Study On Phototaxis Of Pissodes Punctatus And Its Three Main Parasitic Wasps

Long-term using of chemical pesticide in pest control has caused great damage to environment, human health and biodiversity. Developing of substitute technology eco-friendly is necessary for pest control. Light trapping and color trapping is an effective physical pest control which take use of phototaxis of pest, and has been popularized and applied in large-scale pest control. At present, most studies and applications on the phototaxis of pest were focused on main pests in agriculture. Pissodes punctatus Langor et Zhang is a destructive stem borer to Pinus armandi Franch and is difficult for control and monitor. Few papers reported whether color and light trapping do harm to natural enemy of pest or not. This study examined the phototactic behavior of P. punctatus through observation of its phototactic response to nine monochromatic lights ranging from340nm to689nm with about40-nm step and response to five light intensities in the door. The phototactic behavior of P. punctatus was also tested using color and light trapping at different intervals, directions and heights in the field. Furthermore, this paper studied the phototaxis characteristics of three main parasitic wasps for P. punctatus, including Scleroderma guani Xiao et Wu, Dinotiscus armandi Yang and Triaspis sp. At last, the paper compared the difference in the sensitive monochromatic light and light intensity between P. punctatus and its three parasitic wasps. These results could provide a reference for light traping of P. punctatus and could protect natural enemies of the weevil better. These results could also provide a reference for population monitor to P. punctatus and its three main parasitic wasps. The results are as follows.1Phototactic characteristics of P. punctatusP. punctatus was attracted to all nine monochromatic lights, which implied its broad sensitivity to the spectrum of light. P. punctatus was most sensitive to wavelength415nm violet,340nm ultraviolet, and504nm green lights, suggesting there might be at least three types of photoreceptors in the compound eyes of this weevil. Contrasted with darkness or natural light, the phototactic responses of P. punctatus to orange, blue, and green lights were ordered in different sensitive sequence. Furthermore, low intensities elicited an increased phototactic response, and high intensities a decreased phototactic response, under violet, UV light and green light which suggested the phototaxis behavior of P. punctatus is intensity preference. Under three most sensitive monochromatic lights, relative light intensity caused the maximum of phototactic response of P. punctatus in the following order: UV, violet and green light.2Field trapping of of P. punctatusIn five colors of light trapping, the quantity of trapped P. punctatus reached the maximum in the following order: violet, green, yellow, blue and red light. The quantity of trapped weevils by violet light is significantly more than those trapped by trapping lights of other colors. In six colors of color trapping, the quantity of trapped P. punctatus reached the maximum in the following order: violet, yellow-green, green, yellow, blue and red light. The quantity of trapped weevils by violet color is significantly more than those trapped by other colors. The result of color trapping is more consistent with its phototactic response under natural light than that under darkness. There was no significant difference in quantity of trapped weevils among three heights of violet color trapping, including1.5m,3.0m and4.5m. Violet color trapped more P. punctatus during early-afternoon (12:00-15:00) than that during early-morning (0600-0900), late-morning (0900-1200) and late afternoon (15:00-18:00). P. punctatus was trapped more at southwards than that at eastwards, westards and northwards. Thus, P. punctatus can be trapped easily by violet color trapping at1.5m height at southwards all day.3Phototactic characteristics of Scleroderma guaniS. guani was attracted to eight of nine monochromatic lights except wavelength689nm red light, which implied its broad sensitivity to the spectrum of light. S. guani was most sensitive to wavelength549nm yellow-green,451nm blue, and649nm red light, suggesting there might be at least three types of photoreceptors in the eyes of this wasp. There was significant difference in phototactic response of S. guani between wavelength689nm red light and649nm red light, which implied the wasp can identify different wavelength lights, even those lights with similar wavelength. Furthermore, low intensities elicited an increased phototactic response, and high intensities a decreased phototactic response, under red, yellow-green and blue light which suggested the phototaxis behavior of S. guani is intensity preference. Under three most sensitive monochromatic lights, relative light intense caused the maximum of phototactic response of S. guani in the following order: red, yellow-green and blue light. 4Phototactic characteristics of Dinotiscus armandiD. armandi was attracted to seven of nine monochromatic lights except wavelength689nm and649nm red light, which implied its broad sensitivity to the spectrum of light. D. armandi was most sensitive to wavelength340nm UV,415nm violet, and549nm yellow-green light, suggesting there might be at least three types of photoreceptors in the eyes of this wasp. Furthermore, low intensities elicited an increased phototactic response, and high intensities a decreased phototactic response, under red, yellow-green and blue light which suggested the phototaxis behavior of D. armandi is intensity preference. Under three most sensitive monochromatic lights, the relative light intense caused the maximum of phototactic response of S. guani in the following order: yellow-green, violet, and UV light.5Phototactic characteristics of Triaspis spTriaspis sp was attracted to seven of nine monochromatic lights except wavelength340nm and381nm red light, which implied its broad sensitivity to the spectrum of light. Triaspis sp was most sensitive to wavelength549nm yellow-green,451nm blue, and415nm violet light, suggesting there might be at least three types of photoreceptors in the eyes of this wasp. Furthermore, low intensities elicited an increased phototactic response, and high intensities a decreased phototactic response, under yellow-green, blue and violet light which suggested the phototaxis behavior of Triaspis sp is intensity preference. Under three most sensitive monochromatic lights, their relative light intense is similar in causing the maximum of phototactic response of Triaspis sp.The results showed that P. punctatus and its three parasitic wasps are different in phototactic characteristics both in sensitive monochromatic light and in light intensity. We could select trapping light and color specifically for P. punctatus while protect its parasitic wasps better. For example, wavelength415nm violet could be used as trapping light in P. armandi forest where a large amount of S. guani is released to control P. punctatus. In P. armandi forest where Triaspis sp is dominant parasitic wasp of P. punctatus, wavelength340nm UV can be used as trapping light for the weevil. Furthermore, light intensities of sensitive monochromatic lights are different in causing the maximum of phototactic response of P. punctatus, which implied that the trapping effect is not always positively consistent with light intensity. Thus, phototactic response of P. punctatus and its wasps to light intensity will determine power capacity of trapping light, effective space zone, and stationing intensity of light or color trapping spots.In conclusion, it’s worth emphasizing the following key points. Firstly, light trapping for P. punctatus will do some harm to its rare parasitic wasp inevitablely, due to many overlap of sensitive monochromatic lights between the weevil and three wasps. Phototactic characteristics of P. punctatus and its wasps can be used for their population monitor. For example, wavelength549nm yellow-green trapping light or color can be used for the monitor of both P. punctatus and its three wasps, because four insects are attracted to yellow-green light. If there are only three of four insects except S. Guani, wavelength415nm violet light or color can be used as trapping light or color. Secondly,, light intensity affected the phototactic behavior of insect, while low intensities elicited an increased phototactic response and high intensities a decreased phototactic response especially under UV light. The relative light intensity are different in causing the maximum of phototactic response of four insects under different sensitive monochromatic light, and the light wavelength is shorter, the light intensity causing the maximum of phototactic response is lower. Thirdly, P. punctatus was sensitive to orange, blue, green light in different sensitive order while contrasted with darkness or natural light. It implied that the visual sense of P. punctatus to the color change with environmental light intensity. The trapping effect of P. punctatus with color trapping is more consistent with the phototactic response under natural light than that under darkness. Thus, the phototactic response test of insect under natural light is more practical for diurnal insect such as P. punctatus for color trapping.