# Potential Geographic Distribution and Suitable Area of Three Species of Diabrotica (Coleoptera: Chrysomelidae) Beetles in Corn-Planting Regions of China

## TL;DR

This study predicts the potential spread of three invasive corn beetles in China and highlights the risk they pose to corn crops.

## Contribution

The study provides a novel assessment of the invasion risk of Diabrotica beetles in China using bioclimatic variables and corn distribution data.

## Key findings

- D. undecimpunctata and D. virgifera virgifera have large potential suitable areas in China, while D. barberi has a small one.
- Under future climate scenarios, high-suitability areas for D. undecimpunctata and D. virgifera virgifera are expected to decrease.
- The beetles pose a high invasion risk in China's corn-planting regions due to their large potential suitable areas.

## Abstract

The Diabrotica beetles of D. virgifera virgifera, D. undecimpunctata, and D. barberi are important insect pests of corn crops that natively occur in America and are mainly distributed between 35–49° N. In addition, they have spread rapidly to many countries in Europe over the past 70 years since 1955. Corn is also one of the main crops in China; its planting area is mainly distributed between 30–50° N, and these geographical latitudes are similar to those of America and Europe. Once they invade into China, it is very likely that they will spread, settle, and develop rapidly in China. So, there is an invasion risk because these Diabrotica beetles can be naturally or anthropogenically transmitted into China. In this study, the potential geographic distribution of these Diabrotica beetles based on their global distribution samples and relevant bioclimatic variables was estimated, and an overlay analysis was further carried out in combination with the actual distribution of corn-growing regions in China, in order to assess their potential invasion risks, especially in the corn-planting regions of China, and in order to service the early warning and management of invasive crop pests under global warming.

Corn rootworms of Diabrotica virgifera virgifera Le Conte, 1868; Diabrotica undecimpunctata howardi Barber, 1947, and Diabrotica barberi R.F. Smith & Lawrence, 1967 are important pests of corn crops that natively occur in America and have a potential risk of spreading into China through natural spreading or anthropogenic invasion. In this study, the potential geographic distribution and suitable area of these three Diabrotica species based on their global distribution samples and relevant bioclimatic variables were estimated, and an overlay analysis was further carried out in combination with the actual distribution of corn-growing regions, especially in China, in order to assess the potential invasion risks of these Diabrotica beetles, especially in the corn-planting regions of China. The results indicated that six bioclimatic variables (i.e., bio2 (mean diurnal range), bio4 (temperature seasonality), bio5 (max temperature of the warmest month), bio6 (min temperature of coldest month), bio13 (precipitation of wettest month), and bio14 (precipitation of driest month)) were selected for the analysis of the potential geographic distribution and suitable areas of these Diabrotica beetles. The suitable area ranges of D. undecimpunctata and D. virgifera virgifera are relatively large in China, i.e., 21.01–48.46° N and 74.01–131.26° E for D. undecimpunctata and 21.58–41.42° N and 78.71–124.43° E for D. virgifera virgifera, respectively, while D. barberi occupies only a small area in China, i.e., 34.21–46.81° N and 108.80–133.75° E. Based on the overlay analysis of the potential geographic distribution of these three Diabrotica species and the actual distribution of corn-growing regions in China, D. undecimpunctata and D. virgifera virgifera have the largest potential geographic distribution areas, totaling 2.618 × 107 ha and 1.814 × 107 ha in 22 and 20 provinces respectively, while D. barberi has the lowest potential geographic distribution area just in 8 provinces, totaling 44.37 × 104 ha, indicating a low-suitability area. Moreover, under the four climate scenarios (i.e., SSP1_2.6, SSP2_4.5, SSP3_7.0, and SSP5_8.5) in the 2030s and 2050s, these Diabrotica beetles have the potential for sporadic increases or decreases surrounding the potential suitable areas under the current scenario. However, it is worth noting that the high-suitability areas of D. undecimpunctata and D. virgifera virgifera decreased, and their medium- and low-suitability areas increased accordingly. It is presumed that Diabrotica beetles, especially D. virgifera virgifera and D. undecimpunctata, have a high risk of potential invasion into China because there is a large potentially suitable area distribution for their possible occurrence in the maize-planting regions of China.