1. Introduction
Paederus fuscipes Curtis, 1826, belongs to the Coleoptera order, Staphylinidae family, and
Paederus genus (Fabricius, 1775). It is a predatory insect and a natural enemy of agricultural and forestry pests. It also serves as a vector for
Paederus dermatitis, which is prevalent in most tropical and subtropical countries worldwide.
Paederus dermatitis, also known as linear dermatitis, is a skin condition caused by the rupture of nymph bodies. When their body fluids come into contact with human skin, they can cause acute erythematous vesicular lesions [
1,
2]. This insect has a wide distribution and is found across the globe outside of Antarctica, demonstrating strong invasive and environmental adaptation capabilities [
3,
4]. It inhabits moist environments such as riverbanks, swamps, and irrigated fields [
5]. The generation number of
P. fuscipes is related to temperature, humidity, and food availability. In regions like Jiangsu, Guangxi, and Anhui in China, three generations occur. They overwinter as adults, but in some areas, their overwintering is not during the winter; rather, their activity and population fluctuations seem to be caused by low humidity in the dry season [
1,
6]. They have a wide habitat range, often feeding on agricultural pests. Therefore, larvae and pupae of other insects become prey for rove beetles [
7].
P. fuscipes can prey on various agricultural pests, such as aphids, leafhoppers, and planthoppers, and thrip on crops like rice, wheat, cotton, corn, and legumes, playing a significant role in biological pest control [
8].
Species distribution models (SDMs) are empirical methods used to quantify the ecological niche of a species in its environment. By combining occurrence data samples of the target species with environmental variables from sample locations, SDMs infer the relationship between species and environment, thereby predicting the potential distribution of the species [
9,
10,
11]. Commonly used niche models include CLIMEX, BIOCLIM, GARP, DOMAIN, and MaxEnt [
12]. Among these models, the MaxEnt model is widely applied in various fields due to its advantages of using small sample sizes for prediction, high accuracy, fast computation speed, and simple operation [
13,
14]. Spatial data modeling has become an increasingly important tool and is widely used in ecology, conservation, evolutionary biology, geography, and climate change research [
15,
16]. Its applications include assessing the potential impact of climate on species [
17,
18], predicting the potential distribution of endangered plants [
19], evaluating invasive species [
20,
21], and identifying and assessing flood indices and risks in urban areas [
22], among others.
Currently, there is relatively little research on
P. fuscipes in China. Existing studies mainly focus on its biological characteristics [
6], chemical composition [
7], predatory behavior [
23], and the inhibitory mechanisms of plant essential oils on
P. fuscipes [
24]. There is limited research on the potential suitable habitats for
P. fuscipes.
This study analyzed the environmental suitability of P. fuscipes based on known distribution data and Chinese environmental data, using the MaxEnt model and ArcGIS technology. We predicted the current and future potential distribution of P. fuscipes and analyzed the trend of centroid shift in its potential geographic distribution, providing a theoretical basis for pest control.
4. Discussion
This study utilized the MaxEnt model in conjunction with distribution data of
P. fuscipes and key environmental variables to analyze its current suitable distribution locations in China [
35]. Additionally, it also examined changes in suitability distribution under different future climate scenarios and explored the relationship between these changes and environmental variables. The model evaluation results indicated an AUC value of 0.968, suggesting a high level of accuracy in the model.
The prediction results of the MaxEnt model indicate that
P. fuscipes has four distinct habitat suitability zones: high suitability, moderate suitability, low suitability, and unsuitable zones. The current distribution of suitable zones is relatively concentrated, with notably suitable zones in Xinjiang and Tibet. The high suitability zones are mainly concentrated south of the Sichuan Basin, north of the Yungui Plateau, in the southeast hills, the middle and lower reaches of the Yangtze River Plain, Hainan Province, and the northeastern direction of Taiwan Province, primarily focusing on the southern regions of China. Under future climate scenarios, the area of high suitability zones decreases significantly, and there is a trend of expansion and extension towards the coastal areas for suitable zones.
P. fuscipes primarily inhabits humid environments such as riverbanks, marshes, and irrigated fields, which aligns with previous research findings [
5]. Hunan is currently the province with the largest high suitability zone area in China, but under future climate scenarios, the high suitability zone area decreases while the areas of moderate and low suitability increase. Compared to North China, the northeast, and the northwest regions, East China and Central South China have the largest areas of high suitability. East China is located in the eastern part of China, characterized by hills, basins, and plains, with a subtropical monsoon climate a temperate monsoon climate, and abundant water resources. The climate conditions in Central and South China are similar to those in East China, mainly consisting of subtropical monsoons, temperate monsoons, and tropical monsoons. Annual rainfall ranges from 400 to 3000 mm, with annual accumulated temperatures exceeding 3000 °C. They are characterized by hot and rainy summers, humid and hot conditions, mild and wet winters, and distinct seasons. Analyzing
Figure 4 and
Table 4, over time, both the high and low suitability areas of
P. fuscipes show a decreasing trend, with the most suitable habitats expanding towards the southeast. However, the high suitability areas are mainly concentrated in Shandong, Jiangxi, Anhui, Hubei, Henan, and Hebei provinces. With global climate warming, areas that were once suitable for
P. fuscipes have become low suitability or unsuitable areas, while some unsuitable areas have become suitable habitats. In addition to climate factors affecting this insect, the distribution of various crops may also have an impact. Zhu et al., (1984) [
8] pointed out that the distribution and occurrence of
P. fuscipes in fields are closely related to the occurrence of pests in different crop types.
P. fuscipes shifts with the occurrence time and quantity of various crop pests, which may be a reason for its future spread toward the southeast.
