Fitness costs and biological adaptability of Cry toxin-resistant field strains of Pink bollworm, Pectinophora Gossypiella (Saunders) from India

Pink bollworm strains (F₀) collected from 59 geographically different locations across India were advanced to F₁ and screened for Cry toxin resistance using 21-days diet incorporation bioassay. The survived population from five locations with the highest LC₅₀ values for Cry1Ac were grouped as highly resistant, while those from five locations with lower LC₅₀ values were grouped as relatively less resistant. Similarly, populations with high and relatively low resistance to Cry2Ab were also developed. Further, these populations advanced to next generation. One-day-old neonate larvae from all populations, along with a susceptible strain (F₁₉₄), were exposed to various selected doses to evaluate the precise impact of these concentrations on biological fitness. The results indicated that higher concentrations of Cry toxin prolonged the larval, pupal, and total developmental durations, while reducing adult longevity, fecundity, and egg hatchability. Egg incubation period, however, remained unaffected. Susceptible strains on toxin-free diet exhibited the shortest development times (larval: 18.48 ± 0.95 d; pupal: 7.22 ± 0.36 d; total: 39.41 ± 2.52 d), longest adult life (9.78 ± 0.35 d), highest fecundity (123.15 ± 4.95 eggs/female), and greatest survival rates (> 95%). Their growth (5.28) and survival indices (0.97) reflected robust development under non-stress conditions. Conversely, toxin exposure increased mortality and malformations, particularly in susceptible strains. Fitness costs due to Cry1Ac exposure were highest in susceptible strains (84.42% at 1.0 µg/ mL), followed by less resistant (79.46%) and highly resistant strains (60.07% at 10.0 µg/ mL). For Cry2Ab, the relatively less resistant strain showed the highest fitness cost (74.51%), followed by susceptible (58.82%) and highly resistant strains. Overall, fitness costs were closely linked to reduced fecundity, egg hatchability, larval survival, adult emergence, and prolonged development.