Biological monitoring is an essential condition for characterizing species diversity (van der Heyde et al., 2020, Vivien et al., 2015), assessing the ecological status of ecosystems (Andreasen et al., 2001, Vivien et al., 2015), and detecting the presence of invasive or pest species (Guareschi et al., 2020, Hardulak et al., 2020). As one of the most crucial terrestrial ecosystems on the planet, agricultural ecosystems have long been the most important resources for people to meet food, fiber and fuel needs (Swinton et al., 2007). Species diversity is a critical factor for the stability and sustainable development of agroecosystems (Ratnadass et al., 2011), thereby the biodiversity monitoring for agroecosystems is a long-term task in ecology-related fields. In agroecosystems, animals widely exist on nearly all continents as the largest quantities group of macroscopic organisms, functioning as biocontrol agents, pollinators and prey (Giribet & Edgecombe, 2012), playing a central role in the study of speciation, community ecology, biogeography and climate change (Pollard & Yates, 1994). Traditional animal community monitoring has largely been done with visual surveys or by passive sampling capturing specimens to identify and count species (Ji et al., 2022). Monitoring efforts requires researchers possessing rich knowledge on taxonomy and conducting careful analysis of morphological characteristics of specimens (Packer et al., 2009). However, these traditional survey methods are increasingly unable to meet the needs of large-scale diversity surveys. The reason is that different trapping methods often capture only a subset of actual biodiversity (Svenningsen et al., 2021, Krehenwinkel et al., 2022a) and large amounts of specimens (e.g., specimens of bees) could also make a biomonitoring extremely time-consuming (Gueuning et al., 2019).
As an important element of biomonitoring, environmental DNA (eDNA) is revolutionizing the way researchers monitor the biome inferring species presence and absence indirectly through molecular approaches (Coissac et al., 2012, Deiner et al., 2017, Valentini et al., 2016, Veilleux et al., 2021), whose surveys do not rely on visual observations, thereby simplifying species detection within inaccessible environments (Fediajevaite et al., 2021) and could identify simultaneously the large sets of taxa present in a bulk environmental sample (Taberlet et al., 2012b). To date, it has been turned out to be a reliable, reproducible, and time-effective tool in species discovery of the environmental samples from soil, scats (faeces), plant material, water, or air (Deiner et al., 2017, Taberlet et al., 2012a), which has been recommended as the primary approach for large-scale biomonitoring in plant species diversity of biodiversity coldspots (Liu et al., 2023), soil arthropod communities (Oliverio et al., 2018, Ustinova et al., 2021), fish diversity across river-lake connected system (He et al., 2022, Zhang et al., 2022), plants-pollinators interactions (Bell et al., 2022), and planktonic and benthic diatoms communities (Wang et al., 2019, Zhang et al., 2023). However, in agriculture, such superior technology is not widely used for plant-animal associations biomonitoring (Kestel et al., 2022), especially for that of the economic crops.
Cowpea (Vigna unguiculata (L.) Walp.) is an annual herbaceous plant belonging to the genus Vigna of the family Fabaceae (Wu & Mats, 2010), which widely distributed in Africa, Asia and Latin America (Ehlers & Hall, 1997). Cowpea is rich in nutrients, including vitamins, minerals (Ca, P, Fe), folate, thiamin and riboflavin, is a very important food source supplementing carbohydrates and proteins for people in developing countries (Mucheroa et al., 2009, Behura et al., 2015). In China, cowpea is widely cultivated over the country with planting area more than 0.67 million hectares and annual production for about 1.5 million tons, is an economically important crop in Fujian, Guangdong, Guangxi, Hainan, and Yunnan province where tropical or subtropical climate (Huan et al., 2015, Huan et al., 2016). However, cowpea in China is often infested and damaged by many insects during growth, especially in Hainan province with a warm and wet tropical climate (Huan et al., 2016, Wu et al., 2023). Moreover, with the indiscriminate use of pesticides, some small insects occurred are becoming more serious in recent years in Hainan region (Wu et al., 2023, Guo et al., 2023). Accurate species monitoring is a fundamental condition for precise pesticide application, which could avoid damage to some beneficial species (e.g. natural enemy) (Schmidt-Jeffris, 2023). Previous studies showed that Megalurothrips usitatus (Thysanoptera), Maruca testulalis (Lepidoptera), Liriomyza sativae (Diptera), and Aphis craccivora (Hemiptera) are main insects associated with cowpea occurred seriously in Hainan region (Li et al., 2022, Wu et al., 2023). However, these studies only focused on the pests, for other related species, how many kinds of that is unknown. Furthermore, we observed that there were at least nine species of insects potentially associated with cowpeas during our sample collection (Fig. 1). In view of this, we have reason to believe that the species related to cowpeas may be a large community which most of it has yet to be revealed on account of the limitation of monitoring way. Hence, it is necessary adopting a powerful approach to strengthen the monitoring of animal diversity associated with cowpeas and to accurately assess changes in biodiversity.
Here, we focus on the planting areas of cowpea in Hainan province, then collect cowpea flowers gaining eDNA for animal community monitoring using DNA metabarcoding. This study aims to address the following questions: (i) how many other species are associated with cowpeas except for the major known pests? (ii) if species richness, whether there are differences in species composition between different planting regions. The present study would broaden the horizon of species diversity for cowpea associated animal communities and provide basic information for further application of precise pesticide in cowpea.