Dilution of Resistance in Plutella xylostella L. to Different Insecticides

Laboratory studies on dilution of resistance by continuous inbreeding in successive generations of diamondback moth, Plutella xylostella to four commonly used insecticides viz fenvalerate, monocrotophos, quinalphos and cypermethrin revealed that there was a decline in resistance through generations to all the insecticides tested during 1998 and 1999 in Karsara (high insecticide input), Madaon (medium input) and Tikari (non or very low input) villages. The trend of dilution of resistance was erratic from F₁ to F₆ generations. In some cases, slightly higher level of resistance was observed in F₁ generation than the parent population. There was about 75% dilution in resistance in F₆ generation from the initial generation.