## 2 Materials and Methods
### Experiment Design
#### 2.2.2 Spray-Deposition Measurements  
The experiment consists of five treatments: four kinds of spray equipment treatment and a blank control. The spray deposition, the control efficacy on wheat aphids and working efficiency were tested. The spray deposition and the control efficacy were tested in a 170 m \(\times\) 190 m area (Figure 3A). In the test field, treatments were arranged within the location as a randomized complete block design with three replications, resulting in three blocks each with five plots corresponding to different treatments. Each plot was a 30 m \(\times\) 50 m area. Ten-meter buffer zones [17,19] between plots were set to avoid the drift pollution (Figure 3A). Figure 2: The test location and the brief overview of the studied wheat field. The experimental fields are marked with red flags. Prior to the application in each treatment, sample collectors were placed at each plot in five equally-spaced sample sites. Each sample site was 5 m apart and spanned a total of 20 m. The sample sites were repeated three times with an interval of 15 m between each repetition. To avoid cross contamination between plots, sampling was arranged at the center of the plots, as shown in Figure 3A. Sample collectors at each sample site consisted of one water-sensitive paper (WSP) (25 mm \(\times\) 75 mm) and four filter papers (90 mm in diameter) (Figure 3B). The WSP was used to evaluate the characteristic of deposition such as an area of coverage, number of spray deposits and droplet size. The filter papers were used to measure the deposition distribution in the canopy. The WSPs were fixed horizontally on plastic rods through double-headed clamps. The heights of these clamps were adjusted to assist in positioning at a height equivalent to the head of the wheat canopy. The filter papers were used to simulate leaves to collect foliar deposition at different heights and losses to the ground. On each sampling site, three filter papers were attached on the wheat head, flag leaf and third top leaf of one wheat plant. To evaluate the losses to ground, a filter paper was placed on the ground. In all tests, 70% Imidacloprid-Regent Water dispersible granule (WDG) at 85.7 g a.i./ha (active ingredient) (Zhejiang Sega Science and Technology Co., Ltd.) and allure red (80% purity, purchased from Beijing Oriental Care Trading Ltd.) were added into the tank. The pesticides were prepared according to the recommended dose. Allure red was used as the tracer according to the spraying area at 450 g/ha. Allure red, a water-soluble colorant, is frequently used in these types of studies [3,9,15]. It presents high recovery rate, high photostability and low acute toxicity in different species of animals according to the Joint FAO/WHO Expert Committee on Food Additives as well as the European Union's Scientific Committee for Food. Nearly 30 s after spraying, five randomly selected wheat plants of over ground part, WSPs and filter papers of different canopy positions at each sampling site were collected and placed in labeled plastic zip-lock bags. Five random wheat plants were combined and bagged as one sample. The sample of wheat plants was used to measure the total deposition per plant. For each plot, there were 15 wheat plant samples, 60 filter papers (4 from each sampling site) and 15 WSPs. All samples were placed  
Figure 3: **(A)** Experimental layout of each treatment; and **(B)** placement of filter papers and water-sensitive paper at each sampling position within the wheat canopy. in zip-lock bags along with a label describing the treatment, replication, and location information. Samples were placed into light-proof seal box immediately after collection and transported to the laboratory for analysis. Each filter paper and the wheat sample were washed in 0.02 L and 0.2 L of distilled water in the collection bags, respectively. Samples were agitated and vibrated for 10 min to allow the dye to dissolve into the water solution. Previous tests have shown that this methodology results in near total recovery of dye deposited on samples [22].