Study on the preference of Diaphorina citri Kuwayama to different colors

Abstract：【Objective】Citrus is an important economic crop in China, and Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is a serious pest of citrus. It is also an important medium for spreading Huanglongbing the most devastating diseases on citrus production. In general, the areas where the Huanglongbing occur are also the distribution areas of D. citri. Currently, the control of D. citri relies largely on chemical insecticides. Intensive chemical control can induce many side effects, such as toxicity to non-target organisms including human beings, development of insecticide resistance, and insecticide residues on agricultural products and in the environment. To minimize such effects, alternative control strategies are required. One of the alternatives is to use color sticky traps. This method can be used in population monitoring, which can reduce the population density of pest. The purpose of the present study is to investigate the preference of D. citri to different colors.【Methods】In this study, the evaluated colors on the basis of the RGB color mode were set as red (255, 0, 0) , orange (255, 128, 0) , yellow (255, 255, 0) , chartreuse (128, 255, 0) , lime (0, 255, 0) , cyan (0, 255, 255) and blue (0, 0, 255) . The selfmade cuboid and octahedral devices were used to study the preference of D. citri to different colors.The indoor monochrome selection test of D. citri was tested with the cuboid device. The test was conducted in an indoor dark room at a temperature of (27.0 ± 2.0) ℃ and a relative humidity of 60.0%-70.0%. Illumination was provided by hanging a white fluorescent light (20 W) , 0.5 m above the cuboid device. The papers of the tested colors and the white (control) were stuck on the ends, respectively. For each bioassay, D. citri was individually introduced into the cuboid device from the middle part. The insect that felled on one of the tested paper was recorded after it remained for staying at least 60 s. Afterfive insects had been tested, the cuboid device was rotated 180° to randomize any positional effects. Sixty female and male D. citri adults were tested for each color, and each insect was used only once. In addition, the indoor multi-color selection test of D. citri was tested with the octahedral device. For each bioassay, thirty female and male D. citri adults were introduced into the octahedral device for 50 replicates respectively. After 10 min, the numbers of the insects that felled on each color paper were recorded. The indoor conditions and operation of the octahedral devices were described as above for those of the indoor monochrome selection test.【Results】There were significant differences in the preference of the female and male adults to seven colors. Yellow color exhibited the strongest attraction to D. citri and followed by chartreuse. In the indoor monochrome selection test, females and males of D. citri were sensitive to the colors. Females and males were significantly attracted to yellow (female: c2=32.267, p < 0.01; male: c2=15.000, p < 0.01) , chartreuse (female: c2=11.267, p < 0.01; male: c2=4.267, p < 0.05) , and lime (female: c2=9.600, p < 0.01; male: c2=8.067, p < 0.01) . However, red color showed a significantly weak attraction to D. citri females (c2=5.400, p < 0.05) and males (c2=17.067, p < 0.01) . In the indoor multi-color selection test, there were also significant differences in the selective rate of adult D. citri females and males to seven colors. Females and males were also significantly attracted to yellow and chartreuse, followed by orange color. The sequence of their selection response rates to the seven colors were: yellow ≥ chartreuse > orange > white > lime > red > cyan > blue. Red, cyan and blue colors exhibited the significantly negative attraction to D. citri females and males. According to the Dan Bruton's color-to-wavelength conversion relationship, the relationship between the selection rate and the virtual wavelength of D. citri was analyzed. The preference of D.citri was mainly concentrated at 510-617 nm, and the male and female adults had a consistent selection trend to the virtual wavelength with the highest point between 540-580 nm.【Conclusion】Diaphorina citri was sensitive to the colors, especially the yellow (580 nm) and chartreuse (540 nm) . In the integrated pest management (IPM) programs, yellow and chartreuse can be exploited as the color of sticky traps to monitor and manage the population of D. citri. The RGB color model was used to study the visual preference of D. citri, which provided a new idea for the accurate screening of effective color-sticky traps against D. citri. The research on the preference of D. citri is mainly carried out in the indoor environment. Under the outdoor natural conditions, the selection of D. citri may be interfered by the host, illumination and climatic conditions. Therefore, the results need to be further verified in the field.