Major insect pests of rice in Japan have experienced a persistent and substantial decline over the past seven decades, a trend driven primarily by agricultural management practices rather than climatic changes. A new study published in Agriculture & Food Security utilized exceptionally long-term monitoring records to assess the temporal dynamics of eight key insect species. The research indicates that while temperature increases generally showed negative associations with pest abundance, the most significant suppressive effects came from pesticide use and land consolidation. This finding challenges the widespread concern that global warming is inevitably creating more favorable conditions for agricultural pest outbreaks in Japan.

The study, led by researchers including Takehiko Yamanaka, Shigeki Kishi, and Sunao Ochi, employed an empirical dynamic modeling framework to analyze data from 16 study sites across the Hokuriku, Chugoku, and Shikoku regions. These sites were selected because they contained continuous monitoring records for all eight target insect rice pests spanning more than 30 years, with some time series extending up to 71 years. The monitoring protocol, standardized since 1946, involves the use of bucket-style light traps equipped with 60-watt incandescent lights near conventionally managed rice paddies. Insects are collected daily, identified by entomologists, and summarized at five-day intervals from April to October, providing a robust dataset for long-term causal analysis.

The eight focal species include lepidopteran stem borers such as Chilo suppressalis and Nymphula aenescens, the dipteran Tipula aino, and several hemipteran leafhoppers and planthoppers, including Nephotettix cincticeps, Recilia dorsalis, Sogatella furcifera, Laodelphax striatellus, and Nilaparvata lugens. These pests have historically been central targets of crop protection in Japan, where rice is the most important staple grain. Prior to the widespread use of synthetic pesticides after World War II, these insects caused significant damage to rice leaves and ears. The study aimed to disentangle the simultaneous effects of climate change and management interventions, which have operated concurrently over decades, to determine which factors have dominated long-term population trends.

Using nonmetric multidimensional scaling to visualize temporal trends, the researchers found that insect rice pests were highly prevalent before the 1960s, with an integrated abundance index of 2.81 in the 1950s. This index decreased monotonically over the following decades, reaching a value of 1.03 in the 2010s. Because the index is on a logarithmic scale, this change corresponds to an approximately 60-fold reduction in insect rice pest abundance over 60 years. The analysis revealed that while most species showed steady declines, some exhibited irregular fluctuations. For instance, Nymphula aenescens declined monotonically until the 1980s but showed occasional increases after the 1990s, while Recilia dorsalis experienced sporadic outbreaks in the 1990s and 2010s despite an overall downward trend.

The causal analysis, conducted using convergent cross mapping and multiview distance regularized S-map models, identified agricultural management practices as the primary drivers of these declines. Neonicotinoid pesticides, particularly when applied in nursery boxes, showed the strongest negative relationships with hemipteran pests such as Nephotettix cincticeps, Sogatella furcifera, and Nilaparvata lugens. The introduction of plastic nursery boxes in the 1970s allowed for the use of systemic compounds that provided prolonged protection to transplanted seedlings, effectively suppressing early infestations. Land consolidation, a national initiative launched in 1963 to promote mechanized farming, also exerted significant ancillary management effects. Consolidated paddies dry out during winter, reducing the survival of overwintering insects, and the use of mechanized combines further reduced pest populations by cutting mature rice stems at the base.

In contrast, the effects of climate change were generally weaker and more species-specific. Increases in temperature, including the number of days with maximum temperatures exceeding 35.0 degrees Celsius, showed negative associations with the abundances of several migratory hemipteran pests. However, these climatic effects were less pronounced than those of pesticides and land consolidation. For example, spring temperature was negatively related to Chilo suppressalis and Nymphula aenescens, while autumn temperature showed a positive association with Nymphula aenescens, consistent with its preference for humid conditions. Precipitation effects were variable and did not show clear long-term trends across the study regions, making it difficult to resolve their long-term impact on pest populations.

The study highlights the effectiveness of integrated pest management in Japan, which combines physical pest-prevention measures with adaptive pesticide use guided by regular monitoring. Although the combination of adaptive pesticide selection and large-scale changes in paddy field structure was not deliberately designed as a unified IPM system, it has functioned effectively to maintain pest populations at low densities. The widespread use of neonicotinoids and fipronil in nursery boxes is regarded as a best practice in Japanese IPM because it reduces overall pesticide inputs and enhances environmental safety. However, the study notes that severe resistance to these chemicals has been observed in Nilaparvata lugens and Sogatella furcifera since the 2000s, prompting the use of newer, more environmentally friendly pesticides such as flupyrimin and chlorantraniliprole.

