Effects Of Elevated CO₂ Concentration On Population Growth,Interspecific Competition,and Natural Enemy Predation Of Two Species Of Noctuid Moths

The increase in atmospheric CO₂ content is one of the main reasons for global warming.As a raw material for carbohydrates produced by plants during photosynthesis,CO₂ is closely related to biological activities.It not only directly affects plants,causing changes in their nutritional composition and growth and development,but also affects herbivorous insects and their natural enemies through the food chain.This study sets the current atmospheric carbon dioxide concentration（400μL/L）and estimated carbon dioxide concentration by the end of this century（800μL/L）,to study the effects of different CO₂ concentrations on the population growth,interspecific competition,and the growth,development,and predation of Spodoptera frugiperda and Spodoptera litura,the common natural enemies of the two nocturnal moths,the Arma chinensis.The main research results are as follows:（1）Three treatments were set:direct effect（only the test insect was treated with high CO₂ concentration）,indirect effect（only the host plant wheat was treated with high CO₂ concentration）,and control（both the test insect and the host plant wheat were treated with normal CO₂ concentration）on the S.frugiperda and the S.litura.The results showed that under direct and indirect influences,the development duration of S.frugiperda was significantly shortened（P<0.05,the same below）,85.39%and 87.83%respectively for the control group;its fecundity increased by 2.02 and 3.78 times respectively as compared with the control;its pupal weight decreased by 93.78%and87.47%,respectively compared to the control group;its net proliferation rate（R₀）,intrinsic growth rate（r_m）and perimeter growth rate（λ）increased,1.48 times and 3.02times,1.11 times and 1.32 times,1.02 times and 1.06 times respectively,compared to the control;and its average generation cycle（T）and population doubling time（DT）were shortened by 95.35%and 90.93%,89.65%and 77.66%respectively for the control group.In S.litura,its developmental period was only shortened under direct influence,accounting for 88.88%of the control;fecundity decreased under direct and indirect influences,which were 48.02%and 68.82%of the control respectively;the pupal weight significantly decreased under indirect influence,accounting for 85.31%of the control,net proliferation rate（R₀）,intrinsic growth rate（r_m）and perimeter growth rate（λ）were decreased,accounting for 38.61%and 37.08%,77.77%and 88.88%,95%and 97.5%of the control group respectively;and average generation cycle（T）and population doubling time（DT）were prolonged under direct influence,1.15 times and 1.35 times higher than the control,respectively.Overall,the increase in CO₂ concentration,whether directly or indirectly,is beneficial for the population occurrence of the S.frugiperda,but not beneficial to the population occurrence of S.litura,whether directly or indirectly.（2）Analyze and compare the impact of elevated CO₂ concentration on the interspecific competition relationship between S.frugiperda and S.litura.The results showed that in five different mixing ratios,whether fed with feed or wheat,the mortality rate of S.litura reached 100%over time,and the required time was shorter at elevated CO₂ concentrations;in each mixed ratio,the average survival days of the S.frugiperda were significantly higher than those of the S.litura,and the relative survival days of the S.frugiperda and the S.litura were higher than the control under high CO₂ concentration,when feeding on wheat,it reached 1.08,1.22,1.26,1.31 and 1.13 times of the normal CO₂ concentration;the average relative growth rates of the S.frugiperda were higher than those of the S.litura under two different CO₂ concentrations,and the average relative growth rates of the S.frugiperda and the S.litura were higher than the control under high CO₂ concentrations,when feeding on feed,the ratio of 25/5,20/10 and 15/15was 168.03,3.38 and 2.91 times of the normal CO₂ concentration.Overall,in the interspecific competition between the S.frugiperda and the S.litura under two different CO₂ concentrations,whether fed on wheat or feed,the S.frugiperda has a strong competitive advantage,especially at high CO₂ concentrations,which is more conducive to its competitiveness.（3）The population growth parameters of the natural enemy insect A.chinensis under two CO₂ concentrations were observed and counted.The results showed that the development duration of the first generation A.chinensis under high CO₂ concentration treatment was significantly shortened（P<0.05,the same below）,only 93.43%of the control;the survival rate was significantly reduced,fecundity decreased significantly,only 26.27%of the control;the net proliferation rate（R₀）,the intrinsic growth rate（r_m）,and the weekly growth rate（λ）significantly decreased,accounting for 36.02%,82.47%,and 98.18%of the control group,respectively;the population doubling time（DT）was significantly prolonged,reaching 1.18 times that of the control.A study on the feeding capacity of the A.chinensis under two different CO₂ concentrations found that with an increase in CO₂ concentration,the feeding capacity of the A.chinensis on the S.frugiperda significantly decreased,only 94.80%of the normal CO₂ concentration,and the feeding capacity of the S.frugiperda was lower than that of the S.litura.The results of this study indicate that,firstly,the increase in CO₂ concentration in the atmosphere promotes the population growth of the S.frugiperda,but is not conducive to the growth and breeding of S.litura and A.chinensis;Secondly,the increase in CO₂concentration is beneficial for the interspecific competitiveness of the S.frugiperda;Thirdly,the ability of S.frugiperda to evade natural enemies is slightly stronger than that of S.litura;from these three aspects,it is predicted that the increase in CO₂ concentration will have a positive impact on the occurrence of the S.frugiperda.The invasive species of S.frugiperda will have stronger adaptability under high CO₂ concentration than its local relative species S.litura.