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The European wheat stem sawfly, Cephus pygmeus (Linnaeus, 1767) and the black grain stem sawfly, Trachelus tabidus (Fabricius, 1775) are important and common pests in wheat growing areas of Turkey. These sawfly species continue to be a threat to wheat production in the southeast Anatolia Region of the country. This study was conducted to determine larval infestation rates and yield losses caused by these sawfly species in common wheat cultivars grown in the southeast Anatolia Region. Durum and bread wheat fields were surveyed to record larval infestation and damage caused by these sawfly species in four provinces (Adıyaman, Diyarbakır, Mardin and Şanlıurfa) of the region. A total 100 wheat fields were randomly selected and stem samples were taken from each field during the harvest period. Spike length, mean number of grains, grain weight and 1000-grain weight were recorded from 100 infested and healthy spikes and crop losses were calculated for 16 wheat cultivars. The surveyed provinces significantly differed in infestation rates, with the highest infestation level recorded for Diyarbakır province with a mean of 17.4% (range 2.1- 54.3%), while the minimum infestation was determined in Adıyaman province with a mean of 5.3% (range 1.4-17.3%). Durum and bread wheat cultivars had negligible effects on larval infestation. Spike length of infested wheat plants was reduced by 0.9-14.4% and the mean number of grains and grain weight were reduced by 0.5-19.7% and 7.2-28.5%, respectively. The loss in 1000-grain weight was 8.9% in bread wheat cultivars, while the loss was 7.9% in durum wheat cultivars. It was concluded that the loss in 1000-grain weight reached 10.9%. Therefore, appropriate control measures should be taken against stem sawflies in high-infestation locations. [ABSTRACT FROM AUTHOR]