| A major migratory agricultural pest,Spodoptera frugiperda(J.E.Smith),has invaded China since 2019,posing a serious threat to agricultural production and food security in China.It has the characteristics of many host species,wide suitable area,strong resistance and reproductive capacity,etc.,and has obvious competitive displacement advantage to a variety of indigenous insects.However,it has not been reported yet that such a competition and substitution phenomenon could take place between S.frugiperda,S.exigua and S.litura.In this study,we chose S.frugiperda-maize-S.exigua and S.litura as a research system,as based on the S.frugiperda has obvious interspecific competition advantage to S.exigua and S.litura.We further explored that the effects of plant induced defense and mutual natural enemies have an impact on the interspecific competitive.The results of this study are of great significance for revealing the competitive replacement mechanism of S.frugiperda to S.exigua and S.litura,and further exploring the invasion mechanism of S.frugiperda.The results are as follows:1.The population dynamics of S.frugiperda,S.exigua and S.litura at maize seedling stage in the experimental field in Dehong prefecture,Yunnan province were investigated in 2019 and 2020,respectively.The results showed that the three species of insects on maize often occured in the same ecological niche and had similar seasonal activity time.The population dynamics of the three species of insects were as follows:at the early stage of maize seedling,the populations of S.exigua and S.litura were more than those of S.frugiperda.With the increase of S.frugiperda,the populations of S.exigua and S.litura showed a decreasing trend,and occurred sporadically in the later stage.2.Different possession of resources order had different effects on the population dynamics of the three species of insects.No matter which of the three insects occupied the resource space first or both at the same time,with the prolongation of time,the S.frugiperda maintained the superiority of the population,S.exigua and S.litura were gradually replaced.Measurement results show that the niche width of S.frugiperda on maize was the largest(0.9157),followed by S.litura,and the smallest was S.exigua,indicating that it had a stronger competitive advantage on maize.Moreover,the niche overlap index,niche similarity ratio and interspecific competition coefficient of S.frugiperda and S.litura were all higher than those of S.frugiperda and S.exigua,indicating that the intensity of interspecific competition between S.frugiperda and S.litura was stronger than that between S.frugiperda and S.exigua.3.Population parameters of three insects feeding on healthy and damaged plants were compared by using the age-stage,two-sex life table.The results showed that the defense response induced by S.exigua and S.litura had no significant effect on the growth and reproduction of S.frugiperda,but the defense response induced by S.frugiperda had significant effect on the growth and reproduction of S.exigua and S.litura.Meanwhile,we also explore the selectivity of infancy larvae to damaged maize leaves.The results showed that infancy larvae of S.frugiperda was attracted by the maize leaves of S.frugiperda damaged.The newly hatched larvae of S.exigua and S.litura preferred to feed on the maize leaves damaged by them,respectively.4.The field investigation showed that Microplitis similis could simultaneously parasitic the larva of S.frugiperda,S.exigua and S.litura.The Y-shape olfactometer was used to determine the behavior selection of M.similis to volatiles collected from the maize induced by the three pests’ damage.The results showed that compared with the volatiles from the healthy plants,the M.similis was attracted by the volatiles from damaged plants.However,there was no significant difference in the behavior selection of volatiles collected from the maize induced by two pests. |
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