Minutes of the 17th meeting held at PSD, York, Tuesday, 31st October, 2006
Collier, Rosemary (Warwick-HRI)
Denholm, Ian (Rothamsted Research, Chair)
Fenton, Brian (SCRI)
Foster, Steve (Rothamsted Research, Secretary)
McCaffery, Alan (Syngenta)
Mattock, Sue (Defra-PSD)
Meredith, Richard (Bayer CropScience)
Parker, Bill (ADAS)
Powell, Vivian (HDC)
Richardson, David (Defra-PSD)
Storer, Rob (BASF)
1. Welcome and apologies for absence
Rob Storer (BASF), Michael Tate (Syngenta-UK) and Juergen Langewald (BASF) were welcomed to the meeting.
Apologies for absence were received from:
Bean, Chris (UAP)
Hingley, Peter (Certis)
Walters, Keith (FERA)
2. Minutes of last meeting
The minutes of the last meeting were agreed.
The Resistance Risk Guidance Document passed to SM will be updated after the meeting.
Action: BP to update Guidelines on Resistance Management of M. persicae on Potatoes (before next meeting in April 2007)
There was no invited specialist speaker at today’s meeting as there was a full agenda.
IRAG minutes are also available from the home page
3. Feedback from Insecticide Resistance Action Committee (IRAC)
AMcC gave a presentation on current IRAC activities.
It has been very busy and significant strides have been taken over the last year. There are now seven different chemical companies involved. Sumitomo joined IRAC recently largely due to public health issues. However, Monsanto are still not a member despite IRAC being involved in biotechnology. The membership is still very biased towards the USA and Europe, and the group is attempting to address this.
IRAC has been re-organised into the following groups and teams:
- Functional Groups - Regulatory Liaison team, Communication and Education team.
- Expert Groups – Methods team, Mode of Action team, Biotechnology team, Public Heath team
- Project teams as required to address specific resistance issues.
In response to ID’s question of whether IRAC has a formal representative on the European and Mediterranean Plant Protection Organisation EPPO panel for resistance, AMcC said, there was. There will be a membership list on the website when it comes into action.
New teams have recently been formed to cover biotech and public health issues. With regard to the former, important gaps remain such as representation from China, where Bt cotton seems to be coming under threat from resistance.
In Google, IRAC comes first with the search words “insecticide resistance”. This is the result of considerable work on the IRAC website to ensure an optimum profile for the search engines.
The IRAC-run electronic publication, eConnection, welcomes short topical or technical contributions. Recently, these have been on brown plant hoppers, cotton whiteflies, and an SA-Link project (LK 0953) ‘Stewardship of Neonicotinoid Insecticides’.
IRAC’s Mode of Action classification scheme continues to be revised in light of the appearance of new molecules and new scientific data. However, this is increasingly being adopted as a definitive classification for supporting insecticide alternation strategies.
IRAC is continuing to update its list of approved bioassay methods and this now includes the glass vial assay for adult pollen beetles.
4. Regulatory Issues
DR gave a presentation on the ways that IRAC-UK can contribute to regulatory issues and a short history of PSD’s involvement in resistance risk assessment. Initially, there was no requirement to consider resistance in connection with regulatory issues. However, there is now a formal requirement to do this as part of the approval of new molecules and re-registration of existing ones for the UK marketplace. This will be based on the perceived risk of resistance, which depends on the mode of action, intended scale of usage and the proneness of target pests to evolve resistance. Assessment of risk will take into account factors such as the use of modifiers and restrictions on the number of applications, mixtures and different times of drilling (if it is a herbicide). Advice and restrictions will be communicated on product labels.
Monitoring any changes in target pests is judged to be important, particularly if the risk of resistance is considered to be high (e.g. for M. persicae), as waiting and responding to control failures may be too late. Groups like IRAG-UK can be used to solicit technical advice and consider whether action is necessary.
Companies may make specific applications for changes in approvals. PSD can make global changes if necessary, e.g. there has been a change in strobilurin labels. There is a need to encourage awareness of resistance through appropriate Resistance Action Groups (RAG) websites.
