The field work was performed at the experimental field of the Institute of Forage Crops, Pleven, Bulgaria during the period of 2006-2009. The share distribution of the orders Coleoptera, Thysanoptera, Diptera, Orthoptera and Hemiptera, suborder Sternorrhyncha, Heteroptera, Fulgoromorpha and Cicadomorpha was established for every four alfalfa growth cycles during the vegetation period for four years. It was found that the share participation of orders was determined primarily by the population dynamics of the dominant insect species and it was closely dependent on plant development following a characteristic course over the years. Depending on the food specialization and the division of the species into harmful and beneficial, the share of predators in regrowth corresponded to that of their prey. A clear trend was observed of increasing the share of harmful species and reducing the beneficial ones (Coleoptera, Thysanoptera, Hemiptera: Heteroptera) with the alfalfa development over the years.
Keywords: alfalfa, entomofauna formation, regularities