Physiological&Molecular Response Of Green Peach Aphid （Myzus Persicae） To Heat Stress And Elevated CO₂

Insect populations and dispersal can be affected by temperature changes.Insects are exposed to a variety of biotic and abiotic stresses（like fluctuating temperature and increased CO₂）that can have an impact on their survival.Many of these stressors have an impact on cellular metabolism,resulting in an increase in reactive oxygen species accumulation（ROS）.As a result,insects will enhance antioxidant activity and heat shock protein（HSPs）production in response to these stresses.The management of insect pests under different temperatures has become an interesting area of study due to their ability to stimulate defense mechanisms against heat stress.This research was conducted to determine the effect of short-term heat stress exposure on life table parameters of two generations（F₁ and F₂）of the green peach aphid,Myzus persicae（Sulzer）（Hemiptera:Aphididae）and examined the antioxidant enzymes and heat-shock protein genes of green peach aphid（Myzus persicae）under short-time heat stress.In addition,the effect of elevated CO₂ on the development,fecundity,nutrition contents,and enzymatic activity of green peach aphid,Myzus persicae（Sulzer）（Hemiptera:Aphididae）at five generations were also examined.All experiments were conducted under laboratory conditions.（1）This study focused on the short-term heat stress at four different temperatures（27℃,30℃,33℃,and 36℃）and time intervals（1h,3h,6h,and 10h）on the growth,development,longevity,fecundity,and other population parameters of two generations of green peach aphid（Myzus persicae）.The results show that the nymph survival rate significantly decreased at 36℃ for 10h of both generations（F₁ and F₂）.The survival rate of the 1^st-4^th instar of F₁ generation decreased by an average of 85%,88.50%,85.75%,and 83.75%respectively at 36℃ for 10h compared to the control（25℃）.Similarly,the survival rate of the 1^st-4^th instar of F₂ generation decreased by an average of 83.75%,86%,82.25%,and 78.75%respectively at 36℃ for 10h compared to the control.The shortest longevity of the two generations of M.persicae was observed at 33℃ and 36℃ for 10h compared to control.The highest and lowest net reproductive rate（R₀）of F₁ and F₂ generations of M.persicae was observed at 27℃ for 1h and 36℃ for 10h.The intrinsic rate of increase（r_m）of the two generations of M.persicae reached the maximum at27℃ for 1h and the minimum at 36℃ for 10h.The highest finite rate of increase(λ=F₁,1.41and F₂,1.42 d^-1)for two generations of M.persicae was examined at 27℃ for 1h.The values of life table parameters of both generations（F₁ and F₂）of M.persicae were affected at 36℃ for10h.Our findings are important for a better understanding of M.persicae’s biological properties at different temperatures,and time intervals and can use as a major step in controlling their infestation on crops.（2）This study evaluated the role of short-time,heat stress treatments at different temperatures of 27℃,30℃,33℃,and 36℃ with an exposure time of 1h,3h,6h,and 10h on the activities of antioxidant enzymes including superoxide dismutase（SOD）,catalase（CAT）,peroxidases（POD）and also malondialdehyde（MDA）,and hydrogen peroxide（H₂O₂）.The results showed that the short-time heat stresses significantly increased the MDA content of M.persicae by 71%,78%,81%,and 86%at 36^oC for the exposure times of 1,3,6,and 10h,respectively,compared to control.The content of H₂O₂ increased by 75%,80%,85%,and 88%at 36℃ for the exposure time of 1,3,6,and 10h respectively compared to control.The SOD,POD and CAT activity increased by 61%,76%,77%for 1h;72%,83%,84%for 3 h,80%,85%,86%for 6 h and 87%,87.6%,88%for 10h at 36℃ respectively compared to control.Again,under short time heat stress the transcription levels of Hsp22,Hsp23,Hsp27,SOD,POD,and CAT genes were upregulated compared to control.Our results suggest that M.persicae increased the enzymatic antioxidants activity and heat-shock genes expression as one of the defensive mechanisms in response to heat stresses.（3）This study aimed to determine the effect of different CO₂ levels（ambient 380μL/L and elevated 550,and 750μL/L）on the development and fecundity rate of M.persicae under five generations（F₀-F₄）.The result shows that the elevated CO₂ levels（550 and 750μL/L）increased nymph duration and fecundity but decreased adult longevity in M.persicae.Under the ambient CO₂ level（380μL/L）,all of the biological parameters studied were not affected throughout five generations.On nymph duration,female fecundity,and adult longevity,there was a significant interaction between CO₂ levels and the effect of generations.A significant effect on the nymph development was observed after F₂ generation.Under elevated CO₂ level,the nymph duration increased significantly at F₄ generation from 7.4±0.3 at 380μL/L to 14.4±0.5 days at 750μL/L.Adult longevity decreased from the F₂ generation but the longevity was decreased significantly at F₄ generation by the elevated CO₂ level from 20.8±0.4（at ambient 380μL/L）to 11.3±0.8days at 750μL/L.The female fecundity was not affected by elevated CO₂ levels from F₀ to F₂generation but increased significantly at the F₃ and F₄ generations.The number of nymphs per female（fecundity）was significantly increased by the F₄ generation,from 71.1±2.4 to 77.5±1.8nymphs/female under elevated CO₂ level 750μL/L.Our results will be used to help future field experiments under climate change environments to measure the impact of elevated CO₂ on the growth and reproduction of M.persicae and other insects,as well as to determine the population fluctuations of the M.persicae.（4）This study aimed to evaluate the role of different CO₂ levels（ambient）380μL/L,（elevated）550μL/L and 750μL/L on the nutrition contents and enzymatic activity of M.persicae at five generations.The results show that the elevated CO₂ levels（550 and 750μL/L）increased total lipid,soluble sugar,and glycogen contents in M.persicae and decreased protein contents.Under the ambient CO₂ level（380μL/L）,no changes in all examined parameters were observed across five generations.The elevated CO₂ had significant effects on the contents of total protein,total lipid,and soluble sugar,starting within F₁ generation.The glycogen content increased from the F₂ generation.The glycogen content was not affected by the elevated CO₂ levels across generations even at the highest elevated CO₂ level of 750μL/L.The enzyme activity superoxide dismutase（SOD）,peroxidase（POD）,and catalase（CAT）of the M.persicae changed at each generation under elevated CO₂ levels.Our results showed that M.persicae’s nutrition and energy supply are influenced by elevated CO₂ levels.We compared the effects of CO₂ treatments on protein,glycogen,total lipid,and soluble sugar contents,as well as SOD,POD,and CAT activities in M.persicae.Our findings contribute to a better knowledge of the aphid metabolic and enzymatic processes under elevated CO₂,which will help in the development of pest control measures in the face of future climate change.Overall,our findings are important for a better understanding of biological and molecular properties of M.persicae at different temperatures and time intervals and can use as a major step in controlling their infestation on crops and also contribute to a better knowledge of the M.persicae growth,reproduction,nutrition and enzymatic processes under elevated CO₂,which will help in the development of pest control measures in the face of future climate change.This research work has provided more insight into the molecular processes underlying heat resistance in M.persicae to promote the use of heat treatments to control this pest,as well as to obtain new and comprehensive knowledge about the CO₂ function and potential role in aphid control strategies in agricultural systems.