Study On The Cannibalistic And Dispersal Behavior Of Larvae In Fall Armyworm,spodoptera Frugiperda

Spodptera frugiperda(Lepidoptera: Noctuidae)invaded China in 2019 and had established colonies in Yunnan,Guangxi and other southern provinces of China.With the further spread of S.frugiperda in China and its harmful trend becoming more and more intense,controlling S.frugiperda became an unavoidable problem in crop production in China.The larvae showed obvious cannibalistic and dispersal behavior was an important strategy to avoid cannibalism.In this study,we systematically studied the cannibalistic and dispersal behavior of S.frugiperda larvae,and analyzed the cannibalistic and dispersal ability of larvae,to provide an important basis for understanding the population rule of S.frugiperda,and improving the level of field control and prediction.The main results are as follows:(1)Under field the rate of cannibalism in three instars larvae increased with the increase of the larval density,and most of the larvae eaten were young ones,but when the larval density reached 48 larvae per plant,there was no significant difference in the ratio of the three kinds of larvae eaten.(2)In the experiment of cannibalistic intensity of S.frugiperda 4th-6th instar larvae to 1st-3rd instar larvae,the account of larvae prey decreased with the increase of the instar of the larvae being eaten.The maximum predation of6 th to 1st-3rd instar larvae were 335.6,230.3,61.1;the maximum predation of the 5th instar larvae were 218.3,122.3,31.3;the maximum predation of the 4th instar larvae were 116.3,44.6,15.7.(3)The cannibalistic rate of S.frugiperda was related to body weight,temperature,photoperiod and host plant.The rate of cannibalism increased with the increase of body weight difference,body weight is one of the decisive factors in cannibalistic behavior.In the temperature range of 15-35℃,the cannibalistic rate of the 5th instar larvae increased firstly and then decreased with the increase of temperature,and at 30℃ the rate of cannibalism was the highest,which was 55.21±3.76%.The cannibalistic behavior of larvae requires light,and under dark condition the rate of cannibalism was the lowest.The rate of cannibalism was different among the larvae feeding on different host plants,which the rate of cannibalism was the lowest among the larvae feeding on maize and the highest among the larvae feeding on Maranta arundinacea.(4)Cannibalism has a significant effect on the development of S.frugiperda larvae.The survival rate of larvae decreases with increasing numbers of cannibalistic conspecific larvae.The survival rate of treatment feeding larvae all the time was the lowest,which was 61.33±5.88%,and was significantly lower than that of the treatment feeding(5,10 and 15 larvae)and CK(P < 0.05).The pupal weight of CK was 216.53±2.71 mg,and the pupal weight of treatment feeding larvae all the time was 163.33±3.29 mg.(5)Cannibalism had a certain effect on the longevity and fecundity of S.frugiperda adults,and the longevity and fecundity of the adults decreased with the increase of the number of feeding larvae.In CK the fecundity of females was 743.14±36.32,and the longevity of males and females were 11.39±0.45 d and 11.79±0.46d;In treatment feeding 5 larvae,the fecundity of females was697.58±47.54,and the longevity of males and females were 10.76±0.43 d and10.64±0.58d;In treatment feeding 10 larvae,the fecundity of females was684.03±42.93 and the longevity of males and females was 9.85±0.51 d and8.64±0.34d;In treatment feeding 15 larvae,the fecundity of females was634.38±45.03 and the longevity of males and females were 10.14±0.62 d and8.01±0.44d;In treatment feeding larvae all the time,the fecundity of females was 293.15±33.13,and the longevity of males and females were 7.69±0.67 d and 5.63±0.39 d,which decreased significantly.(6)In field the newly hatched larvae had two modes of dispersal: crawling dispersal and spining dispersal.In seedling and trumpet stage maize,68.53±2.08% and 52.67±3.64% of the larvae spread by crawling,31.47±2.08%and 47.33±3.64% of the larvae spread by spining.The horizontal spread distance of the 4th instar larvae was 146±27.71 cm,and the rate of returning plant was 83.33±6.45%.