| The chive gnat,Bradysia odoriphaga Yang et Zhang is notorious underground pest of vegetables.it has wide range of host plants and can harm 7 families more than 30 kinds of vegetables and edible fungus,especially Chinese chive,Allum tuberosum Rottl.ex Spreng.The larvae main directly damaged the roots and bulbs of Chinese chive,which results in 40-60%loss of yield every year,even total loss sometimes.Because the use of chemical pesticides is not standardized,the quality of Chinese chive products and the safety of soil environment and the health of people are all seriously threatens for exceeding standard of pesticide residue and“poisonous Chinese chive”incidents,which usually refers to as the“No.1 killer”in the field of quality and safety of agricultural produces in China.Nowadays,new visual-mediated physical monitor and control technologies,which includes light-lamp and coloured-sticky traps,have been more and more extensive applied because of the efficient,simple and environmental-friendly characteristics.It provides a new way for controlling many agricultural and forestry pests including chive gnat,and greatly relieves the outstanding problems,such as increased resistance to pests and excessive pesticide residues caused by alone rely on chemical pesticide.However,it`s still unclear the inherent relation between colour visual information and taxis behaviour of chive gnat,therefore,the relationship of taxis behaviour of chive gnat to colour vision and its molecular mechanism were studied by experimental and molecular bio-technological methods.Our objective was to clarify the visual-mediated taxis behaviour in B.odoriphaga.And it provides the theoretical knowledge for developing the newly visual induced physical technology of monitoring and control.The main results are summarized as follows:(1)There were two obvious peaks of phototaxis in ultraviolet spectral zone of 380nm and green spectral zone of 524nm within the spectral range from 340nm to 605nm,which the phototaxis of female and male adults were 43.10 and 45.10%for ultraviolet spectral zone and the phototaxis of female and male adults were 39.85 and 37.72%for green spectral zone.There was one obvious peak of negative phototaxis in 460nm blue spectral zone within the spectral range from 340nm to 605nm,in which the phototaxis of female and male adults were 43.50 and 41.75%.In the different circadian rhythms,the results of taxis behaviour of B.odoriphaga to 7 LEDs with different wavelength in the day(9:00-11:00am)were similar to those at night(5:00-7:00 pm),but it was no significant difference.28.86%female and 25.52%male adults showed a significant preference for ultraviolet light in the day while 30.49%female and 26.85%male adults prefer ultraviolet light at night;a lesser preference to green light,the phototaxis rate of female and male were 15.89 and 19.59%in the day,while those of female and male were 17.76 and 18.26%at night;the least preference to orange light,the phototaxis rate of female and male were 9.68 and 5.55%in the day,while those of female and male were 8.88 and 6.38%at night.The phototaxis of B.odoriphaga was increased according to the increase of light intensity.Female and male significant preferred for high intensity over black and low intensity.The results showed B.odoriphaga has a phototaxis for ultraviolet and green light,and it is related to light wavelength and light intensity and irrespective of sex and circadian rhythm.(2)Those results were similar between the preference for 4 colour hues(black,green,brown and orange)and for 4 light intensities(black,dark grey,light grey and white).Chive gnats had a significant preference for black.In experiment of colour hues,female and male adults significant prefer black,and a lesser preference for green and brown,orange was less attractive.In experiment of brightness,female and male adults significant prefer black,and a lesser preference for dark and light grey,white was less attractive.The preference for colour hues and brightness were similar under different light intensity(0.1,100,1000 and 10000 mW/m~2),spectral light(blue and green lights)and different physical states(virgin and mated adults),it indicated this behaviour of preferring black can not be changed by environmental factors(spectral light and light intensity)and entomic factors(sex and physical stages).ambient light.(3)Two ultraviolet and two long-wavelength sensitive opsin genes were cloned from B.odoriphaga adult head,and named as Bo-uv1(GenBank accession number:MH491829),Bo-uv2(GenBank accession number:MK766510),Bo-lw1(GenBank accession number:MK766508)and Bo-lw2(GenBank accession number:MK766509).1542bp of Bo-uv1,1134bp of Bo-uv2,1104bp of Bo-lw1 and 1131bp of Bo-lw2 encoded opsins of varying lengths:514,378,368 and 377 amino acids,respectively.Sequence analysis found that these opsin genes were members of the G-protein-coupled receptor family and contained seven transmembrance(TM)domains.Sequence alignment revealed that Diptera opsins shared significant homology.The analysis of spatial and temporal expression showed opsin genes had spatio-temporal expression specificity which showed the highest expression in adult stage and from adult head.The expressions of Bo-uv2 and Bo-lw2 opsin genes in female head were much more than those in male head.These indicated that B.odoriphaga adults existed two kinds of opsin genes,ultraviolet and long-wavelength sensitive opsin genes,which had spatio-temporal specificity and Bo-uv2 and Bo-lw2 opsin genes showed a sex expression specificity.Based on the results of phototaxis of chive gnat adult,we speculated chive gnats had two kinds of photoreceptors contained ultraviolet and green photoreceptors.(4)The expressions of ultraviolet and green wavelength sensitive opsin genes were significant influenced by ultraviolet and green light.Ultraviolet(Bo-uv1and Bo-uv2)and green(Bo-lw1and Bo-lw2)wavelength sensitive opsin genes were increased by ultraviolet light treatment,and their expression levels were significantly higher than one of green and darkness.Besides of Bo-lw1 gene,the expression levels of other three opsin genes under green light were obviously higher than those under darkness;In the experiment of light intensity,the expression levels of different opsin genes were significant difference under the light with different intensities.Bo-uv1and Bo-uv2 opsin genes were the highest expression levels under UV light with high intensity,a lesser expression under UV light with low intensity,and the lowest expression levels in darkness.The expression levels of Bo-lw1 opsin gene were no significant under green light with different intensities,however,Bo-lw2 opsin genes were the highest expression levels under green light with high intensity,a lesser expression under green light with low intensity,and the lowest expression levels in darkness.These indicated there were intimate relationship between opsin expression level and the stimuli of wavelength and intensity.The innovation of this paper was to reveal the relationship between visual signals(light and colour)and the taxis behaviour of chive gnats from behavior and internal mechanism aspects,was confirmed that chive gnat had color vision,and existed at least two types of ultraviolet and long-wavelength photoreceptors,and the expression levels of ultraviolet and long-wavelength sensitive opsin genes were decreased by spectral light and light intensity stimuli.These findings clarify the visual-mediated mechanism of its taxis behaviour.Those provided a theoretical basis for developing efficient and green pest physical monitoring and control technologies,and had important academic value. |
