Study On The Circadian Rhythm And Key Determinants Of Phototaxis In Trichogramma Dendrolimi Matsumura

Trichogramma dendrolimi Matsumura is a kind of egg parasitoid natural enemy which is widely used in industrial reproduction and popularization.It is widely used in the control of Lepidoptera pests.In recent years.in order to reduce the use of chemical pesticides and protect the biological diversity.light trapping technology has been widely used in the monitoring and control of agricultural and forestry pests.However,the commonly used insecticidal lamps are generally lack of selectivity,which can not only trap and kill target pests.but also kill natural enemies and other non target insects,which has become a key problem in the effective combination of biological control and physical control.Therefore.this paper systematically studied the eclosion rhythm and activity rhythm of adult T.dendrolimi.the effects of light source factors such as different LED wavelengths and light intensity at night and insect source factors such as gender on its phototaxis and internal structure of compound eye.In order to reveal the biological characteristics and the key determinant of phototaxis of T.dendrolimi,and to provide theoretical basis and technical support for the research and development of selective luring light source to protect the natural enemies of dominant species and rational use of luring light.The main research results are as follows:1.Circadian rhythmEclosion dynamics and diurnal rhythm:a total of 937 adults T.dendrolimi were observed,including 496 females and 441 males.with a sex ratio of 1.12:1.The eclosion duration was 84 h.and most of the eclosion occurred in the first 24 h after initial emergence.accounting for 84%of the total eclosion.From 0:00 to 2:00 in the morning.eclosion was most concentrated,accounting for 23.80%of the total eclosion.Activity day rhythm:the trend of activity day rhythm of female and male unisexual population and hermaphrodite mixed population was basically the same,that is,they were mainly active during the day and resting at night.The peak activity of female and male unisexual population occurred at 13:00.the percentage of active individuals were 91.11%and 92.22%,respectively,and the peak activity of hermaphrodite mixed population was at 9:00 am.and the percentage of active individuals reached 94%;The resting peak of female and male unisexual population occurred at 2:00 am.both reaching 94.44%,while that of bisexual mixed population occurred at 1:00 am,accounting for 78.33%.2.Effect of wavelength on phototropic behaviorThe phototropic behavior responses of T.dendrolimi to seven LED lights with the same intensity of 100 lux in the range of 365～665nm were measured using indoor multidirectional behavior selection device and dark treatment as control.The results showed that female and male unisexual populations and hermaphrodite mixed populations(1:1)had the highest photoattraction rates to ultraviolet light(365 nm).which were 32.48%.49.19%and 49.04%,respectively,followed by green light,and the lowest to dark.At the same wavelength,gender also had a significant effect on phototaxis.Under ultraviolet light treatment,the phototaxis of male population(49.19%)and mixed population(1:1)(49.04%)were significantly higher than that of female population(32.48%);Under green light treatment,the phototaxis of female population(18.54%)and mixed population(1:1)(14.66%)were significantly higher than that of male population(9.02%):Under orange light treatment,the phototaxis of female population(8.83%)were significantly higher than that of male population(2.66%).It is suggested that the wavelength significantly affected the phototaxis of T.dendrolimi,and the sex had an important effect on the phototaxis,which was related to the wavelength factor.3.Effect of light intensity on phototropic behaviorThe phototropic behavior responses of T.dendrolimi female and male unisexual population(1:1)to the favorite ultraviolet light and composite white light from 0.01 to 1000 lux were measured by using the indoor behavior selection device and white light as control.The results showed that the phototaxis of ultraviolet light in the range of 10～100 lux(34.11%)was significantly higher than other light intensity ranges,while white light preferred high light intensity of 100～1000 lux(50.05%).It indicates that the preference of’T.dendrolimi to ultraviolet light was not consistent with the response of white light intensity—the greater the light intensity,the stronger the tendency,but had a specific range of light intensity.The results show that the light intensity has a significant effect on the phototactic behavior.and the effect is related to the wavelength of light.4.External morphology of compound eyesT.dendrolimi has a pair of red oval compound eyes.The average number of small eyes in female and male individuals was 158 and 164,respectively.The small eyes in the central area of compound eyes are closely arranged in a hexagonal shape.while the edge areas are loosely arranged and irregular.In females.the dorsal ventral and anteroposterior length of the compound eyes were 85.02 μm.and 77.65 μm,respectively.The diameter of the central small eye was 6.97±0.55 μm,and the diameter of the marginal small eye was 7.76±0.68 μm.The dorsal ventral length and anteroposterior length of compound eyes in males were 68.63 μm and 65.21μm,respectively.The diameters of central and marginal small eyes were 5.86±0.38 μm and 5.90±0.32 μm,respectively.On the compound eye surface of’ female and male individuals,there are regular arrangement of sensory hairs,about 6～7 μm in length.There were three monocular eyes,two smaller dorsal monocular eyes and one larger median monocular eye.5,The basic structure of small eye and the effects of different light and dark treatments on the internal structure of compound eyeThe small eye of the compound eye of T.dendrolimi consists of a distal refractive organ.peripheral primary and secondary pigment cells,and proximal photoreceptor retinal cells and basal membrane.The cornea is made up of layers of thin chitin that are stacked horizontally,with a maximum thickness of 4.24±0.13 μm for female and 3.00±0.20 μm for male.The cone is a true cone formed by four cone cells,surrounded by two primary pigment cells,the width of the crystal cone gradually tapers from the distal end to the proximal end.and the diameter of the proximal end is similar to that of the rhabdom.The length of the female cone was about 11.04±0.39 pm,and the maximum diameter was 10.16±0.37 μm.while the male cone was 11.79±0.77 μm and 9.33±0.35 μm.respectively.The rhabdom is of central fused type.The female length was about 39.75±3.91μm and the diameter was about 2.56±0.09μm.The male rhabdom was 35.30±2.02μm in length and 2.29±0.14 μm in diameter.In the retinal cells,oval pigment granules were arranged parallel to the longitudinal axis of the small eye and extended to the basal membrane.A large number of pigment granules could still be seen below the basement membrane.Different light and dark treatments had significant effects on the maximum corneal thickness.the diameter.number and location of shielding pigment particles.The maximum corneal thickness under light adaptation(4.24±0.13 μm)was significantly greater than that under dark adaptation(3.60±0.02 μm);The diameter of primary pigment cytochrome granules(0.26±0.02 μm)was smaller than that of dark adaptation(0.34±0.01 μm),and the diameter of retinal cytochrome granule(0.27±0.02 μm)was larger than that of dark adaptation(0.18±0.03 μm):In the condition of light adaptation,the shielding pigment particles were distributed uniformly around the rhabdom,while in the condition of dark adaptation.they migrated to both ends of the rhabdom.The length of the small eyes,the interommatidial angle.the length and diameter of the crystal cone and the rhabdom,and the diameter of rhabdom microvilli were not affected by different light dark adaptation.The innovation of this paper is to reveal the eclosion and active daily rhythm of T.dendrolimi.identify the key determinants of phototaxis,such as light souce and insect source.These results will provide scientific basis and technical support for the protection and utilization of dominant natural enemies,the research and development of selective light source for the protection of dominant natural enemies.and the rational use of light traps.