Act fast to halt the decline of insect numbers

By Wei Zhang Researchers, policymakers and donors should act fast to halt the diminishing insect...

By Wei Zhang

Act fast to halt the decline of insect numbers
Researchers, policymakers and donors should act fast to halt the diminishing insect numbers, writes Wei Zhang.

Insects are among the most diverse and successful organisms on our planet. Their significant contributions to vital ecological functions including pollination, pest control and maintenance of wildlife cannot be ignored.

But a scientific review of insect numbers published earlier this year startlingly warns that bees, ants and beetles are disappearing eight times faster than mammals, birds or reptiles. Meanwhile, some species such as houseflies and cockroaches are likely to boom.

“Both regulatory and market-based interventions are needed to reduce farmers’ reliance on insecticide-based control in the long run,”

Wei Zhang, International Food Policy Research Institute

This should concern not only professionals in agriculture, but also in health and development. This “plague of pests” could have many detrimental impacts on human health and livelihoods — especially those of the poor. It could undermine decades of hard-earned progress in development.

Why the decline?

Insects provide ecosystem services, such as pollination and pest suppression, which are essential for agriculture and for the people whose livelihoods depend on it. As natural enemies of crop pests, insects reduce the likelihood and frequency of disease outbreaks and the need for synthetic insecticides, known to harm human health and the environment.

The use of pesticides is a major cause of the alarming insect declines outlined in the review. They decimate beneficial insect communities, including those that control pests. Unlike natural pest control, they also cost money — a burden for resource-constrained farmers in low- and middle-income countries such as those in Sub-Saharan Africa.

Pests often develop resistance to insecticides, and this is a key part of a destructive dynamic where insecticides become more expensive and possibly more toxic. A recent study I led describes how the feedback loop works: if biocontrol is effective at crop level, a farmer may refrain from using pesticides, allowing the natural pest enemies to thrive. But if insecticide use is indiscriminate, then natural enemies may not be effective, and their life cycle may be disrupted — ultimately destroying the ecosystem service they provide.

In other words, farmers can develop a ‘lock-in’ syndrome where continued heavy spraying is necessary to compensate for the missing beneficial insects that this same spraying has caused, a syndrome we called the “pesticide treadmill”.

More alarming is the fact that the insect crisis is just one among many environmental threats. This is not surprising. The challenges today’s world faces, as well as their many underlying drivers, are interlinked. A recent report from the Institute for Public Policy Research warns of a potentially deadly combination of factors. These include climate change, mass loss of species, topsoil erosion, deforestation, and acidifying oceans, which are driving a complex, dynamic process of environmental destabilisation that has reached critical levels.

The UN FAO’s new report on biodiversity for food and agriculture, which is based on data gathered in 91 countries, concludes that the plants, animals, and microorganisms that are the bedrock of food production are in decline. If these critical species are lost, it “places the future of our food system under severe threat”, it states. The report identifies land-use changes, pollution and climate change as causes of biodiversity loss.

How to act

What can researchers, development practitioners, and policymakers do? More attention should be directed toward three main areas simultaneously.

First, natural and semi-natural habitats should be protected. The diverse value of these habitats — in providing a wide array of ecosystem services themselves, as well as supporting organisms that provide ecosystem services — should be made more ‘visible’ and accounted for in decision-making.

Valuation and modelling studies should be carried out to help understand where their benefits lie. This goes for both economic and other benefits, who receives them, and how species and different land use types interact. Research is also needed to improve the governance of crucial habitats.

More urgently, researchers must be more proactive and effective at communicating their findings to the public, governments, non-governmental organisations and other key stakeholders. Innovations in technology and policies are needed alongside public campaigns aimed at influencing cultural change.

Second, the adoption of biodiversity-friendly practices should be accelerated. Although now more common, these are not growing quickly enough. Researchers at the CGIAR, a global partnership in which I am a member, are well-positioned to tackle this.

Finally, farmers should be supported to use synthetic insecticides and other agro-chemicals judiciously. The overuse of synthetic insecticides is driven by a number of factors: prices that do not account for the social and environmental costs associated with their use, distorting policies, lack of knowledge and awareness, and an absence of risk management tools such as technical support and insurance. Both regulatory and market-based interventions are needed to reduce farmers’ reliance on insecticide-based control in the long run.

Together, these three strategies can help address the threat posed by the dangerous decline in insect populations. Managing the crop pest problem, so that pests and natural enemies co-exist and sustain a balance resilient to environmental shocks, is our first line of defence.

If this line holds, we can avoid getting to the stage where we are trying to ‘control’ the problem and many of the negative social, economic and environmental consequences associated with our interventions.

Wei Zhang is a research fellow in the Environmental, Production and Technology division of the International Food Policy Research Institute, based in Washington, D.C., United States. She can be contacted at
This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.




[1] Francisco Sánchez-Bayo and Kris A.G. Wyckhuys  Worldwide decline of the entomofauna: A review of its drivers (Biological Conservation, April 2019)
[2] Wei Zhang and others Multidecadal, county-level analysis of the effects of land use, Bt cotton, and weather on cotton pests in China (PNAS, 14 August 2018)
[3] Patrick W Weddle and others History of IPM in California pears—50 years of pesticide use and the transition to biologically intensive IPM (Pest Management Science, 13 October 2009)
[4] Laurie Laybourn-Langton and others This is a crisis: Facing up to the age of environmental breakdown (Institute for Public Policy Research, February 2019)
[5] The state of the world’s biodiversity for food and agriculture (UN FAO, 2019)


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