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, and their significant contributions to vital ecological functions including pollination, pest control and maintenance of wildlife cannot be ignored.
But a new scientific review of insect numbers 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. This should concern not only professionals in agriculture but also professionals in health and development as this "plague of pests" could have many detrimental impacts on human health and livelihoods - especially those of the poor who are the most vulnerable. This threat could undermine decades of hard-earned progress in development.
Insect-based ecosystem services such as pollination and pest suppression are essential for agriculture and for the people whose livelihoods depend on it. Insect natural enemies of crop pests keep pest populations in check, reducing the likelihood and frequency of outbreaks and the need for synthetic insecticides, which are known to harm human health and the environment.
Why the decline?
Pesticides use 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 ecosystem services, they also cost money - a burden for resource-constrained farmers in low- and middle-income countries such as those in Sub-Saharan Africa.
The development of insecticide resistance by pest species is a key part of this destructive dynamic. It is likely to further worsen the situation, making insecticides more expensive and possibly more toxic to humans, other organisms, and the environment.
Our recent study describes a feedback loop: If the ecosystem service of 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 biocontrol 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 described as a "pesticide treadmill".
More alarming is the fact that insect crisis is just one among many threats. This is not surprising because 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 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". The report identifies land-use changes, pollution and climate change as causes of biodiversity loss.
How to halt the decline
What can researchers, development practitioners, and policymakers do? More attention should be directed toward three main areas, with efforts pursued simultaneously. First, there is a need to protect natural and semi-natural habitats in agricultural landscapes and beyond. The diverse values 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 are needed to help us understand where their benefits lie. This includes both economic and other benefits, who receives them, and what likely interactions and inter-connections exist among species and across land use types.
More research-for-development work is needed to improve the governance of commons where many of the crucial habitats exist. More urgently, researchers must be more proactive and effective at communicating their findings Innovations in technology and policies need to go alongside public campaigns aimed at influencing cultural change. Second, the adoption of biodiversity-friendly practices should be accelerated.
While becoming more common, these are not growing quickly enough.  CGIAR researchers are well positioned to explore this topic and use their work to inform the public and policymakers on existing obstacles and the technological and institutional innovations needed to accelerate the adoption of ecologically-based practices by farmers at all scales in developing and developed countries.
Third, researchers, development practitioners and policymakers should support farmers to judiciously use synthetic insecticides and other agro-chemicals. The overuse of synthetic insecticides is driven by a number of factors: current 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 available technical support and insurance or other risk management tactics, among others. 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 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.
 Francisco Sánchez-Bayo and Kris A.G. Wyckhuys Worldwide decline of the entomofauna: A review of its drivers (Biological Conservation, April 2019)
 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)
 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)
 Laurie Laybourn-Langton and others This is a crisis: Facing up to the age of environmental breakdown (Institute for Public Policy Research, February 2019)
 The state of the world's biodiversity for food and agriculture (UN FAO, 2019)