## 3 Results and Discussion  
### Control Effect against Thrips on Cowpea  
Cowpea is one of the main economic crops in Hainan Province. Thrips are one of the main pests that endanger the yield and quality of cowpea. The unique climatic environment has created favorable conditions for the reproduction of thrips and caused huge losses to farmers' income. Pesticide application has become the most commonly used method to control cowpea thrips. With the increasing awareness of food safety, pesticides with high efficiency and low risk have received more and more attention. Biopesticides have become a hot spot in current research and development and application. Spinetoram, a new spinosyn insecticide that is more effective than the related pesticide of spinosad but maintains spinosad's low toxicity to mammals and other non-target species, is currently widely used to control lepidopteran larvae, thrips, leaf miners, etc. [41]. In the present study, spinetoram was selected to perform the field control against thrips on cowpea. The pesticide application equipment greatly affects the pest control effect and labor cost. For local farmers in Hainan Province, the commonly used spray equipment for cowpea pest control is knapsack electric and stretcher-mounted power sprayers. With the increase in land intensification and the shortage of rural labor, plant protection UAVs with multiple advantages and suitability for a variety of terrains are moving towards the center of the stage. Nevertheless, people are always considering whether plant protection UAVs can achieve the same or better control effect as ground-based, high-efficiency pesticide application equipment. In this work, the comparison of field control effect against cowpea thrips between UAVs and knapsack electric sprayers was conducted. In order to clearly demonstrate the difference of control efficiency, all the treatments applied the same dosage of active ingredient per hectare (300 mL of 60 g/L spinetoram SC/ha). Following the treatments, the control effect was observed and calculated on the first, third, and fifth day. The field control effects (%) against cowpea thrips sprayed by  
Figure 2: Coverall sectioning for whole-body dosimetry analysis. 1: head, 2: left arm, 3: right arm, 4: chest, 5: back, 6: right thigh, 7: left thigh, 8: left leg, 9: right leg. UAVs and knapsack electric sprayers are presented in Table 2 and Figure 3. When using a knapsack electric sprayer to control cowpea thrips, the control effects on thrips on the first, third, and fifth day were 68.55%, 67.98%, and 65.23%, respectively. All of these values were lower than those treated by UAV sprayers on the same day, indicating the enhanced field control effect by UAV application. For UAV spraying, when the amounts of water applied per hectare were 22.5, 30, and 37.5 L, the control effects on thrips on the first day were about 69.79%, 80.15%, and 80.58%, respectively. On the fifth day, those values were found to be 69.73%, 75.61%, and 73.68%, respectively. The results demonstrated that the control effect could be enhanced by increasing the amount of water from 22.5 to 37.5 L per hectare, which could most likely be attributed to the improved spraying coverage and droplet density on the target cowpea. However, when the volume of water increased from 30 to 37.5 L per hectare, there was little difference in the control effect on thrips at the same time. Considering the operating efficiency and cost of the UAV, the best liquid consumption to control cowpea thrips was 30 L per hectare under the experimental conditions. Compared to the huge water consumption of 600 L per hectare for knapsack electric sprayer, UAV treatment can not only improve the effectiveness of prevention but also greatly reduce water consumption and working time, which is the direction for the development of green and high-quality agriculture.