Steinernema arenarium isolate CH was prepared at 22 °Ñ and used as a control in laboratory experiments on rearing in Galleria mellonella larvae at different temperatures (18 and 28 °Ñ). Host dead bodies were examined every two days. All reared adult nematodes were fixed in alcohol and mounted on permanent slides with glycerin solution in distilled water. The basic morphometric parameters (L, W, ES, ABD (CBD), T, V) were measured, and statistical analysis was performed. Morphometric data in males and females of both generations were shown to signifi cantly change depending on speed of growth and nutrients concentration. In both experimental groups, pygmy forms of adults were found.