Refuge in bag: A smart strategy for outpacing bollworm resistance in Bt cotton

Transgenic crops expressing Bacillus thuringiensis (Bt) toxins effectively control major insect pests; however, the emergence of pest resistance can diminish their long-term effectiveness. The predominant strategy for delaying the progression of pest resistance to Bt crops boosts the survival of susceptible insects through “refuges” of host plants that do not produce cry toxins. Ideally, most of the resistant insects emerging from Bt crops will mate with the more abundant susceptible insects from nearby refuges. As Bt cotton has been widely adopted by Indian farmers since 2002, a proactive strategy was introduced to delay resistance to Bt proteins by planting 20 % of the field area with non-Bt cotton as a structured refuge. But to increase yields, farmers forego refuge planting. This reluctance resulted in short-term gains through increased yields but led the pink bollworm (PBW) to develop resistance to single-stacked gene Bt cotton by 2010 and to BGII by 2015. Thus, an extensive study assessing and comparing different refugia-in-bag (RIB) patterns for the bollworm complex, with special emphasis on PBW was conducted at Agricultural Research Station (ARS), Dharwad. Isogenic lines of Bt cotton hybrid (KCH-14K59 BG II) and its non-Bt were planted, following recommended agronomic practices. The pooled results indicated that the commercial RIB, fixed 5 % RIB, and fixed 10 % RIB treatments were statistically at par in terms of good boll opening (GBO), bad boll opening (BBO), and locule damage across all treatments. However, the highest seed cotton yield was recorded in T1 (13.45 q/ha), followed by T5 (12.37 q/ha) and T4 (11.78 q/ha), while the lowest yield was observed in T2 (6.62 q/ha). There was no infestation of Helicoverpa on Bt plants across the different treatments; however, PBW incidence and damage were predominant in all the blocks of both Bt and non-Bt plants.