Stereonychus fraxini – ash weevil, is an insect pest species widespread in the southern and central Europe, northern Africa and Asia Minor, taxonomical affiliated to Insecta class, Pterygota subclass, Coleoptera order, Curculionidae family. Ash weevil is an important insect pest that defoliate the tree and shrubs species from the olive family Oleaceae: Olea sp., Fraxinus spp., Phillyrea latifolia, Syringa vulgaris. The S. fraxini is a serious defoliating forest pest that cause damage in both active stages (larva and adult). During the last years, its populations (breeding coefficient) have increased and produced mass defoliation of Fraxinus spp. trees, which caused important economic damages. In the Republic of Moldova ash weevil hibernate as adults in soil, bark cracks and under the moss on the trunk. Per year, ash weevil develops two generations that usually overlap one another (overlapping period being from 15 to 30 days). The first generation of S. fraxini develops during the last 10-day period of April until June (in mature ash wood it emerges approximately one week later). Staggered adult emergence coincides with the beginning of ash bud swelling. The second generation is hibernating and usually lasts from May until April of the next year. The weevil adults are actively in sunny days, when they can be observed on the top of terminal buds, sucking sap bud or perforating tree leaves (avoiding the thick nervures). When the weather becomes cold and rainy, the adults hide under various shelters. In the first life days, the adults need a supplementary feeding for to maturation the sexual organs. Depending on abiotic factors, the breeding period is very long (until 30 days). The female’s prolificacy is maximum 17 eggs and oviposition is staggered, the eggs being laid by one or grouped by 2-5 less 11. These female laid the eggs under the scales buds and / or in the leaves main veins. Embryonic development takes just a few days, the larval period last 10 - 14 days and the pupal up to a week. The attack mode of this pest is diverse: from penetration and consummation of leaf primordia in overwintering buds by larvae; sucking sap of terminal buds – by adults; until consumption of the leave’s bottom mesophyll, leaving untouched the upper epidermis by larvae and adults. During of vegetation period of 2015 were fixed outbreaks of S. fraxini in all ashwooded zones of the country, indifferent with pure or mixed composition (where common ash is a predominant wood species). According to detailed forest-pathological research materials in 2015 the surface of outbreaks of this pest covered 3685 ha, which is by 2,2 times or with 44,53 % less than in previous year which was 8276 hectares. In 2015, the outbreaks of ash weevil has occupied an area of 811 hectares, while on a surface of 1070 hectares the outbreaks have expanded. Furthermore, on 4332 hectares the outbreaks were liquidated by using combating measures. Because in 2014 records of cocoons of S. fraxini were done only in two sample plots from five, we took for analysis the data from 2013. In the result of achievement of analysis of stationary surveillance materials (the below table), is resulting that in 2015 density of ash weevil’s cocoons are in the limit from zero to 14.1 cocoons on 0,125 m2. Compared to data from 2013 and 2014 years this index decreased in all SPA (the sample permanent areas). Breeding coefficient in 2015 was equal to 0 or less than 1, showing a diminution of population of this pest. If to compare the viability percentage of adults in SPA with previous years, it can firmly conclude that the index is decrease significantly, excluding SPA from Codrii Natural Reserve where the index is almost the same as in 2014. In the same time, in 2015 the index of the cocoons affected by entomophagous insects in all SPA was in increase, oscillated between 14,2 and 79,4 %, the highest index being fixed in SPA Hinceşti – 79,4 %. During the vegetation period of 2015 in SPA Nisporeni and Orhei were not fixed any cocoons of S. fraxini. Cocoons affected by predators (33,3 % out of 100 %) were just recording in the SPA Bender. Averages of defoliation caused by ash weevil in the reporting year was lower than in 2013 and 2014. The degree of defoliation reached 37 % in SPA Bender, 17 % in Hincesti SPA, in the other sample permanent areas defoliation values did not exceed 5-10 %. Proceeding from the analysis of weather conditions, forest-pathological detailed research materials, pest population indices and defoliation degree of ash forests caused by the S. fraxini in 2013 - 2015 allow us to make the following conclusions: IX-th International Conference of Zoologists, 12-13 October 2016 281 - In the SPA studied were collected from 0,7 to 6,7 ex. / 0,125 m2, which tell us that the degree of defoliation correlated between 3 and 23 %. The maximum density of viable adults was 8 ex / 0,125 m2, which correspond to 27 % defoliation caused by ash weevil. - Based on the forest-pathological detailed research materials carried out in 2015, only in SPA “Plaiul Fagului” was recorded a higher degree of defoliation caused by this pest (50-86 %). - The expected level of defoliation in 2016 caused by ash weevil is between 10-30 %, and in some areas even to 50-90 %.