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This is a misunderstanding because of problems with my English ...
I meant the low abundance of the species.

Pestov SV, Dolgin MM. Tabanid fly (Diptera, Tabanidae). - SPb .:, 2013. 190 pp. (Fauna of the European Northeast of Russia, Tabanid fly, T. XI, part 1) on page 37 about Chysops divaricatus the following is given. Quote:
Sporadically occurs only in the southern and middle taiga. Relative abundance is less than 1%.
On page 170 for the southern taiga is given with an abundance grade of 1 rank (low abundance of the species), for the middle taiga with a grade of 3 ranks (common species).
According to the finds, 1-2 individuals are found in different places of collection. For the North, Chrysops diviricatus is an insect with a low relative abundance.