Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 13 2 2018 06 25 244 250 Mustafa YAMAN Dept. of Biology, Faculty of Science, Karadeniz Technical University, 61080, Trabzon, Turkey AND Faculty of Arts and Science, Abant İzzet Baysal University, 14030, Bolu, Turkey 2018 06 25 2018 06 25 Background: Chrysomela (=Melasoma) populi is one of the most serious pests on poplar plantations. In the present study, a microsporidian pathogen, Nosema melasomae infecting Crysomela populi is re-recorded from a new geographical locality and its spore ultrastructure is given for the first time. Methods: Larvae and adults of C. populi were dissected in Ringer’s solution and prepared wet smears were examined under a microscope. Detected fresh and stained spores were measured and photographed using an Olympus BX51 microscope with a DP-25 digital camera and a DP2-BSW Soft Imaging System. The ultrastructure of the pathogen was studied with a Philips EM 208 transmission electron microscope using standard preparation techniques as previously described Results: Fresh spores of the microsporidian pathogen are elongate, 4.86 ± 0.71 µm in length and 1.64 ± 0.19 µm in width. The spore wall is considerable thin, measured 60 to 100 nm and consists of a clear endospore (40 to 80 nm) and an electron-dense, uniform exospore (15 to 30 nm). The polar filament is isofilar and has only 6-8 coils. Nuclei in the cell are 400-560 nm in diameter. The polaroplast has a thin lamellated structure. Conclusion: The pathogen from C. populi is N. melasomae Sidor & Jodal, 1986 and its systematic position given by Sidor and Jodal. The spore ultrastructure of N. melasomae differs from those of other microsporidia infecting chrysomelids. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/2207 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/2207/832