Elm leaf-beetle is a major pest of ulmus trees (Ulmus densa L. and Ulmus glabra L.) which causes considerable damage every year. In an investigation in the year 1998 in Qazvin, the bioeclogy of this pest was studied. For this purpose, in each species of elm, 20 trees from 10 different areas were randomly selected. During weekly sampling, from each tree 40 samples (10 samples from every 4 cardinal directions) in lower one third part of crown were randomly selected. In each sampling, number of egg mass and larval instars in each sample unit (i. e. leaf) and for each geographical direction were separately recorded. The degree days of different life stages were calculated based on maximum and minimum daily temperatures. In order to determine the damages caused by different generations, 40 samples from the entire crown were randomly selected and the damage level due to each sample was compared with 10 control samples that were damaged between 0-100 percent at the end of each generation. The results indicated that, this insect had 4 periods of activity and probably 4 complete generations in Qazvin climatic conditions that overlap each other. First and last generations had the maximum and minimum duration as well as population density, respectively. Population density for different life stages of this insect in main cardinal directions did not show any significant differences at 1% level. Based on calculated degree days the best controlling time were proposed at 245 and 407 DD for first and third larval instars, respectively. The damage caused by second and third generation insects onwards were considerable for U.glabra and U. densa، respectively.
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