Sugar beet is one of the most important crops in the world. Annually, 277 million tons of sugar beets are produced worldwide. During the period of vegetation, sugar beet is exposed to a large number of pests that must be controlled to ensure high yields. One of the most important pests is sugar beet flea beetle (Chaetocnema tibialis Illiger 1807). Sugar beet flea beetle is a pest in the early growth stage of sugar beet. Control of flea beetle was successfully carried out by sowing seeds treated with systemic insecticides from the group of neonicotinoids. As of 2018, the use of neonicotinoids is prohibited, therefore it is expected that flea beetle will have to be controlled with foliar insecticides for which there is a suspicion of resistance development. The appearance of resistance can have serious consequences for production. Therefore, knowledge of pest susceptibility status to insecticides is necessary in order to avoid or mitigate the negative consequences that the appearance of resistance may cause. The aim of this study was to determine the effectiveness of organophosphorus insecticides, pyrethroids and neonicotinoids on the mortality in adult developmental stage of flea beetle within six localities in the area of intensive sugar beet cultivation in Croatia. For the purposes of the experiment, empty glass vials were treated in which flea beetles was discharged after treatment and drying. The number of dead or dying insects was determined in the reading. The classification of results was carried out on the basis of determined mortality, and populations were classified as highly sensitive, sensitive, moderately resistant, resistant, and highly resistant. All tested populations of sugar beet flea beetle were highly sensitive to the use of chlorpyrifos. Three populations were resistant to the use of lambda-cyhalothrin, and three populations showed moderate resistance. All populations showed high resistance to thiacloprid. The achieved results indicate that sugar beet flea beetle has started to develop resistance to pyrethroids, and only pyrethroids are currently allowed in the Republic of Croatia for its foliar control. Therefore, it is necessary to find new ways to control sugar beet flea beetle, which include the introduction of new insecticides, but also new methods of control. Otherwise, damage from sugar beet flea beetle could become a limiting factor in sugar beet production.