BP pointed out that a lot of this will be subjective and asked how much consistency there is across the board. DR replied by saying that PSD aims to be objective in their decisions. VP stressed that minor uses deserve special attention as some crops do not always have varied options for pesticide use. DR agreed that minor crops present special problems, but are considered on a case-by-case basis.
BF asked whether growers follow regulations. DR responded by saying that sometimes they do not, e.g. in the control of Septoria where PSD took the next step to restrict use in a statutory way to ensure that users follow the current rules.
RM said that supermarkets play a significant role in placing regulations on growers, which could undermine approvals by PSD and go against advice given by IRAG as their system is very much customer-driven. DR replied that supermarkets do have an influence and gave the example of Marks and Spencer giving a presentation where the whole objective was to supply produce that could be advertised as being “totally safe”. VP highlighted difficulties in establishing dialogue between Horticultural Development Council (HDC) and supermarket chains with respect to pesticide recommendations.
ID enquired about the remit and power of the new EPPO Permanent Panel on Resistance. DR replied that this is complicated as the European Commission (EC) does not have a culture of soliciting advice. However, EPPO would probably be the first ‘port of call’. Agrochemical companies have collective representation in Europe through the European Crop Protection Association (ECPA)and CropLife. No-one was fully clear about the differences between these organisations although CropLife probably has a wider remit.
4a. Restrictions on pymetrozine (SM and MT)
A background document had been circulated prior to the meeting to obtain IRAG’s opinions on pymetrozine usage and management. It had an off-label recommendation on brassicas, due to problems with Modified Acetylcholinesterase (MACE)-resistant Myzus persicae in 2003, but now has a full label. The question tabled by PSD was to whether usage recommendations for pymetrozine should follow those implemented for neonicotinoids on the same crops.
The discussion was informed by a presentation from AMcC providing Syngenta’s views on resistance management for Plenum WG in UK brassicas. Pymetrozine has a distinct (though unknown) mode of action and has been placed in Group 9B in IRAC’s classification scheme. The nearest similar compound in the classification is flonicamid, which is in Group 9C and is considered to have a different Modes of Action (MoA) despite also being a feeding blocker.
PSD’s assessment of resistance risk considers compounds with an unknown mode of action to be high risk because it is not possible to judge the potential resistance mechanisms that may evolve. However, a novel MoA is extremely valuable as target-site cross resistance is unlikely. Syngenta’s in-house data suggested that the cessation of feeding caused by pymetrozine is probably mediated by the serotonergic pathway and mechanoreceptors. Known detoxification and target-site mechanisms in aphids do not confer cross-resistance to pymetrozine. Pymetrozine therefore has an important role in resistance management in aphids. Furthermore, leaf-dip bioassays with pymetrozine have shown an intriguing slight but significant inverse relationship between EC50 and levels of E4/FE4 carboxylesterase over a wide range of M. persicae clones. It is not clear whether this relationship is due to biochemical differences or the result of pleiotropic effects on fitness/behaviour of the esterase mechanism.
Pymetrozine was launched in the UK in 1999 for controlling aphids in potatoes and has subsequently been applied mainly to control M. persicae. It is also approved for outdoor brassicas (cabbage, calabrese, cauliflower and Brussels sprouts). It gives excellent control of M .persicae and some control of Brevicoryne brassicae with Phase II seed oil adjuvant (which is not essential for M. persicae control). There is current on-label approval for two applications at 0.4 kg/ha. However, the original off-label use was approved for three applications.
Field experience suggests that optimum control with pymetrozine requires two sequential applications. Syngenta wished to allow growers the option of a third spray in some crops but the likelihood is that this will not be used frequently. The use of three applications will target two generations and provide greater flexibility.
In contrast to neonicotinoids, the overall exposure of UK M. persicae populations to pymetrozine has been low, and is likely to remain that way. If pymetrozine use is restricted, more pressure will be put on other compounds such as the neonicotinoids where there is significant variation in response to a level that confers low resistance. There is a markedly smaller area of the UK treated with pymetrozine compared to the neonicotinoids, partly because it has a relatively high price and has a rather specific and restricted target market. Pymetrozine has fewer approved uses on major crops. It has not been developed for use in sugar beet, oilseed rape, peas or beans and is not applied as a seed treatment.
