Abstract: Studies were conducted to ascertain the effect of the weather factors on incidence and development of H. armigera on different sunflower genotypes during 2008-2009. The H. armigera population was built up progressively from April 12 to April 27 in terms of egg count. The larval population started to increase continuously from April 12 to May 01 and a tremendous decrease was observed thereafter. The results reveal that maximum temperature during 2009 showed significant and positive correlation r-value of 0.514** with the egg counts of H. armigera. Whereas, on cumulative basis relative humidity and rainfall had negative and significant correlation with the eggs count with r-values of -0.525** and -0.479*, respectively. It is evident that a maximum larval population was recorded to be 5.64 per 5 plants on April 24, 2009. The determination of the effects of different weather factors on egg count and larval population of H. armigera in sunflower is essential for effective management of this pest.