Temperature, precipitation, altitude, and other environmental variables have direct and indirect impacts on insect survival [
36,
37]. Temperature is an important environmental and survival factor for insects, including
P. fuscipes. Insects are ectothermic animals, meaning their body temperature changes with environmental temperature fluctuations. These changes in body temperature can directly accelerate or inhibit metabolic processes, affecting their growth and reproduction [
38]. This study used jackknife tests combined with Pearson correlation coefficients to select the important environmental variables that limit the distribution of
P. fuscipes, which we identified as follows: bio11, bio9, bio14, bio7, bio6, bio2, bio3, bio13, and bio15. The results indicate that temperature and precipitation are significant factors affecting the distribution of
P. fuscipes. The optimal temperature for the mean temperature of the coldest quarter is 6.06 °C; for the minimum temperature of the coldest month, it is −1.84 °C; for the mean temperature of the driest quarter, it ranges from 3.37 °C to 41.30 °C; and the optimal precipitation for the driest month is 42.89 mm. The suitability value curves for several major environmental variables show steep rises and falls, with narrow suitability value ranges. This may be one of the reasons why the suitability area of
P. fuscipes is significantly reduced in future predictions [
39,
40]. Humidity, solar radiation, and air temperature affect the metabolic rates of animals and plants in tropical forests [
41]. Previous studies have also shown that
P. fuscipes prefers to overwinter in crop fields with dense vegetation cover that is relatively sheltered from the wind and cold. However, the humidity levels vary, with some areas being very humid and others even somewhat dry [
8,
42]. This also explains why
P. fuscipes may appear in areas where it was previously unsuitable for growth in the future.
In addition to analyzing the current distribution, future distributions of P. fuscipes were also predicted. Under three typical greenhouse gas concentration scenarios, SSP1-2.6, SSP2-4.5, and SSP5-8.5, the area of highly suitable habitats for P. fuscipes in the 2050s (2041–2060) and 2090s (2081–2100) significantly decreased. Only a small amount of highly suitable area remained in a few areas such as Guangxi, Hunan, Fujian, Guangdong, and Guizhou, with the most pronounced decrease observed in the 2090s under the SSP1-2.6 scenario, with a reduction rate as high as 98.16%. Comparing greenhouse gas concentrations, the reduction in suitability was significantly greater under SSP1-2.6 than under SSP2-4.5 and SSP5-8.5, indicating that P. fuscipes’ suitability is poorest under low greenhouse gas concentration environments. The areas of high suitability and low suitability are decreasing to varying degrees, while the area of moderate suitability is increasing to varying degrees. However, considering all scenarios for high, moderate, and low suitability areas, both the 2050s and 2090s show a significant reduction in suitable habitats, indicating a weakening trend in the future suitability of P. fuscipes. The expansion of suitable habitats is moving towards regions such as Xinjiang, Gansu, Liaoning, and Inner Mongolia, mainly located in the northwest, north, and northeast regions of China with a temperate continental climate characterized by cold winters and hot summers and significant annual and daily temperature variations. This may be related to climate warming caused by high CO2 emissions in the SSP5-8.5 scenario. Climate warming is causing temperatures to rise in traditionally cold regions like Inner Mongolia and Xinjiang, allowing P. fuscipes to expand into new territories. The current centroid of this insect is at 105°93′ E, 30°52′ N, but in the future, under different gas concentration scenarios, the centroid is projected to shift slightly southeastward from the 2050s to the 2090s, indicating no major directional shift in the suitability area of P. fuscipes.
Ecological indicators only describe the basic ecological requirements of a species and do not represent its actual ecological needs. When using species distribution models to predict potential distributions, various biotic and abiotic factors that influence species distribution are often overlooked [
43,
44,
45]. The MaxEnt model used in this study is based on known distribution data for the target species and selected environmental data to study the species’ distribution probability. Although it has good predictive results, the selected environmental variables are limited, with only temperature and precipitation being considered, while other environmental factors are not included in the model. While the MaxEnt model has universal advantages in predicting potential species distributions, it also has limitations [
27]. Response curves only show the impact of a single environmental factor, ignoring interactions between variables. Considering all environmental factors comprehensively in a specific model analysis is impractical, so treating this model as a fundamental niche model may be more effective [
46]. As an insect,
P. fuscipes’ survival factors are influenced not only by its biological characteristics but also by crop distribution, predators, human activities, and other environmental factors [
47,
48]. Future studies on the suitable habitat of
P. fuscipes, including both biotic and abiotic factors such as human activities and host types in the model, can improve the accuracy of model predictions.
5. Conclusions
Based on known distribution information and climate factors of P. fuscipes, MaxEnt modeling, and ArcGIS technology were successfully used to predict the current and future suitable habitat distribution of P. fuscipes in China. The results indicate that the main environmental variables influencing its distribution are bio11, bio9, bio14, bio7, bio6, bio2, bio3, bio13, and bio15. Under the current climate conditions, high suitability areas are mainly distributed south of the Sichuan Basin, north of the Yunnan-Guizhou Plateau, in the southeast hills, the middle and lower reaches of the Yangtze River Plain, Hainan Province, and the northeastern direction of Taiwan Province. In the 2050s and 2090s, under three typical greenhouse gas concentration scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5), high suitability habitat areas for P. fuscipes significantly decreased. The decrease is most significant under the SSP1-2.6 low-concentration greenhouse gas scenario, and the predicted centroid position of potentially suitable habitat areas tends to move southeastward. This study provides a new perspective on the distribution and environmental impact factors of P. fuscipes, promotes its use as a biological control agent against other pests, and provides necessary references for its application in agricultural and forestry pest control.