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The aim of this research was to study the influence of two insecticides on spore germination and gametophyte differentiation in Asplenium scolopendrium and Athyrium filix-femina, non-target species of leptosporangiate pteridophytes. The insecticides used are from the neonicotinoids class and they contain thiametoxam 25% (T) and acetamiprid 20% (A). The experimental variants were T1-0.005%T, T2-0.01%T, T3-0.02%T, A1-0.005%A, A2-0.01%A, A3-0.02%A and the Control variant (C)-Knop solution. The spores were cultivated in 50 ml of experimental solutions. The culture vessels were kept in the growth room at controlled temperature, humidity and luminosity levels. The percentage of spore germination was determined after a week. Furthermore, microscopic observations were performed on gametophyte development after 3, 6 and 14 weeks, respectively from the initiation of cultures. Spore germination was influenced by both insecticides. In the case of thiametoxam, germination percentages decreased from 90% for the control variant to 81% in Athyrium filix-femina and 66% in Asplenium scolopendrium for the T3 variant. The acetamiprid reduces the germination percentages to 0% for the A3 variant in both species tested. The use of acetamiprid leads to delays in gametophyte differentiation. Of the two non-target species tested, Asplenium scolopendrium exhibited a more pronounced sensitivity to the effects of insecticides. [ABSTRACT FROM AUTHOR]