| Spodoptera litura is a worldwide polyphagous and fulminant pest.The muti-generation occurrence,wide range of hosts,high level of resistance to pesticides make it a serious pest to vegetables and other crops.Due to the phototaxis of adult S.litura,light trapping technology has been used as one of the most important control method for this pest.However,the trapping rhythm of light-traps of S.litura adults is unclear,and the trapping effect of insect-trapping lamps is rarely evaluated,which limits the popularization and application of light trapping technology.In this study,the trapping rhythm of light-traps rhythm of S.litura was clarified,and the correlation between catching rhythm of light-traps behavior rhythm and reproductive behavior rhythm was analyzed.The dye marked method of adults was established,and the trapping effect of insect-trapping lamps on S.litura was evaluated using marking-releasing-recycling method.Those results provided theoretical support for the popularization and application of light trapping technology.The main results are as follows:1.Trapping rhythm of light-traps of S.litura and its behavioral basisThe results of light trapping experiment in the field showed that the trapping rhythm of light-traps behavior of S.litura exhibited obvious rhythm,and the peak time of trapping rhythm of light-traps for females was the first half of night(20:00-22:00),while that for males was the second half of night(1:00-3:00).In addition,during the whole trapping process,the number of trapped males was significantly higher than that of females,and more than 90% of trapped females were mated females.Therefore,we suggested to turn on the insect-trapping lamps at the first half of night to trap mated female S.litura,or turn on the insect-trapping lamps at the whole night to trap both male and female S.litura.The field sex pheromone trapping rhythm was highly consist with the indoor reproductive behavior rhythm,and the trapping rhythm of light-traps of male was significantly related to its sex pheromone trapping rhythm.In addition,the trapping rhythm of light-traps of male and female were significantly related to spawning rhythm and mating rhythm respectively,suggesting that the reproductive behavior rhythm of S.litura may be the reason for the formation of trapping rhythm of light-traps.The results of indoor simulation experiments showed that when there was no host shelter(directly exposed to light and felt light stimulation),both male and female S.litura showed instantaneous trapping rhythm of light-traps behavior after turning on the lamps,and trapping rhythm of light-traps mainly at the first 2 hours after turning on the lamps.In the environment with host shelter,unmated females have no obvious trapping rhythm of light-traps,while mated males and females and unmated males showed obvious rhythm.The trapping rhythm of light-traps of males and females is significantly related to spawning rhythm and mating rhythm,respectively.These results show that the phototactic behavior of S.litura does not have obvious rhythm,S.litura exposed to light immediately flight to the light because of the direct light stimulation.The reproductive behaviors of S.litura such as mating and spawning have obvious rhythms,therefor,when hosts and other obstructions exist in the field,S.litura is rhythmically exposed to the light for matching and searching for oviposition sites,and consequently caught by the light.Those results implied that the reproductive behavior rhythm of S.litura is the cause of its trapping rhythm of light-traps.2.Trapping effect of insecticidal lamp on S.lituraThe dyes and concentrations for marking S.litura adults were screened by added dyes in the diets of larvae.The results showed that Sudan Red 7B with a concentration of 0.006% could successfully label S.litura adults,and the survival rate of larvae was 72.5%.The effect of 0.006% Sudan Red 7B on the growth,flight ability and phototaxis of S.litura was further tested.The results show that 0.006% Sudan Red 7B has no negative effect on the larval survival rate,larval development duration,pupal survival rate,pupal development duration,pupal weight,adult life span,adult body length,wing spread,adult flight ability and phototaxis of adults,indicating that0.006% Sudan Red 7B can be used as an effective dye for marking S.litura.The trapping effect of trapping lamps was evaluated by releasing-recovering method of S.litura adults which marked with dyes,paints and sheared wings.The results showed that the light trapping recovery rate of S.litura at the net room where the insects can not escape was 60.9%-63.8%,and that of S.litura at the field is49.4%-51.3%.The light trapping recovery rate of S.litura at the field was80.4%-81.1% compared with that of the net room,and under open field conditions,there is a risk of predation by birds,spiders and other natural enemies.Taken together,the light trap technology has a very good trapping effect on S.litura in the field.To sum up,this study indicated that the peak time of trapping rhythm of light-traps of female and male S.litura adults was the first and second half of the night,separately.Our results showed that the reproductive behavior rhythm of S.litura was the cause of the trapping rhythm of light-traps.The dyeing and marking method of S.litura was established,and the trapping effect of insect-trapping lamps on S.litura in the field was determined by the marking-releasing-recycling method.Those results provide a theoretical basis for the popularization and application of light trapping technology,and give a practical case for establishing the evaluation system of the effect of insect-trapping lamps.Therefore,our results has important theoretical significance and application value. |
