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

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.