Effects of seed mixture sowing with transgenic Bt rice and its parental line on the population dynamics of target stemborers and leafrollers, and non-target planthoppers

The widespread planting of insect-resistant crops has caused a dramatic shift in agricultural landscapes, thus raising concerns about the potential impacts on both target and non-target pests. In this study, we examined the potential effects of intra-specific seed mixture sowing with transgenic Bt rice (Bt) and its parental non-transgenic line (Nt) (100% Bt rice [Bt(100)], 5% Nt+95% Bt [Nt(05)Bt(95)], 10% Nt+90% Bt [Nt(10)Bt(90)], 20% Nt+80% Bt [Nt(20)Bt(80)], 40% Nt+60% Bt [Nt(40)Bt(60)] and 100% Nt rice [Nt(100)]) on target and non-target pests in a 2-year field trial in southern China. The occurrence of target pests, Sesamia inferens, Chilo suppressalis and Cnaphalocrocis medinalis, decreased with the increased ratio of Bt rice, and the mixture ratios with more than 90% Bt rice (Bt(100) and Nt(05)Bt(95)) significantly increased the pest suppression efficiency, with the lowest occurrences of non-target planthoppers, Nilaparvata lugens and Sogatella furcifera in Nt(100) and Nt(05)Bt(95). Furthermore, there were no significant differences in 1000-grain dry weight and grain dry weight per 100 plants between Bt(100) and Nt(05)Bt(95). Seed mixture sowing of Bt rice with <= 10% (especially 5%) of its parent line was sufficient to overcome potential compliance issues that exist with the use of block or structured refuge to provide most effective control of both target and non-target pests without compromising the grain yield. It is also expected that the strategy of seed mixture sowing with transgenic Bt rice and the non-transgenic parental line would provide rice yield stability while decreasing the insecticide use frequency in rice production.