The present investigation were carried out on ‘‘Population dynamics on Mealy bug Phenacoccus solenopsis Tinsley and Thrips Thrips tabaci Lindeman on cotton’’ Field experiment was carried out at Department of Entomology, College of Agriculture, JAU, Junagadh during Kharif-2017. Incidence of mealy bug and thrips commenced in 29^th standard meteorological week i.e. 3^rd week of July month (0.2 mealy bug index) and (0.6 thrips/ 3 leaves). Population of Mealy bug index was gradually increased and attained a peak at 4.0 mealy bug index during 37^th SMW i.e. 2^nd week of September and second peak with 4.0 mealy bug index in 45^th SMW i.e. first week of November and remained constant up to 47^th standard meteorological week of November. When thrips population gradually increased and attained a peak at 30.5 thrips/3 leaves during 34^th standard meteorological week 3^rd week of August. Again, the thrips population increased and reached on second peak with 40.2 thrips/3 leaves in 36^th standard meteorological week i.e. first week of September. Thereafter, it started to decline slightly toward with 1.6 mealy bug index and 1.8 thrips/3 leaves during 51^th Standard meteorological week i.e. 3^rd week of December.

Among all the meteorological parameters, population of mealy bug showed highly significant positive correlation with bright sunshine hours (r = 0.714) and evapotranspiration (r = 0.622). Whereas, maximum temperature (r = 0.451) found significant positive correlation and population of thrips showed significant positive correlation with minimum temperature (r = 0.458) and maximum temperature (r =0.449)