Regional differences in pest composition were observed, with Shikoku having more hemipteran rice pests due to its southwestern location, which receives a higher influx of migratory species from southern China. Hokuriku, facing the Japan Sea, historically experienced more severe damage from lepidopteran pests. These geographic tendencies were consistent with the findings of the nonmetric multidimensional scaling analysis. The study also acknowledges limitations, including the restriction to Japan, which may limit extrapolation to other agroecosystems, and the use of light-trap records as proxies for field-level population densities. Pesticide sales were used as proxies for application intensity, which may not precisely capture local exposure, and the long-term trends in the data can sometimes impair the reconstruction of nonlinear dynamics in causal inference.

Despite these limitations, the study provides a parsimonious explanation for the observed patterns, emphasizing the dominant role of anthropogenic factors in shaping pest populations. The findings are consistent with independent nationwide data indicating a long-term decline in major insect rice pests in Japan, attributed to agricultural intensification. The research underscores the importance of long-term, multi-site, and multi-species datasets for disentangling the complex interactions between climate and management practices. As global warming continues, the study suggests that continued monitoring and adaptive management will be crucial to mitigating widespread pest outbreaks and ensuring food security in rice-producing regions.

The study also compares Japan’s experience with other Asian countries, noting that insect rice pests have declined in many monsoon Asian regions due to the adoption of multi-resistant rice varieties and improved crop management. In contrast, China has seen an increase in insect rice pests since the 1970s, largely due to heavy reliance on chemical pesticides and the lack of widespread IPM implementation. The Japanese case demonstrates that a balanced approach to pest management, combining chemical control with structural changes in agricultural practices, can lead to sustainable suppression of pest populations. This integrated framework, supported by sustained national pest monitoring, offers valuable insights for other regions seeking to manage agricultural pests effectively in the face of climate change.

The empirical dynamic modeling framework used in this study offers a distinct methodological advantage over traditional linear time-series approaches. By reconstructing nonlinear system dynamics directly from the data, the model accommodates non-stationarity and long-term trends without assuming time-invariant parameters. This approach allows for the detection of directional causal associations that correlation-based or forecast-based linear methods often fail to capture. The researchers applied convergent cross mapping to infer these causal links, assessing significance by verifying that prediction skill increased with library size and exceeded that of surrogate data. This rigorous testing helps address the challenge of disentangling simultaneous drivers, such as climate and management, which have operated concurrently for decades.

Specific chemical classes played distinct roles in the observed population shifts. While neonicotinoids and fipronil were effective in suppressing hemipteran pests, organochloride pesticides were associated with increased abundances of certain species, such as Nephotettix cincticeps and Laodelphax striatellus. This counterintuitive result may reflect the elimination of natural predators by organochlorides during the 1960s, a period when these chemicals were widely used before being banned due to their environmental persistence and bioaccumulation potential. The subsequent reduction in organochloride applications and the adoption of alternative pesticides allowed natural predator populations to persist, contributing to more stable pest control. This historical shift underscores how the spectrum of insecticides used over time can influence the long-term trajectory of pest populations.

The study’s findings align with broader trends observed across monsoon Asia, where insect rice pests have generally declined since the 2000s in countries such as India, Thailand, and Indonesia. This regional decrease is partly attributed to the widespread use of neonicotinoids and fipronil, although these chemicals are often sprayed directly onto paddy fields rather than applied in nursery boxes. However, the emergence of pesticide resistance and recurrent pest resurgences associated with these compounds has been reported in these regions. In Japan, the specific practice of applying these systemic compounds in nursery boxes has been regarded as a best practice in integrated pest management, as it minimizes impacts on surrounding biota while effectively controlling early infestations. This distinction highlights how application methods can influence both efficacy and environmental safety.

Despite the overall success of these management strategies, the study notes that concerns about new pest species remain. The rice-water weevil, an invasive species originating from California, spread across Japan in the 1980s but was effectively managed with pesticides. More recently, rice bugs have become a serious issue in northern Japan, particularly after the 2000s, because their populations persist in surrounding grasslands and repeatedly migrate into paddy fields. While rice stink bugs compromise grain quality, their impact on overall yield is limited. These examples illustrate that while major historical pests have been suppressed, the agricultural landscape continues to face challenges from emerging threats that require adaptive management strategies.

Subject of Research: Long-term trends in insect rice pest populations in Japan and the impact of management practices and climate

Article Title: Persistent decline of major insect rice pests in Japan over 70 years

Article References: Yamanaka, T., Kishi, S., & Ochi, S. (2026). Persistent decline of major insect rice pests in Japan over 70 years. Agriculture & Food Security, 15(1), Article 60.

Published Date: November 11, 2026