The present study aimed to investigate the effect of altering host plant on the mortality, Fitness and growth rate of the generalist and specialist aphids. 1.There was a significant increase in mortality of generalist aphids on Z. mays but low mortality on V. fabae. Mortality of specialist aphids was significantly low among V. fabae host plant and C. acutum. 2.The generalist aphids showed the highest fitness, growth rate and performance on V. fabae whereas specialist aphids showed lower fitness, growth rate and performance on V. fabae than on C. acutum. The generalist aphids took significantly different time to complete their development than specialists on V. fabae. 3. Biochemical plant secondary metabolites content among three aphid infested host plants The biochemical changes in plant secondary metabolites due to aphid infestation had been investigated. Host plant defence secondary metabolites differs from studied non host or toxic plants. The physiological changes in aphid enzymes among three different host plants had been investigated. Host plant alteration cause changes in enzymes activities between generalist aand specialist aphids.