Sampling requirements for standardized insect biodiversity monitoring vary with abundance

Global biodiversity loss is raising concerns for civilization, which relies on ecosystem services for life-sustaining processes. Monitoring is then critical to detect and remediate sources of environmental degradation. Insect species are indicators of ecological health and are vital for monitoring projects. However, methods for monitoring insect biodiversity vary in sampling effort, which creates difficulty in comparing outcomes across different studies, locations, seasons, taxa, and habitats. We analyzed DNA-metabarcoding Malaise trap data for three insect orders (Hymenoptera, Lepidoptera, Coleoptera) from 64 sites across an agro-ecosystem landscape in southern Ontario to determine how taxon, seasonal abundance, and habitat type affect the effort required to estimate insect species richness to achieve a given degree of precision. During seasonal periods of high insect abundance, reduced effort was needed to achieve 90% precision in estimating species richness, whereas the opposite was true during periods of low abundance. Although these trends were consistent across orders, the magnitude of effort required to estimate 90% of the species richness at a given location varied across habitat types. These results suggest that insect abundance is a key variable determining the degree of sampling effort needed to standardize biodiversity assessment.