Loss of parasitoid diversity in China’s corn agro-ecosystem over a 30-year time period

Globally, insect abundance and diversity are experiencing a rapid decline. Despite important inter-taxa and geographical variability, this can entail an extinction of ecological interactions and a decay of ecosystem functions. In this study, we compared the spatial distribution, abundance and species composition of Trichogramma spp. egg parasitoids (Hymenoptera: Trichogrammatidae) over a 30-year time period in China. During the 1980s and in 2016–2018, egg masses of the Asian corn borer (ACB), Ostrinia furnacalis , were systematically sampled from corn fields across the country. In 2018, five species were identified with Trichogramma ostriniae representing 90% of the species complex. Since the 1980s, two new species have made their appearance while nine (out of 12; i.e., 75%) species disappeared. These include comparative specialists but also generalists such as T. evanescens and T. exiguum . Across sites, species richness (R) and diversity (Shannon-Weiner index) have declined by a respective 25–86% and 56–100% (except for Heilongjiang province) over this time frame. We hypothesize that this is attributed to land use change, pesticide use and plant diversity decline in agro-landscapes. Conversely, no negative impacts were detected of augmentative biological control. Given the drastic reduction in ACB parasitoid richness, agro-ecological measures and diversification strategies should be deployed to restore the ecological resilience of local farming systems. Our work carries major implications for food security and helps to muster support for more nature-friendly, pest-resilient farming systems in China and abroad.