When an Odd Moth from the Americas Flies into China’s Maize Fields
I knew he meant no offence, and he wasn’t the sort to gloat. The teasing in his tone carried something closer to sardonic mockery of the reality he had come to know.
A few years earlier, he had been running a farm in Heyuan, Guangdong, when one of the “lads” doing aerial drone spraying mentioned that a ferocious pest had appeared in the maize field. It took a very heavy dose of pesticide to kill them — and part of that field grew fresh sweetcorn meant for people to eat.
From then on, Lao Lei made a point of never buying maize from outside, but he thought little of the pest itself, hadn’t even bothered to remember its name. It wasn’t until two years later, when he returned to his hometown in Liuzhou, Guangxi, that he crossed paths with the same insect again, this time in his own maize field. His fellow villagers told him it was precisely during the two years he had been away that the Fall armyworm had overrun their village.
“From what I remember, maize used to need hardly any spraying at all. Now that this pest is around, you definitely have to spray more — at least six rounds of pesticide per maize crop. It takes roughly one jug’s worth of spray per mu of land.” This close-quarters encounter was what finally gave him a true sense of how formidable the Fall armyworm really is. “The most infuriating thing about this pest is that it eats the whorl of your maize, so you have to start spraying at intervals from the seedling stage. Otherwise the maize gets devoured within a week of emerging. Skip the spraying and you might as well kiss the harvest goodbye.”
II. Climate Change: The “Pesticide Treadmill” Speeds Up
The Fall armyworm that has invaded China feeds primarily on maize. Last September, during a door-to-door survey in Yanta Village on the outskirts of Kunming, Yunnan, merely mentioning the Fall armyworm was enough to set the villagers’ brows furrowing and their eyes sharpening.
By the aunties’ and uncles’ estimates in Yanta Village, the Fall armyworm could reduce maize yields by 10–15%, and in severe years even wipe out the harvest entirely — a picture strikingly similar to what Lao Lei described. One auntie said: “There were always pests in the old days, like aphids and springtails, and one round of pesticide was enough. But when the Fall armyworm first turned up, the usual pesticides had no effect at all. We just didn’t know what to do.”
And that is precisely the problem. The “insect pit” bred by decades of heavy pesticide use in the Americas’ intensive agriculture had forged the Fall armyworm’s formidable chemical resistance — one reason it was able to sweep across continents in just a few years. People use the image of a “treadmill” to describe the vicious cycle of over-reliance on pesticides: once the insects develop resistance, farmers spray more pesticide, until the bugs become immune to everything, prompting a scramble to develop a new active ingredient. The Fall armyworm is a living case in point. Having already posed a grave threat to global food production, it triggered a Global Joint Action on Fall Armyworm launched by the Food and Agriculture Organization of the United Nations (FAO), yet even that has failed to stem the insects’ relentless advance.
And just as humanity found itself at its wit’s end in the face of the Fall armyworm, climate change was already pressing the accelerator on the “pesticide treadmill.”
Generally speaking, rising temperatures favour the migration of pests to higher latitudes and altitudes. A single degree Celsius of warming increases losses in wheat, rice, and maize attributable to pest damage by 10–25%. The Fall armyworm is no exception: it thrives in warm conditions, and its development rate accelerates markedly as temperatures climb. Research projections indicate that under global warming the Fall armyworm’s suitable habitat range in China will expand further. The record heat and drought that Yunnan experienced in 2019 likely played a key role in accelerating the insect’s growth, boosting its reproductive rate, and triggering a sudden surge in population size.
III. “Skip the Spraying and You’ll Lose Everything Down to Your Underpants”
Like most farmers, this is exactly what Lao Lei does. Despite years of experience in ecological farming and a working knowledge of insect-repelling enzyme preparations for pest control, he too has had to compromise on this one.
“If even the chemicals can’t deal with those bugs, an enzyme repellent is surely hopeless.” In his own kitchen garden, Lao Lei insists on spraying nothing at all, but the consequence is that Fall armyworm burrow into his chillies and gnaw away at them, and within a day or two the peppers are rotting on the ground.
So while Lao Lei won’t buy fresh sweetcorn from outside, he does have sympathy for that large-scale grower in Guangdong: “Unless you’re just playing about, you can’t blame them. Over a hundred mu of land, so much invested — who would dare skip the spraying?”
Because decades of pesticide overuse have already caused severe environmental and health impacts, China launched a pesticide reduction plan in 2015. The difficulty in controlling Fall armyworm, therefore, lies in suppressing the pest population and safeguarding food production while keeping pesticide use from increasing further.
Since the Fall armyworm first invaded China, the government has poured in substantial dedicated funding, mobilised agricultural researchers nationwide, and incorporated the pest into a monitoring and early-warning network spanning more than 3,000 agricultural counties, working to hold back its northward advance. The Ministry of Agriculture and Rural Affairs publishes an annual technical plan for Fall armyworm control, with core measures encompassing ecological regulation (leveraging farmland biodiversity through insect-resistant and tolerant varieties, intercropping and relay cropping, and trap plants planted along field margins), seed treatment, physical and chemical trapping, biological control, and judicious pesticide use. Some experts recommend prioritising physical and biological control methods, resorting to chemical sprays only as a last resort.
