Neonicotinoids have been used since the 1990s to protect against pests and are now the most widely used insecticides in the world. This group of insecticides includes seven active ingredients: imidacloprid, thiamethoxam, clothianidin, thiacloprid, acetamiprid, nitenpyram and dinotefuran. They are applied foliar over the leaves, by seed treatment and application in the form of granules. About 60% of the neonicotinoids produced are used specifically for seed treatment and in the form of granules. Although the insecticides in this group have low acute toxicity to mammals, birds, and fish, negative phenomena are associated with the use of neonicotinoids on bees. Bees exposed to sublethal doses of this insecticide may develop various problems (e.g., flight and orientation problems, loss of sense of taste and foraging ability), and their ability to overwinter is reduced. The active ingredients imidacloprid, clothianidin, dinotefuran and thiamethoxam are very toxic to bees, while the active ingredients thiacloprid and acetamiprid are moderately toxic to bees. The problem of the decline or loss of bee colonies is present worldwide. For example, between 1981 and 2005, the number of bee colonies in the United States declined from 4.2 to 2.4 million, and in southern Europe there was a loss of about 40% of bee colonies. Colony Collapse Disorder (CCD) is also associated with the use of insecticides from the group of neonicotinoids, such as the negative effects of harmful organisms on bees Varroa destructor Oudemans, the appearance of fungal diseases and viruses, the reduction of pasture area and problems with the queen. In 2013, the European Commission temporarily banned the use of three insecticidal active ingredients from the neonicotinoid group (imidacloprid, thiamethoxam and clothianidin) for two years due to suspicions that insecticides from this group have harmful effects on bees. The ban covered the treatment of seeds and soils for crops that attract bees and spring cereals, while the authorization remained valid for the treatment of winter cereals and sugar beet seeds and for use in protected areas, as well as for foliar treatment after flowering. The final ban was issued by the European Commission on April 27, 2018, on the recommendation of the European Food Safety Agency (EFSA) based on a thorough review of all relevant research. The decision refers to a complete ban on the use of imidacloprid, thiamethoxam and clothianidin, except in permanent greenhouses, and the plants obtained in this way remain in a permanent greenhouse throughout their lifetime. The ban on the use of three insecticidal active ingredients from the neonicotinoid group has raised concerns about the potential impact on agricultural production. Surveys conducted immediately after the temporary ban showed that in some crops, such as oilseed rape, pest infestations increased significantly, more insecticides (mainly from the pyrethroid group) were applied foliar, and yields decreased significantly (by up to 15%). The main aim of this doctoral thesis was to determine the impact of the ban on the use of active substances from the group of neonicotinoids, widely used as insecticides in seed treatment, on the occurrence of pests in agricultural production and on the condition of bee colonies in eastern Slavonia, a part of Croatia with intensive arable production. Because there are few insecticidal active ingredients that can be used for seed treatment of field crops, it was necessary to investigate the efficacy of alternative, more ecotoxicologically favourable insecticides that could be considered as substitutes for the banned neonicotinoids. Precisely for this reason, the research conducted in this dissertation is based on the main hypothesis that the ban of neonicotinoids in Croatia does not have a positive impact on bee colonies in areas where arable production is predominant, because the losses of bee colonies in these areas are within normal and acceptable limits from the point of view of bee production (up to 10% per year). The second hypothesis was that the alternative insecticides spinosad, chlorantraniliprole and azadirachtin, used in seed treatment of corn and sugar beet, are acceptable substitutes for neonicotinoids due to their good effect on pests. To prove the established hypotheses, the following objectives were set for this study: (a) Analysis of data on crop area, pest incidence and damage, crop protection measures, insecticide treatment index, and type of insecticides used before and after the ban on neonicotinoids; (b) Analysis of data on the number of bee colonies, type of bee pasture and supplemental feeding, treatment of bee colonies for diseases and pests, number of bee colonies in the fall and number of bee colonies after wintering in the spring during the period studied, and losses and causes of losses of bee colonies during wintering and vegetation, (c) Determination of the type and level of insecticide residues in dead bees in pest infestations associated with insecticide use, (d) Determination of the efficacy of spinosad, chlorantraniliprole, and azadirachtin in seed treatments against important pests of arable crops: corn and sugar beet. In Croatia, arable crops and gardens account for more than half of the total arable land, and the main agricultural crops considered in this study are wheat, barley, corn, sugar beets, oilseed rape, sunflower, and soybeans. Since pests have the highest damage potential (18%) next to weeds, the dissertation also deals with the most important pests of arable crops, paying special attention to the wireworms, the sugar beet weevils and the sugar beet flea beetles as pests that were used in laboratory trials during the research. In addition to agricultural production, beekeeping is also of great importance. In addition to the direct benefits that bees bring through the production of honey and other bee products, they also create indirect benefits through the pollination of plants (they pollinate about 80% of flowering plants and, together with other pollinators, more than 70% of the plants that feed humans). In addition to the negative effects of pesticides, bees are susceptible to various diseases and pests, and poor beekeeping practices, queen problems, and a lack of highquality forage and less pasture (nectar and pollen) can also negatively impact bees. Losses of bee colonies can occur in winter or during the season, i.e. during grazing. In 2008/2009, winter losses in Croatia amounted to 13.16%, in 2012/2013 to 9.5% and in 2015/2016 to 16.4%. After the ban on neonicotinoids, the number of insecticides for seed treatment and foliar application declined, so that today there are