The article is an evaluation of studies on toxical effects of fluor and magnezite immissions on insect development. In screening tests the doses of lethal toxicity (DL50) have been established and are described the changes in vital processes (mortality, prolongation of development, morphological deformities of pupae and imagos, changes in histological structure of ovaries, fertility) observed in continual insect–keeping of model insect species on a semisynthetical diet with an increased content of NaF and magnezite ash. As limit values of toxical influence on insects have been established the following contents: 4–4.5 mgF on 100 g of dry matter of nutriment and 1 % of Mg in dry matter of nutriment. On the basis of immission situation in Slovakia the importance of fluor and magnezite immissions is evaluated as a new ecological factor effecting the insect development.