In provinces such as Guangxi, Yunnan, and Henan, biological control methods are being developed and rolled out to counter the Fall armyworm’s steadily strengthening resistance to chemical pesticides. These include introducing natural enemies such as parasitoid wasps, predatory bugs, and parasitic flies, as well as the research, demonstration, and wider adoption of biopesticides based on Metarhizium anisopliae, Beauveria bassiana, and nucleopolyhedrovirus preparations.
The Fall armyworm certainly gives farmers that kind of urgency — not only because of its insecticide resistance but also because of its extraordinary reproductive and dispersal capacity. Its biological traits have been summed up as “exceptionally good at flying, eating, and breeding.” In Lao Lei’s words: “If today you find Fall armyworm on one maize plant and do nothing about it, in two days every nearby plant will be crawling with them, and in two more days that whole field is a write-off. So the moment you spot them, you have to spray immediately.”
The aunties and uncles in Yunnan have been equally plagued by this problem. When Fall armyworm first arrived in Yunnan, they found that the bugs they killed today were replaced by new ones flying in from nearby the very next day. Things only improved after the government brought in professional teams to spray the entire affected area in a unified effort. This is called “coordinated area-wide pest management” — unified spraying by professional operators to combat outbreak-level pests and diseases. Otherwise, if smallholders just “sweep the snow in front of their own door,” they end up having to spray more frequently, and the pests develop resistance all the faster.
But coordinated area-wide pest management is suited to large-scale monoculture growing areas, and smallholders may not necessarily enjoy that “perk.” In Yunnan Province, for example, agricultural expert Li Chunliang believes coordinated spraying is difficult to achieve for smallholders. If the crop is forage maize, smallholders’ plots tend to be scattered, making unified spraying impractical. If the crop is fresh-eating maize, the pesticide dosage required varies across different growth stages, so spraying blindly is even less advisable.
In these circumstances, Li Chunliang believes the only option is to teach smallholders the skills of judicious pesticide use — selecting the right products, rotating active ingredients — so they can manage pests without relying on so many chemicals.
And honestly, farmers don’t want to spray this much either. By Lao Lei’s calculations, the pesticide cost per mu has now risen to around 200 yuan, and in many cases smallholders actually lose money growing maize.
IV. What’s Spreading Isn’t Just the Bugs
At the end of 2023, the Ministry of Agriculture and Rural Affairs granted operating licences for GM maize and soybean seeds to 26 companies, and in 2024 issued a further batch of biosafety certificates for genetically modified organisms, marking the beginning of full-scale GM seed adoption in China. The previous year was thus hailed as China’s “Year One of GM Commercialisation.” Accordingly, the 2024 technical plan for Fall armyworm control introduced a timely new measure: “prioritise insect-resistant GM maize.”
However, a Fall armyworm control guide published by the Food and Agriculture Organization of the United Nations (FAO) cautioned that it is too early to draw firm conclusions about whether GM maize can control Fall armyworm: “Bt maize has been shown to reduce damage caused by Fall armyworm, but Fall armyworm populations in the Americas have already developed resistance to certain Bt maize varieties.” (Note: Bt refers to Bacillus thuringiensis, a beneficial insecticidal microorganism found widely in soils around the world. Scientists have transferred the gene encoding the insecticidal protein from Bt into maize, enabling the plant to produce this protein itself. Since commercial cultivation was approved in the United States in 1996, Bt maize has been widely grown across many countries.)
But Lao Lei now sprays his maize six times a season where once one round sufficed; scientists are sprinting to develop new pesticides, locked in a race against the insects; and in the end the only card left to play is rewriting the genes in the seed — is this the kind of adaptation we want to see?
And this is precisely what gives cause for alarm: not every attempt to meet a crisis with technology brings good results. Looking back over the past several decades at the Fall armyworm’s ever-escalating resistance, a pattern seems to confirm a sobering truth: humanity’s quest for certainty in production through the mastery of nature has bred an ecological crisis that leaves us inhabiting an ever more uncertain world. We cannot help but ask: will the “pesticide treadmill” run forever? And when it finally stops, in what manner will it come to a halt?
References
https://d.wanfangdata.com.cn/periodical/rdzwxb201906028
http://www.ere.ac.cn/cn/article/pdf/preview/10.19741/j.issn.1673-4831.2019.0487.pdf
https://www.fao.org/fall-armyworm/monitoring-tools/faw-map/en/
http://journals.caass.org.cn/zgnxtb/CN/10.11924/j.issn.1000-6850.casb20191100857
http://www.moa.gov.cn/nybgb/2022/202212/202301/t20230104_6418252.htm
https://www.sciencedirect.com/science/article/pii/S2351989421005448
Editor: Ling Yu