To understand the plight of insects, entomologists look to the past

Abstract

Plumbing a variety of historical data could offer important insights into trends in insect declines. When avian ecologist Nicholas Rodenhouse moved offices a few years ago, he found a potential treasure trove of data buried in some old file cabinets. Piles of forgotten spreadsheets catalogued taxonomic records of beetles collected in the hardwood forests of Hubbard Brook, NH, between 1973 and 1977. The research was originally meant to speak to the diets of local birds. Convinced that the spreadsheets could serve anther purpose, Rodenhouse, now emeritus at Wellesley College in MA, decided to ask his undergraduate mentee, Jennifer Harris, to resample the old research sites. Her work, conducted between 2015 and 2017, would tease a new story from the old data, one that could inform ongoing mysteries about how and why some insects seem to be disappearing (1). Some insect populations are declining—even ostensibly versatile species such as Central California’s large marble butterfly, Euchloe ausonides. Researchers are tracking trends through long-term insect count data and using historical data. Image credit: Joyce Gross (University of California, Berkeley). Harris collected beetles the same way the seventies-era researchers had done, using window traps: clear pieces of glass above a small trough of water. Beetles flying low to the forest floor hit the glass and fell into the water, drowned, and were later retrieved. Between 2015 and 2017, the researchers checked window traps at three different elevations twice a week from mid-May through early August and identified beetles to the family level. The mean number of individuals captured between trap checks declined by 83% between the 1970s and 2010s, and the number of beetle families fell by 39%. Nineteen families had disappeared entirely. Although insect populations normally expand and contract over time, disappearances across whole families are much more unusual. That so many …