The case for three applications was supported by VP on behalf of HDC, and there was a discussion of whether two split applications in rapid succession should be considered as one application or two from a resistance management standpoint.
DR thanked Syngenta and members of IRAG-UK for their contributions and will now consider their recommendation for use on brassicas.
4b. Pollen beetle resistance to pyrethroids- assessment of risks to the UK (DR)
DR presented a summary of current developments with pollen beetle resistance to pyrethroids in Europe and the implications for controlling this pest on oilseed rape in the UK. In 2003, there were reports of poor control of pollen beetles with pyrethroids in southern England but this was not substantiated in laboratory assays. In 2004, 26 UK samples of pollen beetles were tested at Rothamsted with no evidence of resistance to lambda-cyhalothrin. In 2006, four UK samples were tested by Udo Heimbach in Germany and again these proved to be susceptible. However, in 2006 there were serious control problems in Germany and resistance is now also known to be present in France, Sweden and Poland.
In the UK, the higher treatment thresholds (15/20 beetles per winter oilseed rape plant) and the generally low infestations in 2006 coupled with the fact that thiacloprid is also available as a foliar spray may be the reason why resistance is not widespread unlike in parts of Europe. If, and when, significant resistance is seen in the UK, will the problem have originated here or will it have been due to migration from continental Europe? What action, in the form of resistance management strategies, needs to be taken to avoid this?
AMcC presented results generated by Russ Slater at the resistance labs at Syngenta. An approximate chronology of resistance problems in pollen beetle is as follows:
- 1999 (Eastern France)
- 2000 and 2001 (France, Sweden)
- 2002 and 2003 (France, Germany, Switzerland, Denmark, Sweden)
- 2004 (France, Germany, Switzerland, Denmark, Sweden, Belgium, Poland)
- 2005 (most oilseed rape-growing regions of Europe, except UK and Austria).
Monitoring using the glass vial bioassay method has clearly shown the dramatic spread of resistance in Germany between 2001 and 2006. Field trials in the Schleswig-Holstein region of Germany showed that field efficacy correlated well with the vial data. UK samples were tested in 2006 from the seven counties with the highest oilseed rape acreage. Twenty one populations were assessed for resistance with the majority being susceptible or only slightly resistant. However, one population in Kent was strongly resistant.
ID showed slides provided by Ralf Nauen at Bayer CropScience showing very similar trends to those disclosed by Udo Heimbach and Syngenta. Ralf’s work also implicates enhanced activity of cytochrome P450-dependent monoxygenases as the primary mechanism of pyrethroid resistance.
BP asked if natural enemies were being lost because pollen beetle populations appeared to be so large. DR said that the application rate in the UK is higher than in mainland Europe. He also pointed out the potential impact of pyrethroid resistance on brassica production. RM said that Bayer CropScience will do some monitoring in the UK in 2007 but this will be for 10 samples at most as field staff are busy and beetles can be hard to find. There was a general consensus that all involved should use a standard methodology. Ralf’s experience is that the vial assay is not appropriate for thiacloprid and alternative method is required.
DR asked what IRAG should be recommending. ID suggested that we put out a short communication to alert UK growers giving them a point of contact. MT was less comfortable with this approach as we should not risk creating an atmosphere that might lead to claims of control failures based on potentially incorrect information. The situation in the UK is currently different to Germany where a span of only five years saw a small problem become very large. He thought that problems in the UK were likely to take 5-8 years as oilseed rape is not grown as intensely. We need to take actions to expand this timescale which will allow time to introduce new chemistry for pollen beetle control. This may mean label changes.
- Pyrethroid resistance affects all IRAC Group 3 compounds. Any regulatory action should therefore include all compounds in this group.
- Resistance is widespread in European oilseed rape, except the UK and Austria.
- Alternative insecticides are not ideal as Organophosphates (OPs) are on emergency registration only. Thiacloprid does not give the same level of control as OPs or pyrethroids (against susceptible insects), and resistance to neonicotinoids has been reported in Poland. However, there is some doubt over this report as the method used was developed for pyrethroids.
- Pyrethroids are currently effective in the majority of the UK but resistance must now be regarded as a severe threat. Pollen beetles are very mobile and could move into the UK from mainland Europe.
