| Pest control method by the light traps plays an important role in IPM.To improve efficiency of light traps,it is very important to seek out sensitive wavelengths of light sources that attract targeted insect pests for using as the light sources in the light traps.Response levels of phototactic behaviors in insects to an artificial light differ according to the optical characteristics of the light sources and physiological status of the insects,and sensitivity of wavelength causing a strong phototactic behavior is species-specific.Furthermore,the artificial light can result in biochemical,physiological,and biological characteristic changes in insects.The oriental armyworm,Mythimna separata Walker?Lepidoptera:Noctuidae?,is an important agricultural insect pest,causing damage to many crops including wheat,corn,rice,etc.It is well known that M.separata moths have the phototactic behavior to light,but the sensitive wavelength and phototactic reason of M.separata moths are still unclear.In the present study,we tried to look for a sensitive wavelength of LED?light-emitting diode?light that causes strong phototactic behavior in M.separata moths,and to evaluate several abiotic and biotic factors affecting the phototactic behavior of the moths.In addition,we assessed effects of LED light with the wavelength causing the strong phototactic behavior,on energy metabolism,antioxidant enzymes,juvenile hormone and biological characteristics in M.separata.Our findings provided the scientific data to explain a reason for phototactic behavior in nocturnal insects,and to develop an effective light trap for M.separata moths.1.Phototactic response of the oriental armyworm,Mythimna separata,to LED lights of different wavelengthsThe phototactic response levels of M.separata moths to LED light sources with different wavelengths were evaluated.Our results showed that green?520 nm?LED light resulted in significant phototactic response of M.separata adults compared to the other LED lights with different monochromatic wavelengths.Experiment under the optimum conditions based on the previous experimental results revealed that the green LED light exhibited the strongest attraction rate by 64.44%among all experimental groups.Additionally,the green LED light had stronger phototactic behavior in the moths than LED lights with unclear-monochromatic wavelengths and combined wavelengths.An experiment performed in a net setup also showed that green LED light had the highest phototactic behavior of M.separata adults,1.7 times more than the commercial black light used as a control.These findings clearly demonstrate that M.separata adults have a high sensitivity to the green wavelength.Therefore,a light trap equipped with green LED light could be useful for monitoring and controlling M.separata moths.2.Influence of several factors on the phototactic response of the oriental armyworm,Mythimna separata,to green LED lightSeveral abiotic and biotic factors that affect the phototactic response levels of M.separata moths to the green?520 nm?LED light are estimated.When M.separata moths were exposed to the green LED light with light intensity of 200 lux?P=0.038?for an exposure time of 40 min?P=0.003?,attraction rate of the moths to the green LED light was the highest as compared to the other groups.The phototactic responses of the moths were significantly influenced by several biotic factors,including adaption time in darkness,age,mating status and sexuality.Three-day-old moths?P=0.001?,moths adapted to darkness for 2 h?P=0.000?,unmated male?P=0.003?and mated female moths?P=0.001?showed a significantly higher phototactic behavior to the green LED light compared to the other corresponding groups.In accordance to these data,we suggest that light trap with the green LED light for monitoring and controlling M.separata moths could be affected by several abiotic and biotic factors.3.Influence of green LED light on several enzymes involved in energy metabolism in the oriental armyworm,Mythimna separataActivities of several enzymes involved in the energy metabolism,such as glyceraldehyde-3-phosphate dehydrogenase?GAPDH?,glycerol-3-phosphate dehydrogenase?GPDH?,lactate dehydrogenase?LDH?and 3-hydroxyacyl-CoA dehydrogenase?HOAD?,and a ratio of HOAD to GAPDH activity in M.separata moths exposed to the green?520 nm?LED light for different exposure times were assessed.When M.separata moths were exposed to the green light for 30min,the activities of the two enzymes?GPDH and HOAD?and the ratio of HOAD to GAPDH activity significantly elevated?P<0.05,respectively?.The activity of LDH significantly increased in the moths exposed for 60 min?P=0.000?.Furthermore,significant differences in enzyme activities between the male and female moths were recorded in 45 min exposure time group of the GAPDH,all light-treated groups of the LDH,and 45 min group of the ratio of HOAD to GAPDH activity,respectively.This study shows that when M.separata moths are exposed to the green light,the above enzymes can be activated to produce energy for starting the phototactic behavior to the green light.4.Influence of green LED light on antioxidant enzymes in the oriental armyworm,Mythimna separataInfluences of the green?520 nm?LED light irradiation on antioxidant enzymes in M.separata adults were estimated.We determined total antioxidant capacity?T-AOC?and activities of superoxide dismutase?SOD?,catalase?CAT?,peroxidase?POD?and glutathione-S-transferase?GST?in the moth bodies exposed to the green light for different exposure times?0 min to180min?.The T-AOC and activities of all enzymes,excluding GST,increased and again reduced gradually as the exposure time of the green light extended,but not the reduced levels significantly changed compared to the control levels.This study provides that the green?520 nm?LED light irradiation could induce a weak oxidative stress in M.separata moths,and the moths under the green light could restore the damage caused by this light stress.Additionally,our results show that the adaptive ability to the light stress varied according to the moth's sexuality.5.Influence of green LED light on juvenile hormone in the oriental armyworm,Mythimna separataTotal juvenile hormone?JH?levels in different developmental stages?larvae,pupae and female?of M.separata under green?520 nm?LED light illumination with different exposure periods were evaluated.We found that the JH levels in the final instar larvae?reared for 22 d?and older age pupae?eight-day-old?significantly reduced,and that of earlier age pupae?four-day-old?and adults?three-,six-,and nine-day-old?significantly increased,as an exposure time of the green light extended,compared to the control levels?P<0.05,respectively?.Additionally,the JH level of male moths differed from that of the females.We suggest show the JH level of M.separata insects can be regulated by the green light.6.Influence of green LED light on biological characteristics of the oriental armyworm,Mythimna separataWe evaluated biological characteristics of M.separata,which were reared under the green?520 nm?LED light condition in dark period.When the insects of different stages were reared under the green light for different exposure period in dark period,egg periods prolonged and hatch rates declined in egg stage,survival rates increased and developmental periods shortened in larval stage,and pupal periods shortened.Additionally,fecundities of females reduced and longevity of the moths extended,as compared to the control?P<0.05,respectively?.Change levels of these biological characteristics depended on a length of an exposure period of the green light.Meanwhile,in F1 generation of M.separata reared under the normal condition,the biological characteristics of all the developmental stages,excluding egg stage,were not significantly different from the control.These findings show that the green light environment at night?or dark period?has the obvious effect on the survival and development period of larvae,pupal period and longevity of adults in M.separata. |
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