A farmer leaves a part of the field with plants that do not make the toxin. What does this refuge do? (This topic is not in the NEET syllabus text.)

Fig. 1: The graph of the frequency of a resistance allele over generations with letters on the curves. Curve P rises fastest and reaches 0.5 near generation 59. Curve Q rises more slowly and reaches 0.5 near generation 324. A note says that one curve is for a crop with no refuge and the other for a crop with a refuge of 20 per cent of the area.