- It was concluded that an IRAG communication would be useful. This should be informative and frank, but not alarmist.
Action: ID to approach Home Grown Cereals Authority (HGCA) with the aim of putting together an IRAG-driven Factsheet.
4c. Continuing role of insecticide mixtures, resistance risks and regulatory implications (SM)
SM said that PSD are reviewing procedures for regulation of pesticide mixtures. There are indications of an increase in the number of pre-formulated mixtures being submitted for approval. There are number of issues at stake including the implications for resistance management and the fact that applying mixtures targeted against the same pest may conflict with a policy of pesticide minimisation. A number of these points were raised in a presentation by MT and some of the points are summarised as bullet points highlighted below:
The ideal situation for deploying mixtures would be:
- A cropping system where a range of pests occur together
- A combination of active ingredients (a.i.s) that target different pests with little or no overlap to provide a superior spectrum of control
- No existing resistance within the pest complex to either active ingredient a.i.
- Both a.i.s give a similar level of effectiveness against the various pests and have similar persistence of effect
- Both a.i.s are mixed at full rates
The advantages of mixtures are:
- They can provide broad-spectrum control of pests that occur at the same time in the crop
- Some mixtures may provide useful synergism
- They avoid the need to make tank mixes of separate products
- There is less risk of application rate errors thus increasing ease of use
- There is less packaging waste
- There are fewer tank partners
- There is the reduced potential for operator exposure
- There are fewer passes using less fuel and reduced labour costs resulting in lower costs to the grower
- They are more forgiving of pest ID errors
- They provide enhanced activity against specific pests through more than one mode of action
- There is less risk of resistance developing when two a.i.s are active against the same pest
- There is a greater predictability of control
- When one partner product is already compromised by widespread resistance, there can be strong selection pressure on the other.
- Potential for pesticide over-use.
ID said that it is important to distinguish between the pest control and resistance management elements of mixtures. There has been extensive modelling work centred around the concept of ‘redundant killing’ whereby the specific objective is to expose individual pests to full rates of two highly effective a.i.s in order to ensure that any insects resistant to one component are killed by exposure to the other. Redundant killing by definition entails applying a greater insecticide load than is necessary to effect control in the short-term. Since most mixtures are not developed with this objective in mind, the primary issue is really whether mixtures result in an enhanced resistance risk compared to compounds used singly.
The ensuing discussion touched on issues of timing if the occurrence of different pests is not synchronised, effects on beneficial organisms, the opportunities that mixtures provide for improving the versatility of existing molecules (especially in the light of a lack of a.i.s.
SM and DR closed the discussion by stating that PSD are drafting some guidelines on risk assessment for mixtures for consideration by the Advisory Committee on Pesticides ACP. The discussions had been helpful and PSD staff would report back developments at the next meeting.
4d. Update on Comparative Assessment (SM)
It seems certain that the principle of Comparative Assessment will be brought into the rewrite of Directive 91/414, and there is a need to consider implications for resistance management. The consultation on this rewrite is Regulatory Update 19/2006 entitled “Consultation on the Thematic Strategy for Pesticides: proposals for a Directive on the Sustainable Use of Pesticides and a regulation on Pesticide Authorisations”. This is on the website with a link from the homepage to 'Regulatory Updates Index'.
5. Update on Research
5.a. Defra/HDC funded project on aphid pests of lettuce and brassicas (RC)
RC presented results for 2006 from field experiments evaluating various active ingredients (including pirimicarb, pymetrozine, new a.i.s. and bio-pesticides) against several aphid species (M. persicae, Nasonovia ribisnigri and B. brassicae). RC is now aiming to write a Factsheet, produced jointly by HDC and IRAG, for resistance management in brassicas. However, this is complicated by frequent changes in the availability of insecticides and new products appearing on the market.
Action: RC to draft Guidelines on Resistance Management of M. persicae on lettuce and brassicas (before January 2007)
5.b. SA-Link project on stewardship of neonicotinoids (SF and ID)
SF reported progress with this project addressing the risks of M. persicae developing resistance to neonicotinoids. Two components of the project were presented:
(i) Screening live aphid samples collected from field and UK glasshouse populations (by staff from ADAS and Brooms Barn) for their response to imidacloprid. Samples collected since 2004 have been tested using topical bioassays applying a screening dose of 10 ppm imidacloprid. Fewer samples were collected in 2006 due to M. persicae being less common. However, these samples suggest there has not been a continued rise in the frequency of aphids showing low resistance to imidacloprid. Furthermore, there is still no evidence of the evolution of greater resistance that will cause control failures for neonicotinoids applied at doses aimed at aphids.
