The fall armyworm, Spodoptera frugiperda, is a multivoltine moth native to the Americas whose larvae devour an extraordinary range of vegetation, including economically critical crops such as corn, sorghum, and sugarcane. Since 2016, the species has invaded numerous countries across Africa, Asia, and Oceania, cementing its reputation as one of the world’s most destructive agricultural pests. Its population dynamics follow dramatic boom-and-bust cycles, and a key driver of those crashes is a naturally occurring pathogen: Spodoptera frugiperda multiple nucleopolyhedrovirus, or SfMNPV. This species-specific baculovirus is lethal to the armyworm and has even been deployed as a biopesticide. When a larva ingests viral occlusion bodies — protein-encased packages of double-stranded DNA visible under a light microscope — the virus proliferates inside its body until the larva literally liquefies, splattering virus-laden fluid onto the foliage where other larvae feed and continue the infection cycle.

But there is a second, darker route of transmission: cannibalism. Fall armyworms are notoriously cannibalistic, particularly in their later larval stages, and when a healthy larva consumes an infected conspecific, it risks swallowing a lethal dose of virus along with the meal. Researchers at the heart of the new study, led by Kale Rougeau and Bret Elderd, wanted to know how two major climate change stressors — rising temperature and declining resource quality — might alter this cannibalistic behavior and, in turn, the spread of disease. Rather than testing each stressor in isolation, they designed a fully factorial experiment combining three temperature regimes, four diet treatments, and two infection statuses, for a total of 480 individual larvae across 24 treatment combinations.

The temperature treatments were carefully calibrated using a thermal performance curve for the species. A cooler regime of 26°C days and 16°C nights approximated the armyworm’s thermal minimum, an optimal regime of 31°C and 21°C matched its thermal optimum, and a warmer regime of 34°C and 26°C sat just below its thermal maximum. To simulate the nutritional consequences of climate change, the team manipulated the protein-to-carbohydrate ratio of artificial diets. Rising atmospheric carbon dioxide dilutes nitrogen in plant tissue, lowering the protein available to herbivorous insects — a phenomenon known as nutrient dilution. The researchers created a high-protein diet with a 5:1 protein-to-carbohydrate ratio, an equal 1:1 diet, and a low-protein 1:5 diet, alongside a standard commercial diet as a baseline. Larvae fed their assigned diet for one full instar before entering the behavioral trials.

The experimental setup was elegantly simple. Fourth-instar larvae, starved for 24 hours, were placed in Petri dish arenas with either an infected or uninfected third-instar conspecific and a cube of their assigned diet. Infected conspecifics had received a lethal dose of 1 × 10⁵ SfMNPV occlusion bodies per microliter, and verification larvae confirmed that 100 percent of infected individuals died of viral liquefaction while no uninfected controls showed contamination. The arenas were checked for cannibalism at 1, 2, 4, 8, 16, and 24 hours, and surviving fourth instars were then reared through pupation so the team could measure fitness via pupal mass, a well-established proxy for fecundity in this species.

The results were striking. Cannibalism rates climbed steadily with temperature across every diet type, and the best-fit statistical model — selected using the small-sample-corrected Akaike Information Criterion — included a three-way interaction among temperature, diet, and conspecific infection status, accounting for 67 percent of the cumulative model weight. Temperature carried a significant positive effect, with a slope of 0.307 and a p-value below 0.0009. Larvae on the low-protein diet showed the highest overall odds of cannibalism, suggesting they were supplementing missing protein by eating their neighbors. Intriguingly, at cooler temperatures on the low-protein diet, infected conspecifics were cannibalized less readily than healthy ones — yet on the standard diet, infected individuals were more likely to be eaten regardless of temperature. Behavior, it turns out, depends on the full environmental context, not any single stressor.

What about disease? Among larvae that actually cannibalized infected conspecifics, temperature alone best predicted whether infection took hold, with a significant but modest positive slope of 0.117 — roughly one-third the size of the temperature effect on cannibalism itself. Only two individuals across all treatments became infected without consuming their conspecific, likely through trace viral contamination, and these were excluded so the analysis focused purely on cannibalism-driven transmission. The relatively weak direct effect of temperature on infection risk may reflect a biological quirk: each time a larva molts, it sheds the lining of its midgut, expelling recently consumed viral particles before the infection can establish. At higher temperatures, faster development and more frequent molting may partially counterbalance the elevated metabolic costs that otherwise leave insects more vulnerable to lethal infection.

The fitness results added another layer of nuance. Among the 199 moths that successfully eclosed, pupal mass declined with warming temperatures on all macronutrient-manipulated diets but remained stable on the standard diet, and the temperature-by-diet interaction model captured 85 percent of the model weight. Counterintuitively, larvae on the low-protein diet achieved the highest pupal masses — averaging about 184 milligrams compared with roughly 123 milligrams for high-protein larvae — possibly because cannibalism conferred a nutritional advantage to protein-deprived individuals. Notably, neither cannibalism status nor the infection status of the consumed conspecific predicted pupal mass, indicating no detectable fitness cost from sub-lethal viral loads among survivors.

The broader implications are twofold. First, as climate change brings more extreme heat and carbon-driven nutrient dilution degrades plant quality, cannibalism in fall armyworms — and perhaps in other readily cannibalistic herbivorous insects — is likely to increase, driven by a combination of heightened energy demands and protein scarcity. Second, because cannibalism is a transmission route for pathogens, more cannibalism could mean more disease spread, compounded by a slight direct increase in infection risk from temperature alone. Yet the picture is not uniformly grim for the virus: eating an infected conspecific does not always lead to infection, so cannibalism can also remove pathogens from a population. The study’s authors point out that contrasting systems behave differently — warmer temperatures reduce viral transmission in gregarious western tent caterpillars, which disperse rather than congregate in the heat, and diminish fungal infection in spongy moths under warmer, drier conditions.

What happens next for the fall armyworm may depend on geography as much as biology. Climate projections suggest the pest will proliferate in some regions while facing local extinction in areas already near its critical thermal maximum. Changes in cannibalistic behavior and baculovirus transmission could further shape how the species spreads globally, altering both the intensity of crop damage and the efficacy of viral biopesticides. The research team suggests that field experiments and in silico modeling of these coupled dynamics are natural next steps. For now, the message is clear: climate change does not simply make the world hotter — it makes hungrier, more desperate creatures out of the insects that threaten our food supply, and in doing so, it quietly redraws the map of disease.

Subject of Research: Effects of temperature and diet quality on cannibalism and baculovirus transmission in fall armyworm larvae

Article Title: We Are Dying to Eat You: Cannibalism and Disease Transmission Under Global Climate Change

Article References: Rougeau, K., & Elderd, B. D. (2026). We Are Dying to Eat You: Cannibalism and Disease Transmission Under Global Climate Change. Ecology and Evolution, 16(10), Article e74403. https://doi.org/10.1002/ece3.74403

Image Credits: AI Generated

DOI: 10.1002/ece3.74403

Keywords: fall armyworm, cannibalism, baculovirus, climate change, disease transmission, nutrient dilution, insect behavior, host-pathogen dynamics, agricultural pest, pupal mass, temperature, ecology