In the article parameters of photosynthetic apparatus and dependence of the efficiency and rate of photosynthesis on irradiance in flowering plant – parasitic dodder Cuscuta campestris colonized by gallinducing insect from the family of weevils Smicronyx smreczynskii were determined for the first time. Gall formation by Smicronyx smreczynskii is supposed to lead to the increase in the photosynthesis efficiency by the increase in the number of reaction centers of photosystem II of the dodder Cuscuta campestris