caliroa cerasi, or "pear slug", causes important damages in cherry orchards of the lower valley of the chubut river. the principal aim of this work was to know their biology and poputation dynamic in this region, being these aspects basic to develop management strategies compatible with a pest integrated management programme. for this purpose, a scouting in three commercial orchards and in an experimental inta chubut plot during two consecutives growing seasons (2005/2006 y 2006/2007) was held. these consisted in the adults capture by chromatographic traps meanwhile in case of eggs and larvae, a direct sampling was done. in order to ajust sampling technics, during the second growing season, two stratum of the plant (lower and medium) were considered. population density was high in an organic production. population fluctuations indicate that the species present three generations annually in virch. significant differences in eggs levels between plant stratums were found only in two dates in an orchard conducted by a "central axis" system, but no in larvae case.