Despite the abundance of plant macronutrient, nitrogen in the environment, plants are unable to use it directly for their growth and development. In order to obtain nitrogen from the environment, Rhizobia, beneficial soil microbes forms symbiotic relationship with plant family, Fabaceae, by converting the atmospheric nitrogen to a usable form in the soil for plants to use it, and the microbes gets carbon nutrients in return, from the plants. With the availability of necessary nutrients in plants, the nutrients improves the quality of the plants. Healthy plants attracts insect pest, such as pea leaf weevils (Sitona lineatus), a major pest that damages the plant root and foliage, reduces the nitrogen fixation, nitrogen and yield of field pea (Pisum sativum). My research focused on how the Rhizobia-field pea symbiosis modulates the nutritional and defensive compounds of field peas, and how the symbiosis affects the behaviour and fitness of pea leaf weevils.