Nature conservation and insect decline in Central Europe: Loss of Lepidoptera in key protected sites is accompanied by substantial land cover changes

The insect biodiversity crisis affects diverse cultural landscapes as well as natural and semi-natural habitats. Accordingly, the effectiveness of protected areas in conserving insect communities needs to be evaluated. We employed photo-interpretation of aerial photographs from the past (1938-1947) and present (2014-2019) to analyse changes in natural habitats with diverse canopy cover in seven long-term protected areas (jointly called 'reserves') in the Czech Republic, Central Europe, and evaluated potential links between these changes and butterfly and moth (Lepidoptera) declines. We observed a marked decrease in habitat heterogeneity, largely due to the expansion of closed-canopy forests at the expense of semi-open habitats (e.g. forest steppes, open woodlands) and open grasslands. An analysis of faunistic records of 162 species of butterflies and 160 species of macro-moths before and after 2000 showed that, on average, the reserves have experienced losses of 26% of butterfly species and 19% of moth species. Trait-based analyses suggested that the losses were associated with particular life-history traits. Non-generalist butterflies with a short period of seasonal flight activity, and moths associated with grasslands and with non-feeding adults, had a greater probability of going missing (meaning potentially locally extinct) in the reserves. These findings suggest that conservation efforts should prioritise active management that aims to restore habitat heterogeneity in order to mitigate the ongoing trend of insect decline.