The bug picture
We need more data if we are to build a full picture of global insect decline, say Tim Newbold and Charlotte Outhwaite
Insect declines have hit the headlines several times over the past few years, with suggestions of mass extinctions, or 'insectageddon'. However, some of the underlying science has been questioned for focusing only on the declines, using evidence from specific places to suggest more general trends, and failing to consider that insect populations naturally fluctuate a lot. Moreover, recent work has also uncovered a more mixed picture, with some positive trends.
Certainly, there is a lot of good evidence pointing toward very large declines of insects around the world in recent decades. The total biomass of flying insects in German nature reserves declined by more than three-quarters in less than 30 years, you are around one-third less likely now to see any type of bumblebee in Europe and North America than 50 years ago, and populations of many UK insect groups are on a downward trajectory. Key threats, according to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services's Assessment Report on Pollinators, Pollination and Food Production (bit.ly/2VXcF9Y), include the conversion of land to agriculture, the application of chemicals such as fertiliser and pesticides on this farmland, and climate change.
“In most parts of the world, there are not the sort of long-term monitoring programmes for insects that we have for some mammals and birds“
It is not all bad news, however. A recent study of UK wildlife trends showed that the distribution of freshwater insects has increased in recent years after experiencing strong declines, probably as a result of improvements in UK water quality. Similarly, while the biomass of UK moths has been in steady decline since the 1980s, this has not yet offset increases seen in the 1970s. In the Netherlands, an assessment of national wildlife trends revealed an increase in dragonfly distributions between 1990 and 2014, again probably in part because of improvements in water quality, but also perhaps because dragonflies have benefited from recent climate change. These positive trends should not create complacency, though. Many groups of insects are particularly susceptible to climate change, so as we see greater and greater temperature increases, declines of insects are likely to accelerate.
Missing data
One of the major challenges we face in trying to understand insect declines is a lack of good data. In most parts of the world, there are not the sort of long-term monitoring programmes for insects that we have for some mammals and birds. This lack of data means that we often have to rely on fragmentary evidence to estimate what is happening, hence the uncertainty and debates about studies of insect declines. The UK is fortunate in that insect monitoring has been taking place for a number of decades. There are standardised monitoring schemes, such as the UK Butterfly Monitoring Scheme, and more than 80 other recording schemes collecting data on UK wildlife – including many insect groups. Other parts of the world are much less studied. There is a particularly important gap in tropical regions, which harbour an exceptional diversity of insects that are likely to be particularly sensitive to climate change. These regions are also likely to see a major transformation of natural habitats to farmland during the coming decades.
Despite the lack of good data, it is vitally important that we try to understand insect declines, because there are huge consequences to losing these vital components of our natural systems. Insects provide food for other animals within food webs, recycle nutrients, transform the physical environment, and support plants through pollination and dispersal of seeds (see Figure 1), among countless other roles, many of which we don't fully understand. Many of these functions are also vital for humans, providing so-called 'ecosystem services'. Insect services are particularly important in allowing us to grow our food. Many insect predators help to control populations of other insects that are crop pests, and insects play a vital role in pollinating crops. Quite aside from these tangible material benefits, insects are also culturally very important. While we may be fairly happy to live without mosquitoes, insects such as butterflies and bumblebees are an important part of what we treasure most in the natural world.
Particular concern has been raised in recent years about the plight of pollinators. A 2006 study reported steep declines of pollinators in the UK and the Netherlands during recent decades. In the UK, pollinators are one of the insect groups showing the largest declines. A major international report recently documented the cocktail of threats faced by pollinators, including agricultural intensification and chemical application. Climate change is a growing concern, adding to the many existing threats faced by pollinators. For example, recent declines in bumblebees are strongly linked to climate change. The coming decades will see rapidly increasing temperatures, which will push more and more pollinator species beyond their limits. The loss of pollinators will have major consequences for agriculture. Most estimates suggest that the value of crop pollination alone stretches to hundreds of billions of dollars every year.
“Many insect predators help to control populations of other insects that are crop pests, and insects play a vital role in pollinating crops“
After decades of being relatively under-studied, it is good to see insects and other invertebrates moving up the research and policy agendas. However, we still have a long way to go in our understanding of insect declines, and of the consequences of these declines for wider natural systems. In particular, we need to achieve much deeper knowledge of the many roles that insects play, including those that benefit human societies. While there are some bright spots showing that recovery is possible under the right conditions, the current evidence points to steep declines in most insect groups in most places. Halting and even reversing these declines must be a priority to secure these oft-neglected animals that make such an important contribution to our wellbeing.
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1/3rd You are one third less likely to see a bumblebee in Europe or North Americanow than 50 years ago
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80 There are more than 80 recording schemes collecting data on UK wildlife
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75% The biomass of flying insects in German nature reserves has declined by more than 75% in less than 30 years
Tim Newbold is a senior research fellow, Centre for Biodiversity and Environment Research, Department of Genetics, Evolution and Environment, University College London.
Charlotte Outhwaite is a post-doctoral research fellow, Centre for Biodiversity and Environment Research, Department of Genetics, Evolution and Environment, University College London.