Comparative analysis of cytogenetic effects of the neonicotinoid insecticides Nuprid 200 SL and Calypso 480 SC on Allium cepaL cells. Ivan Y. Stoyanov *, Penka L. Vasileva, Teodora A. Staykova, Magdalena L. Simidareva, Petya I. Rusinova, Iliyana I. Ilieva, Evgeniya N. Ivanova University of Plovdiv ”Paisii Hilendarski”, Faculty of Biology, Department of Developmental Biology, Section of Genetics, 24 Tsar Asen Str., Plovdiv 4000. Corresponding author: ivan100yanov@abv.bg Introduction Material and methods Results Table 1. Mitotic indices (in %) in Allium cepa, treated with different concentrations of Nuprid 200 SL and Calypso 480 SC. Samples Mitotic index Samples Mitotic index Control 51.58 ±1.50 Control 51.58 ±1.50 Nuprid 25 25 mg.l-1 imidacloprid 47.32 ±7.82 Calypso 25 24 mg.l-1 thiacloprid 49.85 ±6.56 Nuprid 50 50 mg.l-1 imidacloprid 45.71 ±4.05*** Calypso 50 48 mg.l-1 thiacloprid 49.04 ±10.79 Nuprid 75 75 mg.l-1 imidacloprid 46.54 ±1.83*** Calypso 75 72 mg.l-1 thiacloprid 48.16 ±4.39 Nuprid BS 100 mg.l-1 imidacloprid 46.55 ±2.46*** Calypso BS 96 mg.l-1 thiacloprid 46.60 ±4.35* Samples Total frequency of chromosomal aberrations CAI (%) Frequency of chromosomal aberrations among dividing cells (%) Control 0.27 ±0.24 0.53 ±0.29 Nuprid 25 25 mg.l-1 imidacloprid 0.45 ±0.15 0.97 ±0.27* Nuprid 50 50 mg.l-1 imidacloprid 0.48 ±0.20 1.05 ±0.41* Nuprid 75 75 mg.l-1 imidacloprid 0.65 ±0.27* 1.41 ±0.60** Nuprid BS 100 mg.l-1 imidacloprid 0.70 ±0.41*** 1.49 ±0.84*** Calypso 25 24 mg.l-1 thiacloprid 0.48 ±0.29 0.92 ±0.49 Calypso 50 48 mg.l-1 thiacloprid 0.54 ±0.19* 1.17 ±0.47* Calypso 75 72 mg.l-1 thiacloprid 0.55 ±0.21* 1.12 ±0.41* Calypso BS 96 mg.l-1 thiacloprid 1.07 ±0.38*** 2.29 ±0.77*** p < 0.05*; p < 0.01**; p < 0.001*** p < 0.05*; p < 0.01**; p < 0.001*** Neonicotinoids are a major class of insecticides developed over the last 30 years that are used to increase crop yields. Their use is associated with a number of adverse environmental effects. The potential genetic risk of neonicotinoids requires extensive study of their genotoxicity, using a variety of approaches and test systems. In this study, we evaluated the cytostatic and mutagenic effects of the neonicotinoid insecticides Nuprid 200 SL (with the active substance imidacloprid) and Calypso 480 SC (with the active substance thiacloprid) on the cells of the root meristem of Allium cepa L. Table 2. Frequency of chromosome aberrations analyzed by the Allium test For the purposes of our study, bulbs from Allium cepa, provided by the Maritsa Institute of Vegetable Crops - Plovdiv, were used. From the tested pesticides, stockworking solutions (BS) were prepared according to the instructions of the producers in a concentration that is recommended for use in agricultural practice. Working solutions with lower concentration - 75%, 50% and 25% of the experimental solutions for each pesticide were prepared from the stock solutions. The use of the Allium test system (according to Fiskesjö, 1985) allows for a combined approach in cytotoxicity and mutagenicity studies by applying genetic methods. The cytostatic action of pesticide solutions in different concentrations was determined by calculating the total mitotic index and phase indices. Genotoxicity was assessed by determining the frequency of chromosomal aberrations in Allium cepa meristem cells using an anaphase method and a micronucleus test. Data from the present study indicate that the insecticides Nuprid 200 SL and Calypso 480 SC have a cytostatic effect by inhibiting cell division from the root apical meristem of Allium cepa. The value of the mitotic index is lower than the control variant at all tested pesticide concentrations (Table 1). The comparative analysis of the mutagenic action of the studied pesticides shows a higher genotoxic potential of Calypso 480 SC. Stock solutions of both pesticides induced chromosomal abnormalities in Allium cepa cells with a much higher frequency than the control, but the chromosomal aberration i