The present study aimed to determine the rate of microsporidiosis in larvae and adult beetles in Calosoma sycophanta L. (Coleoptera: Carabidae) mass-rearing laboratories. Eighty larvae and 7420 adults of C. sycophanta were dissected from the mass-rearing laboratories and investigated for the presence of microsporidiosis. Microsporidiosis was determined in all localities. Four hundred and forty-one adults of the dissected insects were found to be infected and the total infection rate was 5.94%. A total of 80 C. sycophanta larvae from Balikesir and Isparta examined in 2016 showed no microsporidiosis. The infection ratio was varied among populations and years. The total infection rate per year was 2% in 2015, 3.85% in 2016, 5.7% in 2017, and 12.3% in 2018. It was observed that microsporidiosis increases year after year. In addition, infection rates reached considerable levels, such as 26.3% in Izmir, 31.1% in Antalya, 30.2% in Balikesir, and 35.2% in Mersin localities. During the study, microsporidiosis in male and female beetles was also investigated. Twenty-four (2.49%) of 963 male and 41 (2.99%) of 1370 female beetles were found to be infected. 'These results confirm that the microsporidian pathogen has a high dispersal potential through the C. sycophanta mass-rearing laboratories and can be an undesirable suppressing factor in adult beetles.