Effects of elevated CO2 concentration on interspecific competition of larvae of Spodoptera frugiperda and Spodoptera litura on wheat and artificial diets
The increase in atmospheric CO2 concentration has direct and indirect effects on the occurrence and harm caused by insects,which can impact the destructive potential of invasive pests and their interactions with local species.However,the specific effects of increasing CO2 concentration on the competition between the invasive species Spodoptera frugiperda and its local relative Spodoptera litura are still unclear.In this study,we investigated the impact of elevated CO2 levels(400 and 800 μL/L)on interspecific competition by feeding mixed populations of S.frugiperda and S.litura with wheat and artificial diets in different ratios(25/5,20/10,15/15,10/20,and 5/25,respectively).The findings of the study were as follows:(1)S.litura experienced 100％mortality in all mixed populations under different CO2 treatments,with higher CO2 concentrations resulting in shorter time to death.The shortest time(4 days)was observed in the 25/5 and 20/10 wheat-based mixed ratios.(2)S.frugiperda exhibited significantly higher average survival days compared to S.litura in all mixing ratios.Among the different mixing ratios,the average survival days of S.frugiperda showed the most significant difference when wheat was used as food under elevated CO2 concentration,ranging from 5.21 to 6.96 days.Both S.frugiperda and S.litura had higher average survival days relative to the control group under high CO2 concentration,ranging from 1.08 to 1.31 times of normal CO2 concentration.(3)S.frugiperda had a higher average relative growth rate than S.litura under both CO2 concentrations,and both species exhibited higher growth rates compared to the control group under elevated CO2 concentration.Specifically,when feeding on artificial diets,the ratio of 25/5,20/10,and 15/15 showed growth rates that were 168.03,3.38,and 2.91 times higher,respectively,than the normal CO2 concentration.In conclusion,S.frugiperda demonstrated a significant competitive advantage over S.litura in interspecific competition under both CO2 concentrations,regardless of the type of diet provided.This advantage was particularly pronounced under elevated CO2 concentrations,favoring S.frugiperda's competitiveness.These findings contribute to our understanding of how increasing CO2 concentration affects the population adaptability of invasive species like S.frugiperda.
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