Long-legged flies from CO₂-baited traps: new faunistic records and insights from bycatch analysis in Slovakia

Abstract

Although CO₂-baited BG-Sentinel traps are widely used for mosquito surveillance, their non-target bycatch can yield valuable faunistic information. We present the first assessment of Dolichopodidae (Diptera) collected inci-dentally using CO₂ traps across Slovakia in 2025. Of 290 weekly trap samples obtained at 16 localities, 45 (16%) contained dolichopodid specimens, representing a total of 400 specimens belonging to 13 species in five genera. Two species (Sybistroma impar (Rondani, 1843) and Systenus bipartitus (Loew, 1850)) are reported here for the first time in Slovakia. The most frequently recorded species were Systenus leucurus Loew, 1859, Medetera truncorum Meigen, 1824, and Sciapus platypterus (Fabricius, 1805), although their occurrence varied considerably among sites. The assemblage was dominated by species associated with arboreal and humid microhabitats, suggesting that CO₂-baited traps selectively capture only a subset of the local dolichopodid fauna. In addition, only male specimens were identified to species level, and therefore the reported species composition should be interpreted with caution. Our findings demonstrate that mosquito surveillance networks can provide valuable complementary faunistic infor-mation on non-target Diptera, including rarely recorded species. However, CO₂-baited traps do not yield a represen-tative sample of the dolichopodid fauna and should be considered as supplementary to targeted sampling methods. Integrating the analysis of bycatch into vector surveillance programs represents a low-effort approach to enhancing faunistic knowledge on Diptera in human-modified environments.

Key words: biodiversity monitoring, bycatch, CO₂ trap, Diptera, Dolichopodidae, new records, Slovakia