author(s)
V Sunitha, TVK Singh, GB Supriya and J Satyanarayana

abstract
Insecticidal resistance studies against third instar larvae of DBM (Plutella xylostella L.) were carried out to know the rate of development of resistance from F₁ to F₃ generations in Delhi population. The third instar larvae obtained from field population were tested against acephate, cypermethrin, spinosad, cartap hydrochloride and Cry2Ab by using leaf dip method of bioassay to calculate LC₅₀ values. The LC₅₀ values of the insecticides were further used to quantify the resistance in P. xylostella of parental generation (F₀) from Delhi population. The survivals from F₀ generation were reared to next generation (F₁). Resistance development studies were carried out with third instar larvae of F₁ generation by applying a concentration of 80.00% mortality in every generation for selection from F₁ to F₃ generations against all the test insecticides and Cry2Ab toxin revealed that 1.27 folds resistance was developed against acephate in F₃ generation. In case of cypermethrin, 3.00 folds resistance in F₃ generation. Resistance studies further revealed development of 1.00 folds resistance against spinosad, 1.26 folds resistance against cartap hydrochloride, respectively, in F₃ generation of Delhi populations. In case of Cry2Ab toxin 1.35 folds resistance was recorded in F₃ generation. The rate of development of resistance from F₁ to F₃ generations increased in all the test insecticides and Cry toxin, except against spinosad from F₁ to F₃ generations.