Black bean aphid, Aphis fabae (Homoptera;Aphididae) is a serious pest causing crop loss. Plant-aphid interaction is a dynamic system subjected to continual variation and changes. Host plants induce various biochemical and physical defense mechanisms due to aphid feeding. Aphids can overcome plant defenses by enzymatic adaptations and sequestering secondary metabolites produced by the plant within their bodies as a defense against their enemies. Many strategies were developed and evolved by aphids in order to overcome plant defense barriers which allowed them to feed, grow and reproduce on their host plants. This study aimed to aid in better understanding of the effect of altering host plant on specialist and generalist aphid fitness.The influence of plant defense on population development of Aphis fabae was also investigated. Analyses for insect enzymes were also demonstrated in addition to further biochemical studies on host plant defences. Generalists showed different ecological and enzymatic adaptations towards host plants than specialist Aphis fabae. The results were fully discussed in details.