van die omgewing. Die ergernisvlakke raak in ’n uitbreking van muggies so hoog dat werkers nie kan werk nie en toeriste sulke gebiede vermy. Luidens die verslag word die bestuur van die probleem bemoeilik omdat daar verskeie groepe met verskillende belange is, wat teen mekaar opgeweeg moet word. Ideale omstandighede vir groot uitbrekings hou onder meer verband met die volume water wat in die rivier vloei. Muggies hou van troebel water wat vinnig vloei. “Wanneer water stadiger vloei, is dit helderder. Water wat vinniger vloei, is troebeler. S. chutteri voed op sy doeltreffendste met watervloei van meer as 100 m per sekonde of ’n spoed van meer as 1 m/sekonde,” sê Nick.

Die vloei van die Oranjerivier het deur die jare aansienlik verander vanweë verskillende waterskemas, soos die Vanderkloofdam sedert 1977, die Gifkloofdam sedert 1971 en dan ook meer onlangs die Lesotho-Hooglandwaterprojek.
Veeboere verkies dalk ’n laer watervloei om uitbrekings van muggies te voorkom, maar besproeiingsboere met wingerd het meer water nodig, en Eskom het ’n bepaalde watervloei nodig om hidro-elektrisiteit op te wek.

Luidens die verslag moet ’n mens onthou dat hoewel muggies as ’n plaag beskou kan word, is dit ook ’n belangrike bron van voedsel vir baie roofdiere in die water is. “Die bestuursdoelwit behoort eerder die beheer as die uitwissing van muggies te wees.”

BEHEERPROGRAM

Die uitbrekings van muggies kom van tyd tot tyd voor. Die jongste een was in 2011 en voor dit in 2000-’01. Die staat het in die vroeë 1990’s met bestrydingsprogramme begin. Dit behels die toediening van ’n larwedoder vanuit ’n helikopter. Dit word gewoonlik drie keer in die herfs en ses keer in die lente toegedien. Twee middels is in Suid-Afrika vir die bestryding van muggies geregistreer: Vectobac® (reg.no. L7224, Wet 36/1947) en Abate® (reg.no. L2413). Opvolgnavorsing is onder meer tien jaar later gedoen om te kyk na alternatiewe larwedoders weens weerstandigheid by larwes teen temefos, ’n bestanddeel van Abate®.

Ondanks die bestrydingsprogram het uitbrekings steeds voorgekom, wat mense skepties laat raak het. Luidens die verslag hang die sukses van die program baie af van die korrekte tydsberekening van die toediening. Die redes vir die herhaalde en voortdurende uitbrekings is ingewikkeld. Dit sluit in hoër as normale watervloei in die winter, veranderinge in troebelheid, afwisseling van die oorheersende muggiespesie, larwedoderweerstandigheid en bestuurskwessies.

NUWE NAVORSING

Verskeie pogings is al aangewend om die voorkoms van uitbrekings te verminder, waaronder ’n geïntegreerde bestrydingsprogram en voortgesette monitering, ’n waarskynliksheidsmodel om te kan voorspel wanneer volwasse wyfies ’n groot ergernis kan wees, optimalisering van larwedodertoedienings en die skep van ’n advieskomitee. Nie een het die gewenste gevolge gehad nie. As deel van navorsing in 2014 is onder meer vasgestel dat die mees onlangse uitbrekings waarskynlik eerder aan bestuurskwessies as biologiese kwessies toegeskryf kan word. Verder taan belanghebbendes se belangstelling gewoonlik wanneer die probleem nie groot is nie, en verhoog eers weer wanneer daar ’n uitbreking is.
“Die probleem is tipies van die meeste plaagbestrydingsprogramme, en wys op die behoefte aan langtermyntoesig,” lui die verslag.

Die doelwitte van die jongste navorsing het ingesluit om ’n voorspellende model te ontwikkel, vir die eerste keer data oor troebelheid en watertemperatuur in te sluit, en ook te kyk na die moontlike invloed van klimaatsverandering. Alle vorige navorsingsinligting is wéér ontleed, maar dié keer saam met nuwe inligting wat in 2015 en 2016 ingesamel is. Dit het onder meer weeklikse troebelheidsen uurlikse watertemperatuurinligting ingesluit. Seisoenale insamelings van larwes en papies is ook in verskillende hidrolitiese biotope en habitatte gedoen om seisoenale veranderinge in die betreklik hoë voorkoms van verskillende muggiespesies te kan verstaan. Om die moontlike invloed van klimaatsverandering te kan bepaal, is inligting van die Universiteit van KwaZulu-Natal se departement hidrologie gebruik, wat aandui watervloei kan in die nabye toekoms 60% hoër wees.

BEVINDINGS

Die belangrikste bevindings van die jongste navorsing is: Die gehalte van water by die verskillende terreine was redelik dieselfde, maar het volgens seisoene gewissel. Die geleidingsvermoë van water en die pH-vlakke het ’n klein invloed op die patrone van muggiespesies gehad. Troebelheid was ’n sleutelrede vir ’n ander muggiespesie om die oorheersende een te word. Die water se vloeivolume en temperatuur het ’n invloed op troebelheidsvlakke, die doeltreffendheid van larwedoders en die beskikbaarheid van habitat vir verskeie ekostelsel-onderdele. Drempels is in die muggies se abiotiese-biotiese-verhoudings geïdentifiseer en in die model ingesluit waarmee die waarskynlikheid van uitbrekings van muggies voorspel kan word.

TOEKOMS

Vir die voorspellende bestuursraamwerk om suksesvol te wees, moet die insameling van inligting oor konsentrasies van muggies voortgaan. Inligting moet ook ingesamel word oor troebelheid en die voorkoms of afwesigheid van bentiese alge, wat verband hou met troebelheid. Al hierdie inligting moet, tesame met die lastigheidsindeks, op die webwerf gelaai word.
Die voorspellingsmodel moet dan met die inligting bygewerk en die verskillende data-onderdele moet van tyd tot tyd geoudit word. Wat egter ook baie belangrik is, is dat ’n “kampvegter” na vore moet tree, wat die raamwerk sal administreer en die maandelikse tariewe sal betaal vir die webwerf en die selfoontoepassing.

Die navorsers stel ook voor dat die ekonomiese invloed van muggies in die streek hersien word. Hoffie is opgewonde oor die bevindinge in die jongste navorsing en verwelkom die voorstel dat weer na die ekonomiese invloed gekyk word. “Inligting oor die omvang van die ekonomiese skade is belangrik vir die regverdiging van die toediening van larwedoder.” Hy sê die invloed van die gehalte van water op die toediening van middels moet ook nagevors word. Tans steun die plaagbestrydingsprogram net op die gebruik van Vectobac®, ’n organiese middel, weens die weerstand wat teen Abate®
ontwikkel het. Abate® het egter ’n baie groter reikafstand.

Hoffie sê die voorgeskrewe tydperk wat Abate® nie gebruik kon word nie, is nou verstreke en dit is belangrik dat dit weer getoets word. Agri Noord-Kaap gaan boere aan die rivier uitwys om die toepassing te gebruik om inligting oor muggies deur te gee en die organisasie sal dit monitor.

Please contact the Primary Researcher if you need a copy of the comprehensive report of this project –
Nicholas Rivers-Moore on blackfly1@vodamailcom