(ii) Over the last six months, several field-simulator experiments have examined how commercial seed treatments with imidacloprid in oilseed rape (OSR) and clothianidin in cabbage affect various components of fitness of two standard clones of M. persicae showing susceptibility and low-level resistance to neonicotinoids. These studies have provided a contrast, between the brassica treatment, targeted against aphids, and the oilseed rape treatment, aimed at Coleopteran pests. The experiments challenged aphids with plant/insecticide combinations that are currently present in the field. Measurements of feeding behaviour and fecundity were made at various periods after adult apterae were inoculated onto seed-treated and untreated plants (using small clip cages). The data show treated OSR has a small impact on M. persicae (after about two weeks) but this is not associated with neonicotinoid resistance phenotype. In contrast, treated cabbage had a major effect on both susceptible and resistant aphids although there appear to be some subtle advantages to aphids showing low neonicotinoid resistance.
5.c. SEERAD project on factors affecting M. persicae clones in Scotland (BF)
BF gave a presentation on the progress on a project looking at the genetic composition of M. persicae, primarily in Scotland. There appears to be very low genetic diversity in this species with predominant genotypes varying in abundance from year to year. In 2001, the predominant MACE-carrying genotypes were A and B. However, in 2003 and 2004 the MACE aphids were genotypes H and M.
Different genotypes transmit plant viruses at different proficiencies with genotype K (showing a dark-chocolate colour) appearing to be the best.
The reproductive rates of the newer MACE genotypes (H and M) are faster than the old MACE genotypes (A and B). These differences are more marked at low temperatures suggesting that they are more competitive under environmental conditions that prevail in Scotland.
SF summarised results of a Defra-PSD funded project assessing resistance to deltamethrin in UK onion thrips (Thrips tabaci). All samples looked at so far have shown resistance levels to deltamethrin that are similar to the high resistance published for onion thrips in New Zealand. As yet, no UK samples have shown responses equivalent to a susceptible New Zealand strain. It therefore appears that resistance to deltamethrin is widespread in the UK.
6. Proposal for a joint meeting of Resistance Action Groups (RAGs) and Resistance Action Committees (RACs) (ID)
Following the success of the Open Forum discussion at British Crop Protection Council (BCPC) 2005, Phil Russell has contacted ID asking if there could be a similar discussion for the RAGs and RACs at BCPC 2007. IRAC are keen for this to take place. IRAG members also thought this would be a good idea.
Action: ID to confirm the event with BCPC and oversee discussions on format.
7. IRAG outputs and review of forthcoming events
Resistance Management articles to be generated for pollen beetles and peach-potato aphids on potatoes and on brassicas.
Action: ID, BP and RC
8. Update on Resistance 2007
ID said that Resistance 2007 will be held at Rothamsted Research (16-18th April).
- The current status of resistance to pesticides
- Resistance mechanisms
- Population biology and modelling
- Applications of genomics
- Risk assessment and management
- Transgenic crops
There has been a great response in terms of offers of posters and talks, and these will be short-listed soon. IRAC International and Fungicide Resistance Action Group (FRAC) International will be meeting at Rothamsted in the same week in April. It would be good for IRAG to also meet during this time with the possibility of having a joint IRAG/IRAC session with a focus on the dissemination tactics of each and how the two bodies could work together more efficiently.
People can register their interest in attending by visiting the website: www.rothamsted.ac.uk/Research/Resistance2007.html
9. Any Other Business
Action: IRAG-UK members to decide on who will be invited to attend the next IRAG meeting to discuss resistance issues.
10. Date/venue of next meeting
The 18th meeting of IRAG-UK will take place on Thursday 19th April 2007 at Rothamsted Research in Harpenden. It will be hosted by Ian Denholm and Steve Foster. There will be a buffet lunch and an opportunity to meet IRAC and FRAC members.