The article is devoted to research on the effect of phytoncide properties of oak grown in plantations of forest and park area of Voronezh on the growth and development of oak gallflies. The aim is to study the oak pests - oak gallflies - small flying insects. The female of gall wasps makes injection on an oak leaf using the ovipositor and lays eggs in the wound, which is beginning to develop, and the next underlying cells and tissues begin to form sheet "nut" or plant gall. Soon the larva hatches from the egg and begins to work its jaws. All larval development occurs in the gall. It turns out that from the time of laying the egg and then the larva during all the time of its development are in close proximity to the plant tissues and phytoncides. So, oak leaf tissue is not toxic to the larvae of gallflies. Meanwhile, it is well known that volatile phytoncides of oak leaves are poisonous to many microorganisms including the very resistant, for example, for the dysentery bacillus. When laying eggs in the leaf tissue insects necessarily hurt it. Namely wound leaf increases the "production" of phytoncides, but it remains without consequences for the insect to adapt to phytoncides of oak leaves. This adaptation of some insects to poisonous phytoncides affects equally scientists. One of the major reasons of sanitary and hygienic influence of the forest is the antimicrobial effect of the volatile, which secrete plant organizations as they play an important role in chemical interaction of plants in phytocenoses, that was proved by the works of N. G. Kholodny, A. L.Kholodny, A. L. Chesovennaya (1987) – the number of phytoncides and their activity in one and the same species varies with conditions of oak forest location