Studies for determination of species composition and seasonal dynamics of Coleoptera species in alfalfa biocenosis for forage were conducted in the 2007-2009 period in 2nd experimental field of IFC – Pleven. Important and permanent insect pests causing damage were Phytonomus variabilis, species of Sitona genius and Apion seniculus, which belong to fam. Curculionidae. Apion seniculus were reported for the first time in our country as harmful species in alfalfa. The attack by Apion seniculus was found when harvesting the first cut. The percentage of plants damaged by Apion seniculus varied from 8.7 to 23.3% on average.