Comparing Hymenoptera biomass using malaise traps in suburban and rural Maryland

Hymenoptera play vital roles in terrestrial ecosystems, including acting as pollinators, predators, and parasitoids. Potential widespread insect declines threaten Hymenoptera biodiversity, abundance, and biomass and the services they provide. We participated in a continent-wide survey investigating insect declines, the North American Insect Abundance Network (NAIAN), which uses Malaise traps for insect biomass assessment. We measured total insect biomass and biomass of Hymenoptera at two locations in central Maryland: on the McDaniel College campus in the city of Westminster, and at the McDaniel Environmental Center (MEC), a rural, semi-natural field station located 8.5 km from the main campus. We attached jars of 70% ethanol to the Malaise traps for three-day periods that coincided with key life stages of insectivorous tree swallows (Tachycineta bicolor), following NAIAN protocols; we increased temporal coverage with three additional sampling periods in the early growing season. We hypothesized that total insect biomass and the biomass of Hymenoptera would be greater at the rural MEC location, which has more natural areas and fewer chemical inputs. In samples corresponding with swallow egg laying, we found 2.3 times greater total insect biomass and 6.4 times greater Hymenoptera biomass at the MEC compared to campus, with Hymenoptera also comprising a greater proportion of insect biomass (12.3% vs 4.5%). Our early-season findings support our hypothesis that more natural areas support greater insect biomass and highlight the need to account for landscape context when working to understand long-term insect biomass trends.