Estimation of the Recent Expansion Rate of Ruspolia nitidula (Orthoptera) on a Regional and Landscape Scale

SIMPLE SUMMARY: Recent changes in insect distribution are consistent with the effects of climate and habitat change. The bushcricket Ruspolia nitidula has expanded in Western and Central Europe in recent decades. In the Czech Republic, R. nitidula was recorded in 2006 after ca. 50 years of absence. Using available occurrence data from professionals and citizens we estimated the R. nitidula expansion rate from 2006 to 2020 in the Czech Republic. For comparison, we monitored in detail expansion at the areal margin in the Odra River basin from 2016 to 2020. To estimate the expansion rates, we used three different methods of spatial analysis, including least-cost path analysis with habitat suitability. The estimated maximum expansion rate ranged from 13.8 to 16.2 km/year based on occurrence data at the country level and from 11.1 to 11.7 km/year based on the monitoring in the Odra River basin. ABSTRACT: Recent changes in insect distribution are consistent with the expected interacting effects of climate and habitat change. The orthopteran Ruspolia nitidula has expanded its area of distribution in Western and Central Europe in recent decades. Because males emit a sound that is easily detected at a distance of up to 40 m, it is possible to detect spreading individuals and to therefore document routes and rates of spread. Using occurrence data at the landscape scale and three methods, including least-cost path analysis with habitat suitability, we estimated the R. nitidula expansion rate from 2006 to 2020 in the Czech Republic; this involved estimating distances between two origin occurrences in 2006 and two occurrences on the area margin in 2020. For comparison, we directly monitored expansion based on detection of singing males at the regional scale at the areal margin in the Odra River basin (2016–2020). The estimated maximum expansion rate ranged from 13.8 to 16.2 km/year based on occurrence data at the landscape scale and from 11.1 to 11.7 km/year based on the monitoring of males in the Odra River basin. To our knowledge, this is the first report of the direct monitoring of individual spreading males to detect changes in the distribution of an orthopteran.