Nuclear Research Laboratory, Indian Agricultural Research Institute, New Delhi-110 012 (India).
*A part of approved Ph.D. Thesis submitted by H.P. Misra to the Post-graduate School, Indian Agricultural Research Institute, New Delhi (India).
The development of resistance in Tribolium castaneum (Herbst) to fenvalerate was investigated under laboratory conditions. From a parental stock with genetic heterogeneity, a strain resistant to fenvalerate was selected by continuous breeding in wheat flour treated with fenvalerate for seven successive generations maintaining a selection pressure above 60 per cent. Commencing with 50 ppm, the concentration of fenvalerate in the rearing medium was increased gradually in each subsequent generation reaching 2000 ppm in the 7th generation. Based on bioassay of 7 to 10-day old adults by topical application of fenvalerate, the LC50 value increased from 0.0217 in the parental to 0.0328, 0.0765, 0.0848, 0.3174, 0.5272, 0.5644 and 4.5720 per cent in the lst, 2nd, 3rd, 4th, 5th, 6th and 7th generation of selection, respectively. The degree of resistance was found to be 1.51, 3.52, 3.91, 14.63, 24.29, 26.01 and 210.69-fold for the 1st, 2nd, 3rd, 4th, 5th, 6th and 7th generations, respectively, when compared with the parental generation.