no approved insecticides for treating sunflower seed to protect against wireworm, for treating corn seed to protect against western corn rootworm, and for treating sunflower and sugar beet seed to control aphids. Alternative insecticides, i.e., candidates that could replace the banned neonicotinoids, are chlorantraniliprole, spinosad, and azadirachtin. Chlorantraniliprole is a systemic insecticide with low bioconcentration potential and low toxicity that is selective for beneficial arthropods, making it suitable for use in integrated pest management. Spinosad is a fermentation product from the soil bacterium Saccharopolyspora spinosa Mertz and Yao. It belongs to the group of biological insecticides, naturalites, and is less toxic to beneficial insects than other insecticides. It has low toxicity to mammals and the environment. Azadirachtin is a biological insecticide obtained as a product from the neem plant (Azadirachta indica Juss). It has a negative effect on the feeding, development, and reproduction of pests, and when used properly, it is not expected to have harmful effects on humans, wildlife and the environment, as well as on other beneficial insects. The dissertation included surveys of farmers and beekeepers, as well as laboratory testing of the efficacy of alternative insecticides and analysis of data on the causes of bee mortality obtained from an approved laboratory for residue determination. In Tovarnik, a town in eastern Croatia, a survey of farmers and beekeepers was conducted from 2014 to 2016. Since bee losses occurred in Tovarnik during the 2015 growing season, data on the causes of the losses were analysed, which came from the approved laboratory for residue determination, the Croatian Veterinary Institute in Zagreb. Laboratory investigations were carried out in 2016 and 2017 to assess the effectiveness of spinosad, chlorantraniliprole, and azadirachtin as treatments for corn seeds against wireworms. Additionally, in 2017, the same compounds were examined for their efficacy in treating sugar beet seeds against the sugar beet weevil and sugar beet flea beetle. The results of the surveys were processed using standard statistical methods to determine mean and variability (ANOVA) (ARM 9, Gylling Data Management), and the efficacy of the alternative insecticides was calculated on the basis of wireworm mortality according to Abbott (1925). The efficacy data were processed using statistical factor analysis (ANOVA) and ranked using the Duncan rank test (ARM 9, Gylling Data Management). Since the mortality of sugar beet weevil and sugar beet flea beetle in the experiments was read in 24-hour time intervals, the data on the number of living individuals exposed to the effects of the insecticides used were processed with the Kaplan-Mayer method of survival analysis in the R programming environment using special packages for descriptive and inferential statistical analysis (packages "survival", "ggsurvfit" and "survminer").The results of the surveys among farmers show that agricultural production dominates in the Tovarnik region (on 97.32% of the total agricultural area), and the questionnaire covered most of this area (71.87% in 2012/2013, 72.38% in 2013/2014 and 90.36% in 2014/2015). In all survey years, only sugar beet seed was treated with insecticides from the neonicotinoid group on all croplands (the temporary ban did not apply to this crop), while sunflower seed was treated with the same insecticides in the 2012/2013 cropping season (on 73.99% of the croplands of this crop), before the ban on the use of insecticides from this group came into effect. Of the other active substances, during the ban on the use of neonicotinoids, corn seeds was treated with an insecticide from the pyrethroid group (e.g. tefluthrin) and sugar beet seed was treated with a combination of neonicotinoids (the ban on use did not apply to this crop) and pyrethroids.Appropriate pneumatic seeder were used for sowing neonicotinoid-treated seed in both crops (an exception was sugar beet seed in a 4-ha plot in 2014, where a mechanical seeder was used). In certain growing seasons, pests of small grains (cereal leaf beetle), sugar beets (sugar beet weevil), soybeans (painted lady) and oilseed rape (cabbage stem weevil, common pollen beetle) were controlled on a leaf-by-leaf basis, with preparations containing active ingredients from the neonicotinoid group not being used. Due to the occurrence of high pest populations, insecticide treatment indices increased in the 2012/2013 and 2014/2015 growing season in sugar beets (2,9), small cereals (0,97) in 2012/2013 and (0,99) in 2014/2015, and canola (2) in 2014/2015. Expert estimates of the treatment index for these crops are 2.5; 0.2; 1. Yield data for sunflower sown from neonicotinoid-treated seed only showed significantly higher yields (4.20 t/ha) compared to sunflower sown from untreated seed (2.56 t/ha). The survey of beekeepers included most colonies in Tovarnik (83.52% in 2013, 90.32% in 2014 and 86.67% in 2015). The bees collected nectar and pollen according to the pasture plan in the area, and the beekeepers fed with sugar syrup and sugar cakes. Winter losses of bee colonies were in accordance with expected and acceptable losses of bee colonies (6.02% in 2013/2014, 8.79% in 2014/2015 and 11.54% in 2015/2016). In the 2013 season, the loss of three bee colonies was reported, and in 2015, the death of 33 % bee colonies was reported. The results of the approved laboratory show that the cause of the loss of bee colonies during grazing in 2015 was the treatment of sunflowers with the product in a combination of the active ingredients chlorpyrifos from the group of organophosphorus insecticides and cypermethrin from the group of pyrethroids, although this product (Chromorel-D) had no approval for use on sunflowers. Laboratory studies show that chlorantraniliprole (efficacy less than 15%) and azadirachtin showed no efficacy against wireworms in the treatment of corn seed, while spinosad is very effective at dosages of 3.5 and 5 mg/kg seed (efficacy about 70%). Chlorantraniliprole, spinosad, and azadirachtin showed low efficacy against sugar beet weevil (in terms of pest mortality). Chlorantraniliprole showed good efficacy against the sugar beet flea beetle in treating sugar beet seed (pest mortality at a dose of 0.2 mg and at a dose of 0.6 mg). Spinosad also showed excellent results against this pest at all doses. In addition, azadirachtin also showed excellent efficacy against sugar beet flea beetle at all doses. Factorial analysis of laboratory test results has shown that insecticide efficacy depends on the type of insecticide, dose, and duration of insecticide exposure.