The Direct Effects Of Elevated CO₂ On Fitness And Gut Microbes Of Helicoverpa Armigera

To precisely quantify the long-term and direct effects of elevated carbon dioxide?CO₂? on phytophagous insects,this study measured the developmental time, survival,fecundity and consumption data of Helicoverpa armigera ?H. armigera? reared on artificial diet under the three different atmospheric CO₂ concentrations ?380 ?l/L, 550?l/L, and 750 ?l/L?. We collected data at six different generations ?F1, F3, F6, F9, F12,and F15?. Data was analyzed using the age-stage, two-sex life table. The population size and consumption was projected based on based on the two-sex life stable and age-stage-specific consumption. The metabolic enzyme activities of larvae of H. armigera at F1 and F15 were tested. Besides, we investigated the diversity of H. armigera larvae midgut microbiota based on the method of 16S rRNA sequencing. We also explored the functional identification of H. armigera midgut microbiota using KEGG pathways. Our study would provide information on the projection of population dynamics and help to understand the adaptive mechanism, which may provide guidance in the integrated pest management. The main result are as follows:1 Developmental time, reproduction and weight of pupa of H. armigera in response to elevated CO₂Our results revealed that developmental time of larvae was significantly delayed under two elevated CO₂ treatment, and pupa duration of female under 750 ?l/L was significant longer than other two CO₂ treatments. No significances difference were observed in the developmental time of larvae and pupa between 380 ?l/L and 550 ?l/L with the increase of generation. The developmental time of 5th -6th instar of larvae under 550 ?l/L at F15 was significantly shorter than the ambient CO₂ treatments, but the developmental time of larvae reared on 750 ?l/L was significant longer than the ambient CO₂ treatments. The duration of female and male pupa under 550 ?l/L was shorter than those under 380 ?l/L, and it significant shorter than ambient CO₂ at F15. The female adult was more sensitive to the elevated CO₂ than male adult, and the longevity of female under elevated CO₂ was significantly lower than ambient CO₂ except for F9. The fecundity of per female was significantly decreased under elevated CO₂ except for F1 and F9. No significances were observed in the pupal weight of H. armigera under the elevated CO₂ compared with the ambient CO₂ treatments with generation increasing, which higher than the ambient CO₂ treatments after F9. -The intrinsic rate of increase and finite rate of H.armigera under the 550 ?l/L at F1, F9, F12, and F15 was significantly lower than the ambient CO₂ treatments. However, the intrinsic rate of increase and finite rate of H.armigera under the 750 ?l/L was significantly lower than the ambient CO₂ treatments except F9. The net reproduction rate of H. armigera was decreased under elevated CO₂.2 The consumption of H. armigera in response to elevated CO₂Our results presented that elevated CO₂ have effects on consumption of H. armigera.The net consumption rate, transformation rate, and finite rate of H. armigera under elevated CO₂ was increased. When we project the population size and consumption of H.armigera for 60 days combined with life table data, we found that the population size and consumption of H. armigera under elevated CO₂ was lower than those reared on ambient CO₂. However, the direct effects of 550 ?l/L on H. armigera were reduced over time, and no significances were observed in growth rate and consumption rate compared with ambient CO₂.3 Metabolic enzyme activities of H. armigera in response to elevated CO₂No significances were observed in surcase activity and catalase ?CAT? activity of larvae reared under the three CO₂ concentrations. The alkaline phosphatase ?AKP?activity of larvae was significantly increased under elevated CO₂. The superoxide dismutase ?SOD? activity was significantly increased at F15 relative to ambient CO₂. The glutathione sulfurtransferase ?GST? activity was reduced, and no significances were observed in the acetylcholine esterase ?AChE? activity and carboxylesterase ?CarE?activity of larvae reared on elevated CO₂ compared with ambient CO₂.4 Diversity of midgut microbiota of H. armigera in response to elevated CO₂The results suggested that the species and abundance of midgut microbiota of H.armigera was different among three CO₂ treatments. The Firmicutes is the highest abundant bacteria in H. armigera midgut, and the second is Proteobacteria. The genus of Lactococcus and Pseudomonas dominated the phylum of Firmicutes and Proteobacteria,respectively. The three genus of Bacillus, Geobacillus, and Streptococcus also comprised large proportion compared with other species. The functional analysis shown that the midgut microbiota may play an important role in the production of amino acids and degradation of toxic substance, which need further examnation.We concluded that elevated CO₂ have strong direct effects on fitness of H. armigera,especially 750 ?l/L. The mean generation time of H. armigera reared on 550 ?l/L become shorter with increase of .generation, and the population size and consumption was higher than that reared on ambient CO₂ treatment in short time. Therefore, we predicted that the number of generations of H. armigera in a year may increase. The mechanisms underlying the adaption of H. armigera in response to changing CO₂ concentration are difficult to determine without further experimentation.