Insect numbers in west German nature reserves have fallen by more than 76% in just 27 years, according to a new study. The fall was even higher in the summer months, with 82% on average fewer insects being recorded. It is not just vulnerable species such as bees, butterflies and moths that are at risk: all flying insects have been affected. The reasons for this dramatic fall are unclear.
The researchers ruled out changes in weather, plant cover and local landscape playing a significant role in the observed decline, but suggest that intensive agriculture and pesticides in fields near to the reserves could be responsible.
Science for Environment Policy explains, 19 July 2018.
Whatever the cause, the catastrophic fall in insect numbers will inevitably lead to knock-on effects on ecosystems in the long term, particularly due to their essential role as pollinators and their position in the food web. The researchers say that preserving and protecting insects should now be a priority for conservation policies.
Global declines in insects have sparked wide interest among scientists, politicians, and the general public. Loss of insect diversity and abundance is expected to provoke cascading effects on food webs and to jeopardize ecosystem services. Our understanding of the extent and underlying causes of this decline is based on the abundance of single species or taxonomic groups only, rather than changes in insect biomass which is more relevant for ecological functioning. Here, we used a standardized protocol to measure total insect biomass using Malaise traps, deployed over 27 years in 63 nature protection areas in Germany (96 unique location-year combinations) to infer on the status and trend of local entomofauna. Our analysis estimates a seasonal decline of 76%, and mid-summer decline of 82% in flying insect biomass over the 27 years of study. We show that this decline is apparent regardless of habitat type, while changes in weather, land use, and habitat characteristics cannot explain this overall decline. This yet unrecognized loss of insect biomass must be taken into account in evaluating declines in abundance of species depending on insects as a food source, and ecosystem functioning in the European landscape.