Studies from a range of locations have documented declines in insect populations over the last few decades. The majority of these studies are from landscapes that have been subject to land-use change; shifts in land use are thought to be a main cause of insect population declines, along with climate change, increased use of systemic synthetic pesticides, and light pollution. At the Rocky Mountain Biological Laboratory (RMBL), a Malaise trap has been used to collect insects since 1984. The trap location has not moved, and land-use around the RMBL has not changed appreciably since 1984. Most of the landscape surrounding the Malaise trap location is undeveloped native vegetation, with limited seasonal cattle grazing in some areas. Samples were collected 6-19 times per year, for a total of 362 samples, sorted to taxonomic order, and dried and weighed. To look for potential causes of changes in insect populations we combined these data on insect abundance and biomass with data on snowmelt, temperature, precipitation, and floral abundance.
Results/Conclusions
The average trap catch per day has declined significantly since 1984, with larger declines for flies and hymenoptera and no evidence of declines in some other orders. Total insect abundance was negatively affected by temperature and positively affected by summer precipitation, with additional lagged effects of winter snowfall. Insect biomass was negatively affected by a lagged effect of the previous summer’s temperatures. The declines we observed for insect population at the RMBL are despite the lack of major land use change in the area, the absence of agriculture, and low human density. However, summer temperatures have tended to increase at the RMBL, and winter snowfall has tended to decrease, suggesting that climate change has contributed to the decline in insect abundance over the past 36 years.