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Insects have declined by as much as 80%, say entomologists



May 19, 2017

In news that might well be an unwelcome vindication of Rachel Carson’s groundbreaking book, Silent Spring, entomologists in Europe have found the overall biomass of insects in some areas has alarmingly declined by as much 80% in the last 20 years.

Hunches born of anecdotal observations of the dwindling number of splattered bugs on windshields has led to some hard and undeniable data that the biomass of insects in some areas has plummeted sharply in the previous two decades.

While splattered insects on windshield is far from a scientific measure, new longitudinal data has come to light that is charting a worryingly steep decline in insect biomass. The data comes from a group of mainly amateur entomologists who have tracked the populations of less charismatic insect species – hoverlfies, moths, beetles, and bugs – in 100 nature reserves across Western Europe since the 1980s.

The Krefeld Entomological Society in Germany first noticed a large drop off in their overall catch in 2013 and, thinking it could just have been a bad year, they returned to the same site again the following year only to have their observations confirmed. Their overall catch had declined by nearly 80% since they first started keeping records in the late 1980s. They began making comparisons with catches from other areas and found similar declines across more than a dozen other ecosystems.

What their data shows for the first time is that while scientists have been charting the decline of domesticated honey and bumble bee species for decades, the populations of other, less-studied insects may well have been crashing too.

The data from Germany has prompted universities to get involved in an attempt to find the reason why the decline is happening. Changing land use and farming practices have played a roll, but insect populations have also declined in areas where previously farmed land has been allowed to revert to wildflower meadows, increasing floral biodiversity.

A prime suspect is, again, neonicotinoid pesticides, which were introduced in the 1980s. Coincidence?  Dave Goulsen, a UK entomologist based at the University of Sussex, has been working with the Krefeld Entomological Society to analyse and publish their data. His previous research has showed that targeted use of neonicotinoids has significant impacts on non-target species. The solubility of neonicotinoids sees them readily leeching into streams and rivers, as well as finding their way into marginal vegetation surrounding fields where they are applied. Neonic’s propensity to work their way into the wider ecosystem has potentially major ramifications for insects and birds.

The effects of these pesticides on honey bees has been well publicised, leading to several of their active constituents being banned for field use in European Union. Neonicotinoids have been found to affect honey bees’ navigation and communication abilities, playing a roll in the decline of bee populations, but the impact of this class of pesticides on other insects hasn’t been studied and isn’t known.  Given their effect on honey bees, it isn’t much of a stretch of suggest that their effects on other insect species could be just as bad, if not worse than their effect on honey bees.

Whether or not neonicotinoids are a major factor in the decline of insect biomass observed by Krefeld group remains the subject of further study.  To read more about their findings and a good overview of issue more generally, go here.


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