Insects present one of the most important harmful factors for forest ecosystems. Very often ash weevil outbreaks in Serbia indicate necessity of establishment of system for its control and short term damage prognosis. Damage intensity can be evaluated by comparison of needed amount of food for present number of insects with available amount of food. This paper investigates possibility for short-term prognosis of ash weevil damages on the basis of larval abundance on leaves from the end of April till mid-May. Dividing the average leaf area and leaf area eaten by one larvae and successional adult insect shows that average of 11.8 larvae per leaf results in total crown defoliation. Defoliation of 25% which impacts tree growth can be achieved by 3 larvae per leaf.