Bt Brinjal The scope and adequacy of the GEAC environmental risk assessment

More documents

Recommendations

Info

42 Bt Brinjal: The GEAC environmental risk assessmentBFSB are not severe, then adoption of Bt brinjal is likely to be low, and there is a much lower risk of resistance. The proposededucation program will be designed to inform farmers that saving Bt brinjal seed will result in faster resistance evolution, andconsequently they should purchase new seed each year. It is not clear that saving seed will speed up resistance, but it is clearthat the education program will help increase seed sales.There are several approaches to resistance management in small-scale production systems in Vietnam that are discussed inFitt et al. (2008). These approaches should be considered in the context of Bt brinjal in India. One possibility is the use ofunstructured refuges, and another approach is to develop community-wide tactics.Finding 20. Event EE-1 Bt brinjal is a low dose event, which will require extra effort to manage effectively.Dose reflects the level of expression of the Bt transgene in the Bt plant and is either high or low (Box 11). The dose is notthe same as the efficacy or kill-rate of the Btplant, but it has an operational definition relatedto efficacy (Box 11). EC-II, the Dossier andthe Supplemental Materials make it clear thatthe present population of BFSB is susceptibleto Bt brinjal. Examination of the results fromthe small-scale field trials (Dossier, volume 6),indicates that efficacy of Bt brinjal varies from38% to 97% kill of the BFSB population, withan average of 73% kill and a standard deviationof 21%. This is far less than the concentrationneeded for a high dose event. Indeed, eventhe highest observed kill rate (97% kill) is lessthan a high dose event. Consequently, eventEE-1 is a low dose event. To be clear, the dataprovided in the Dossier (volume 6) contradictthe statement in the Dossier (volume 7) that Btbrinjal kills all BFSB larvae.Finding 21. Without any management ofresistance evolution, Bt brinjal is projectedto fail in 4-12 years. Effective use of 20%non-Bt refuges can extend this time by 25%or more.For the purpose of providing a roughanalysis of resistance risk and IRM, we simulatethe evolutionary process to project possibleevolutionary futures. To do this, we make thefollowing simplifying assumptions:a. BFSB is found feeding only on brinjal.As discussed above, BFSB may feed onwild and weedy relatives of brinjal, and ifit does and they are spatially intermixedwith brinjal, these could provide a naturalrefuge, and the time to failure would belonger than projected here. In addition,BOX 11High Dose and Low DoseThe dose of the insecticidal toxin in a Bt crop is a major factordetermining the level of resistance risk. Dose depends on both theconcentration of the toxin in the Bt plant and the genetic characteristicsof the target pest. Dose is a measure of the relative mortality of thethree possible genotypes associated with resistance evolution. Thesegenotypes are the RR homozygotes (with two resistance, R, alleles), the SShomozygotes (with two susceptibility, S, alleles), and the RS heterozygotes(with one of each kind of allele).A “high-dose” is defined as one that kills a high proportion (>95 %)of heterozygous resistance genotypes, so that the RS heterozygotes have asimilar mortality as the homozygous susceptible genotypes (Georghiou andTaylor 1977; Roush, 1997; Gould, 1998). In this case, resistance is saidto be recessive, and resistance evolution can be slow and can be delayedsubstantially.A “low-dose” is anything that is not a high-dose. If the mortalityof the RS heterozygote is similar to the RR homozygote, resistance issaid to be dominant, and resistance evolution can be extremely fast. Ifthe mortality of the RS heterozygote is between the SS homozygote andthe RR homozygote, resistance is said to be inermediate, and resistanceevolution can be fast.A provisional operational definition of “high-dose” is: a Bt plant thatexpresses Cry toxin at a concentration that is 25 times the concentrationto kill 99% of the target pest (Gould and Tabashnik, 1998). Analternative is at least 99.99 % mortality of homozygote susceptiblesrelative to a non-Bt control (ILSI, 1999). Caprio et al. (2000) found thatdominance and SS survival were correlated, such that higher SS survivalwas associated with higher dominance (low-dose). They showed that aconcentration of Cry toxin that is 50 times the concentration to kill 99%of the target pest is high enough that all known resistance alleles would befunctionally recessive (= high-dose).By any of these criteria, EE-1 Bt brinjal is a low dose event.
