Insect decline much less dramatic than claimed

The decline in the number of insects is much less rapid than was stated by scientists a few years ago. The percentage does not fall by 3% per year, but by 1%.

This is apparent from a new scientific publication that has appeared in the scientific journal Science. In the treetops and in the water, the amount of insects even increases. However, there appear to be very large variations locally. The study was conducted by researchers from the German Center for Integrative Biodiversity Research (iDiv), Leipzig University and Martin Luther University Halle-Wittenberg.

Insect apocalypse
In recent years, a number of studies have been published showing a dramatic decline in insect numbers over time. The most prominent, from nature reserves in West Germany, suggested a remarkable decrease in flying insect biomass (>75% decrease over 27 years). This was published in 2017, sparking a media storm suggesting a widespread "insect apocalypse." Since then, several follow-up publications have appeared from all over the world. Usually a strong decrease was described, others less and some publications even mentioned an increase.

166 long-term studies
So far, no one has combined the available data on insect abundance trends around the world to examine how widespread and severe the insect decline is. The researchers of this latest report do pretend to have formed a complete picture. Scientists collaborated internationally for this study to collect data from 166 long-term surveys conducted between 1925 and 2018 at 1676 locations around the world.

Local big differences
The analysis revealed a wide variation in trends, even between nearby locations. For example, in countries where many insect surveys have taken place, such as Germany, the United Kingdom and the United States, some places have experienced a decline, while other nearby sites showed no changes or even an increase.

Combining all trends worldwide, the researchers found that the amount of insects such as butterflies, insects and ants on land decreased over time by an average of 0,92% per year. Much less than the 3% per year, which started ringing alarm bells a few years ago and put pesticides under a magnifying glass.

Turning the tide
According to the researchers, the figures also show that the negative trend can be reversed. In the past 50 years, various measures have been taken in many places in the world to tackle polluted rivers and lakes. This may have enabled the recovery, the researchers write.

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