Evaluation on color preference of adult mulberry psyllid (Paurocephala sauteri Enderlein)

Abstract:【Objective】Paurocephala sauteri has become an invasive pest of mulberry in mainland China in recent years. It mainly damages terminal bud and tender leaf of mulberry and causes high poten- tial losses (40%) in leaf yield and quality. The adults and all the nymphs could secrete wax and lead to the occurrence of sooty mold. As a kind of small pest mainly growing in tropical and subtropical area, it has higher reproduction rate, and one generation takes only about 18 days at 28 °C. Together with the generations overlapping as well as the increasing resistance to insecticide, it is very difficult to control. Trapping technology based on chromatic cues is an important strategy in controlling the pest of Hemip- tera. Chromatic cue has been used in the manufacture of various colored sticky cards for trapping pests. The trapping effect and the operability could be severely affected if the most effective wave length is not selected properly. Up to now, no color preference of P. sauteri has been investigated. Base on ten different color sticky traps, the objectives of present study were to evaluate the preference of P. sauterito different chromatic cues, in that the RGB values were quantitatively converted into virtual wave- lengths, which provided a feasible method to set optimal color parameters for trapping P. sauteri. In addition, the effect for trapping natural enemy insects, and the trap height as well as the hanging position for P. sauteri attraction were studied, so that an easy and precise prevention and control method could be explored.【Methods】Ten types of different colored sticky card traps (red, yellow, green, blue, black, gray, cyan, violet, pink and white) were evaluated for the color preference of P. sauteri in the field. Then the optimum color was screened after RGB values and virtual wavelengths (565，570，575, 580，585，590 and 595 nm) were converted for each other based on Dan Bruton’s wavelength to RGB function. Seven different wavelengths of color papers were printed by a color printer based on RGB values to test the color preference of female and male P. sauteri adults after their emergence of 1 d and 3 d in a laboratory in an octagon maze. Then the preference of P. sauteri to the seven wavelengths at different hanging height (20 cm, 10 cm lower than the top of the mulberry trees, 0 cm, 10 cm, 20 cm and 30 cm above the top of the mulberry tree) and position (hanging with its longer sides parallel or perpendicular to the plant rows) were also evaluated in the field.【Results】The screening results of ten different color sticky traps showed that yellow color was the optimum color for trapping P. sauteri adults. The laborato- ry study on the preference of P. sauteri adults to seven different wavelength color papers showed thatP. sauteri adults of 3 d old were more selective to different colors than the individuals of 1d old, and they were prefer to the color papers with the wavelengths of 570 nm and 595 nm, which could also attracted more male individuals than female ones. The attractiveness difference among the seven colors to 1d old adult individuals showed that, there were some differences among females, but no attractiveness difference was observed among male individuals. The preference of the color paper with the spectrum of 580 nm showed the lowest attractive rate to the female and male adults of 3 d old and females of 1 d old. The trapping results in the field showed that the orders of P. sauteri preference to the seven wavelengths of color papers were as follows: 595 nm>570 nm>590 nm>565 nm>575 nm>580 nm>585 nm. Further trapping investigation found that the color papers with the spectrum of 595 nm showed the lower at- tractive rate to natural enemy insects than those with 570 nm. The trap height and hanging position also significantly influenced P. sauteri attraction efficiency. It was found that the lower edge of the colored traps hanging on a height of 0 cm or 20 cm above the top of the mulberry tree was the optimum height for trapping P. sauteri, and that the individual numbers of P. sauteri on colored traps hanging parallel to plant rows was significantly higher than those on traps hanging perpendicular to plant rows.【Conclusion】In conclusion, the color traps with the spectrum of 595 nm installed at 0 cm or 20 cm above the top of the mulberry tree as well as hanging on parallel with the line of mulberry tree showed the maximum effect for trapping P. sauteri and the lowest effect for trapping natural enemy insects. It provided a useful basis for the proper control of P. sauteri by using their visual cues. These parameters can be applied to produce paper trap cards, plastic trap plates and plastic bottles combined with lure odors.