The impact of low concentration fluoride on toxification was studied by treating $3^rd$ instar silkworm larvae of Qiufeng${ imes}$Baiyu (Fluoride resistant strain) and Jinshong${ imes}$Haoyue (Fluoride sensitive strain). The $5^th$ instar silkworm larvae of Zhenong-l, Shu-12, Qiufeng ${ imes}$ Baiyu, Chunhua ${ imes}$ Qhiushi, Jinshong and Haoyue were fed mulberry leaves treated with sodium fluoride at different concentrations to determine its effect on fecundity. Harmful effects of low concentration fluoride at early instars on growth, development and economic characters of Bombyx mori are related to its resistance. Harmful effect on resistant strain Qiufeng${ imes}$Baiyu manifested on prolongation of instar duration of 15 and 6% in 70 ppm, where as the sensitive breed Jinshong${ imes}$Haoyue manifested with 100% mortality in 50 ppm. The impact of low concentration fluoride on fecundity resulted in considerable increase in formed eggs (9%) and laid eggs (9%) in Zhenong-l and Shu-12 among treated population over control. The present observations emphasis that fluoride apart from exhibiting harmful effects on silkworm growth and development, however, its low concentration do playa vital role in inducing some positive effect on fecundity and cocoon traits.