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

Globally, insects are undergoing a rapid decline in abundance and diversity. Despite varying degrees of scientific attention across insect taxa and geographies, these patterns 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 in multiple key farming regions. In 2018, five species were identified using morphological and molecular methods, with Trichogramma ostriniae representing 90% of the species complex. Since the 1980s, two new species have made their appearance (i.e., T. brassicae , T. bilinggensis ), while nine (out of 12; i.e., 75%) species have disappeared. Across sites, species richness and diversity have declined by a respective 25–86% and 56–100% (except for Heilongjiang province) over this time frame. We hypothesize that this loss of functional diversity is attributed to the progressive intensification of corn cropping systems, involving landscape simplification, pesticide use and the loss of (crop, non-crop) plant diversity. Conversely, no evidence was found that augmentative biological control (as compared to pesticide-based measures) negatively affected the resident parasitoid community in farm settings. 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 thus carries major implications for food security and helps to muster support for more nature-friendly, pest-resilient farming systems in China and abroad.