## 1 Introduction  
Pesticides are an important material basis for ensuring food security as well as world peace and stability [1, 2]. Estimated by FAO, the use of pesticides can restore the loss of 30-40% of the world's total crop production. Humankind's rigid demand for pesticides will exist for a long time. However, agricultural pesticide handlers are often exposed to high levels of pesticides due to missing or improper personal protective equipment (PPE), leading to potential adverse health impacts on these agricultural workers [3]. These exposures occur mainly through inhalation and dermal contact with pesticides when mixing, loading, cleaning equipment, applying the spray mixtures, or entering sprayed areas [4]. Generally, pesticide contamination during spraying makes the greatest contribution to occupational exposure, which is scenario dependent. Multiple factors affect the amount of exposure, such as the application equipment, type of pesticide formulations, crop height and canopy density, application rate and duration, climatic conditions, PPE, and the training and aptitude of the applicators [5]. In tropical regions or countries, pesticide applicators are more vulnerable to dermal exposure than their counterparts in temperate countries [6]. This is ascribed to the fact that operators there do not usually wear PPE during pesticide application activities, mainly due to the discomfort associated with the use of PPE under humid and salurry weather conditions [7]. Hainan Province is located in a tropical region and has a climate and ecological advantage of being one of the major winter melon and vegetable production bases in China. However, due to suitable environmental conditions, insect pests and plant diseases are prone to occur all year round, resulting in a tremendous amount of pesticide consumption [8]. As a result, frequent pesticide application and humid climatic conditions bring about great exposure risk to pesticide applicators. Cowpea, _Vigna unguiculata_ L. [PERSON], is an important grain legume in the tropics and one of the major winter vegetables in Hainan Province [9]. Insect pests and diseases of cowpea have inflicted a severe impact on cowpea yield and quality [10]. In order to avoid great economic losses, farmers have resorted to indiscriminate use of pesticides to reduce the damage. The commonly used local spray equipment for cowpea pest control is stretcher-mounted power sprayers and knapsack electric sprayers. The local farmers always put themselves in a \"spray cloud\" when performing the spraying using this equipment (Video S1). Due to the higher cowpea height and density, the spraying of the pesticide solution with these sprayers will bring about great exposure risk to the applicators. Thus, it is highly desirable to develop new spraying equipment to minimize the pesticide exposure level without sacrificing the control efficiency of insect pests. Due to their flexibility, high efficiency, and lower labor intensity, unmanned aerial vehicles (UAVs), also called drones or unmanned aerial systems (UASs), have attracted considerable attention in precision pest management [11]. Without the need for specific take-off and landing sites, rotary-wing UAVs can operate flexibly and efficiently in complex and uneven terrain, such as paddy fields, hills, and mountains, and they respond quickly to the outbreak of pests [12]. The recent fast development of real-time, high-precision kinematic positioning, flight control, obstacle avoidance, and terrain-following technologies boost the massive application of UAVs in the plant protection field [13]. In China, the academic research and practical applications of UAVs are developing rapidly [14]. According to the statistics data by the Chinese agricultural department, nearly 100,000 crop protection UAVs are used in China, and the spraying area reached about 66 million hectares in 2020.