Fig. 2.

Thresholds for conditions causing increases or decreases in resistance based on a population genetic model. Table 1 gives empirical estimates of refuge percentage, fitness cost, and incomplete resistance for pink bollworm in Arizona. Incomplete resistance (I) indicates the fitness of homozygous resistant insects on Bt cotton relative to non-Bt cotton. For each of the four values of I examined (0.2, 0.4, 0.6, and 1.0), combinations of refuge percentage and fitness cost above each threshold line cause decreases in resistance, and those below each line cause increases in resistance. For example, with 50% refuges (close to the statewide mean) and I = 0.6, fitness costs of >37.5% cause decreased resistance, whereas fitness costs <37.5% cause increased resistance.