Environmental Risk Assessment 43non-Bt brinjal refuges will cause a greater delay in resistance than projected here.b. BFSB is the only species at risk of resistance evolution on Bt brinjal. If there are other species at risk, they should beanalysed as well to determine if they could be a more serious resistance risk.c. BFSB has evolved resistance to insecticides in India. The scientific documentation of this is thin, although it is widelystated. If BFSB has evolved resistance to insecticides then we can conclude that it has a population structure that wouldallow evolution to Bt brinjal as well.d. BFSB larvae can move from plant to plant, and fruit to fruit. This would imply that seed mixtures may speed up the rateof resistance evolution, and this IRM tactic might best be avoided.e. BFSB adults can move a few hundred meters and males and females are similarly dispersive. No published papers onadult movement could be found. The level of dispersal that is assumed is low relative to other species of Crambidae thatare pests in other crops. Given the small size of brinjal fields, this assumption means that most adults will leave the fieldthat they were born in (their natal field), but they will have little trouble finding another field (or returning to their natalfield). This leads us to assume that theproportion of adult males and females thatleave their natal field is 0.9 (r = 0.9). If r Figure 2. Time to failure of Bt brinjal for a. 50% adoption rate of Bt brinjaland b. 90% adoption rate. For each adoption rate, time to failure is shownwere lower, evolution would be delayed, but for heterozygosity (h) = 0.2 and 0.4, and for each of these heterozygosityif r were too low, evolution will speed up. values, time to failure is shown for four refuge options, no refuge (or nocompliance to the refuge), 5%, 10% and 20% refuge (assuming 100%f. All Bt brinjal have the same level ofcompliance). Failure time is the time until the R allele frequency reaches 0.5.control of BFSB (including any nonofficialseed). Heterogeneity in expression 0.9, s = 1, F = 100, a = 6, b = 0.8, p 0Simulations are based on the model of Alstad and Andow (1996) with r == 0.0001, K = 0.27, L = 1, and 3generations of BFSB on Bt brinjal per year. Other generations of BFSB areof Ccry1A could create hot spots where assumed to be on non-Bt plants during the rest of the year.evolution occurs very rapidly and spreadsto other areas. This would result in fasterresistance failures. Based on the survivalrates reported in the Dossier (volume 6), wecalculated the average survival on Bt brinjalto be 0.27, so K = 0.27.g. There is no fitness cost of resistance inBFSB (L = 1). A fitness cost of resistanceis defined as when the resistance genehas a lower fitness than the susceptibilitygene in the absence of selection forresistance. Thus, the resistance allelewould be favoured on Bt brinjal, but thesusceptibility allele would be favoured onany non-Bt host plant, such as the non-Btrefuge. Actually, a fitness cost is expected.Gassman et al. (2009) showed that nearly allBt resistance genes had some level of fitnesscost, however, it is not possible to predictthe fitness cost until resistance is discovered. Because the fitness cost varies from nil, which would have no influenceon resistance evolution, to large, which would greatly delay resistance if a refuge were used, we modelled no fitness cost.This is a worst-case assumption. If it turns out that BFSB resistance has a significant fitness cost, then the time to controlfailures would take longer to reach. More significantly, however, the use of effective 20% refuges would extend the time toresistance by much more than 25%.h. BFSB has as many as 8 generations a year (Alam et al 2003), but only three of them will be associated with Bt brinjal.
Page 1 and 2: Table of Contents 1Bt Brinjal Event
Page 3 and 4: Table of Contents iBt Brinjal:The s
Page 5 and 6: Summary and Conclusion 1Summary an
Page 7 and 8: Summary and Conclusion 3The EE-1 t
Page 9 and 10: Summary and Conclusion 5Event EE-1
Page 11 and 12: Summary and Conclusion 7Conclusion
Page 13 and 14: Context and Need 9standards for ER
Page 15 and 16: Context and Need 11and seek to incr
Page 17 and 18: Context and Need 13the reported yie
Page 19 and 20: Characterisation of Transgene 15Cha
Page 21 and 22: Characterisation of Transgene 17wor
Page 23 and 24: Characterisation of Transgene 19In
Page 25 and 26: Characterisation of Transgene 21Sci
Page 27 and 28: Environmental Risk Assessment 23Gen
Page 29: Environmental Risk Assessment 25thi
Page 32 and 33: 28 Bt Brinjal: The GEAC environmen
Page 84: Sunray HarvestersBungalow 69Mhow Ca

Bt Brinjal The scope and adequacy of the GEAC environmental risk assessment

Create successful ePaper yourself

Delete template?

Save as template?