# Integrating Morphological, Molecular, and Climatic Evidence to Distinguish Two Cryptic Rice Leaf Folder Species and Assess Their Potential Distributions

## TL;DR

This study uses morphological, genetic, and climate data to distinguish two similar rice pests and predict their future spread under climate change.

## Contribution

The study integrates morphological, molecular, and climatic data to clarify the distinction and potential distribution of two cryptic rice leaf folder species.

## Key findings

- C. patnalis causes more severe field damage than C. medinalis despite their morphological similarity.
- The MaxEnt model predicts suitable habitats for C. medinalis and C. patnalis based on precipitation patterns.
- Climate change is expected to increase the risk of infestation by both species, particularly C. patnalis.

## Abstract

At present, infestations by Cnaphalocrocis patnalis Bradley (Lepidoptera: Crambidae) are showing an increasing trend, yet monitoring efforts remain primarily focused on Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae). In the context of ongoing climate change, reducing monitoring discrepancies between C. medinalis and C. patnalis is of critical importance for improving pest surveillance and addressing existing research gaps regarding these two species. Accordingly, the MaxEnt model was employed to predict and analyze the potential geographic distributions of C. medinalis and its closely related species C. patnalis based on known occurrence records and climatic variables. The model performance was ≥0.9, indicating “good fit” predictive precision. Morphological observations and population dynamics analysis demonstrated that the two species are morphologically similar. Genetic analysis revealed differences in the COI gene fragment, confirming that they are closely related species. Nevertheless, C. patnalis causes more substantial damage in the field compared to C. medinalis. Moreover, the difference in their peak occurrence times is minimal. The MaxEnt results suggest that the distribution of C. medinalis may be suitable in regions between 20° N and 40° N, especially in most parts of southern Eurasia, while C. patnalis may be suitable in coastal regions near the equator. The precipitation of the wettest month is the primary factor influencing their distribution. Under future climate change scenarios, although low-suitability areas are extensive, the suitable area for both species, particularly C. patnalis, reaches its peak in the SSP245 scenario, covering 2.87% of the total land area, indicating a potential risk of occurrence. Based on these findings, the implementation of monitoring and control measures for C. medinalis and C. patnalis is recommended to ensure the safe production of rice.

The larvae and damage symptoms of Cnaphalocrocis medinalis and Cnaphalocrocis patnalis exhibit a high degree of similarity, which often leads to confusion between the two species. This has posed challenges for research on their population dynamics and the development of effective control measures. To better understand their morphological and damage characteristics, population dynamics, species identification based on COI gene fragments, and potential future distribution, a searchlight trap monitoring program was conducted for C. medinalis and its closely related species C. patnalis across four sites in Longhua, Haitang, and Yazhou districts in Hainan Province from 2021 to 2023. The MaxEnt model was utilized to predict the potential global distribution of both species, incorporating known occurrence points and climate variables. The trapping results revealed that both species reached peak abundance between April and June, with a maximum of 1500 individuals captured in May at Beishan Village, Haitang District. Interannual population fluctuations of both species generally followed a unimodal pattern. Genetic analyses revealed distinct differences in the mitochondrial COI gene fragment, confirming that C. medinalis and C. patnalis are closely related yet distinct species. The population peak of C. patnalis occurred slightly earlier than that of C. medinalis, and its field damage was more severe. Infestations during the booting to heading stages of rice significantly reduced seed-setting rates and overall yield. Model predictions indicated that large areas of southern Eurasia are suitable for the survival of both species, with precipitation during the wettest month identified as the primary environmental factor shaping their potential distributions. At present, moderately and highly suitable habitats for C. medinalis account for 2.50% and 2.27% of the global land area, respectively, whereas those for C. patnalis account for 2.85% and 1.19%. These results highlight that climate change is likely to exacerbate the damage caused by both rice leaf-roller pests, particularly the emerging threat posed by C. patnalis. Overall, this study provides a scientific basis for invasion risk assessment and the development of integrated management strategies targeting the combined impacts of C. medinalis and C. patnalis.