The results of intra- and inter-strain crosses carried out between the Ukrainian strains and the standard one are presented. Also inter-strain cross was made between strains from distant regions of Europe, i.e. from Spain and Ukraine. The results showed that strains coming from different localities in Ukraine as well as from the distant regions of Europe, i.e. Spain and Ukraine, or even originating from Europe and the USA, were not genetically differentiated within P. triaurelia. The studied strains can interbreed in spite of their geographical isolation. The results indicate that in the studied species of the P. aurelia complex there exists a type of breeding system which can be called moderate inbreeding.