Biological control of aphids in maize, wheat and alfalfa in the landscapes of Ili, China

Introduction

Part of the pests in farmland are controlled by natural enemies, and the other part are controlled by the artificial spraying of pesticides. When the population density of natural enemies in the environment decreases, farmers often have to use more pesticides as a substitute, which brings about more environmental pollution and food safety problems. When the use of pesticides increases, natural enemies are exposed to a more toxic environment, and their population continues to decline. Meanwhile, pests get rid of the control of natural enemies and gradually develop resistance to pesticides, making pest outbreaks in farmland more likely. As a result, more pesticides are needed for pest control, creating a vicious cycle. Therefore, increasing the proportion of pest control by natural enemies in the overall pest control in farmland is conducive to the sustainability of pest control.

Natural enemies move and disperse within the agricultural area by flying and crawling. Therefore, natural enemies in farmland can originate from any space within a certain range around the farmland. The population density of natural enemies in farmland will be affected by the land use situation (i.e., the landscape) within a certain range (such as within a diameter of 4 kilometers). Previous studies have shown that the responses of the population densities of natural enemies in different crop fields to the surrounding landscape may be completely different. When different crops are planted within the same landscape, these crops will simultaneously recruit natural enemies from the landscape. So far, it is still unknown which factors will affect the ability of crops to recruit natural enemies.

Project description

The Ili River Valley is in the western part of the Tianshan Mountains, Xinjiang, China. It opens westward with a flat terrain, while the other three sides are surrounded by Tianshan Mountains. The unique geological feature equips the Ili River Valley with diversified natural habitat types in agroecosystems, for example, desert steppes (the ecotone between desert or and oasis, or arid leeward mountain slopes), river belts, mountain meadows, weed strips, forestry, and more abundant water resources than other regions of Xinjiang blocked by mountains (Li et al., 2023; Min et al., 2021). These factors contribute to the highest level of biodiversity of vegetations and predators in this region, endowing the Ili River Valley with the greatest potential for achieving success in CBC within the desert-oasis agroecosystems of Xinjiang (Aerziguli et al., 2020; Li et al., 2011).

Of all the crops that cultivated in Ili, corn (≈35%) and winter wheat (≈25%) are the most dominant crops cultivated (Statistics Bureau of Xinjiang Uygur Autonomous Region, 2022). These two types of crops are often directly adjacent to each other in the local area, forming a combination of 2 crop species that cropped under the same landscape pattern. These two types of crops are infested by the same kinds of pests (for example, aphids, cotton bollworms) and recruit almost the same natural enemies (for instance, Hippodamia variegata, Orius spp., larvae of hoverflies, et al.) in the landscape for pest control. However, there are significant differences in their phenology. Winter wheat is infected by pests in early June. It recovers early in spring but becomes the reservoir in June (Ronghua Lin et al., 2003). After it is harvested, natural enemies it harbored will transfer to other croplands, for instance corn, and provide biocontrol services (R Lin et al., 2003; Ouyang et al., 2020). In this project, we will investigate the effects of landscape composition on the abundance and diversity of natural enemy in corn and winter wheat; access whether the landscape effects are same between winter wheat and corn; and analysis which factors determine the attractiveness of different crops in recruitment of natural enemy.