E levels of CO 2 increase plant growth but may also increase the injury caused by some pest insects through increased feeding 22.
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Many species of insects will meet less nutritious host plants under eCO 2, which may bring both prolonged developmental times, greater larval mortality, and lower fecundity 21. Hence, insect growth and development has often been shown to be negatively correlated with eCO 2 11, 15. Both the plant nutrient content and secondary metabolites influence insect herbivore performance 20. Lower foliar N content due to eCO 2 has also been shown to cause an increase in food intake by the insects up to 40% 19. Supportive studies of the above statements include the reduced dietary quality of leaves due to reduced nitrogen (N) by 10–30% in plants grown in enriched CO 2 conditions 18.
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The plants grown under increased CO 2 levels are often characterized by lower nitrogen content, but with increased carbon-based secondary compounds 16 without affecting the production of nitrogen-containing secondary compounds 11 which is an expensive process requiring high enzymatic activity 11, 17. The C/N ratio suggests that the distribution of resources to secondary compounds is controlled by the carbon-nutrient status of a plant 11. The development, egg laying capacity, reproduction, adult longevity and population level of insect herbivores, may be affected due to the changes in host plant quality as well as quantity due to increased CO 2 concentration which impacts plant performance. The quantity of food intake by insect on diverse host plants depends on the availability plant vigor which are known to be influenced by the carbon concentration in the surrounding environment that has direct effects on the plant quality factors such as plant biomass, water content and other plant traits such as leaf area, leaf thickness, chlorophyll content, carbon nitrogen (C and N) ratio in plant tissue and the secondary compounds 14, 15. Besides these effects, reduction in transpiration rate and stomatal conductance 12, suppression of dark respiration and photorespiration are also observed with higher CO 2 levels 13. In addition, the surplus carbon is engaged in the production of secondary metabolites 10 and plant tissues like cell walls and organelles 11. Higher photosynthetic rates eventually result in carbohydrate supply beyond demand for growth, that is stored in the plants, thus increasing the plant biomass, rather than their structural mass. The utmost adverse effects of eCO 2 on plants is an increase in the rate of photosynthesis, thereby increasing the carbon fixation by leaves. The increasing CO 2 concentrations are also expected to have a direct effect on the growth, physiology, and chemistry of plants, independent of any effects on climate 7, 8, 9. Researchers have given much emphasis towards the effects of increased concentrations of CO 2 are likely to have more impact on global climate. The increase CO 2 likely to alter the biology circuitously via climate change, and directly by creating changes in growth of plant growth, chemical composition of the plant tissue as well as influence on insect herbivory s life cycle 6. Atmospheric CO 2 is on an upsurge and has reached 409.46 ppm this year, 2018, from 407.18 in 2017 5. The magnitude of elevated CO 2 ( eCO 2) levels has seriously impacted our environment by imposing a change on global climate 2, 3, 4. Similarly, eCO 2 increased insect feeding, and did alter other variables such as their biology or reproduction.Īn increased amount of greenhouse gases due to human activities has been proposed to cause the global warming 1. We conclude that the plant carbon accumulation increased due to eCO 2, causing physiological changes that decreased nitrogen content. lugens were observed in conditions of eCO 2 levels over ambient conditions. Lower survivorship and nutritional indices of N. Similarly, increase in carbon and decrese in nitrogen ratio of leaves and alterations in defensive peroxidase enzyme levels were observed, but was non-linear among the cultivars tested. The eCO 2 treatment showed significant differences in percentage of emergence and rice biomass that were consistent across the rice cultivars, when compared to the ambient conditions. As a contemplation, the feeding pattern of the brown plant hopper, Nilaparvata lugens Stål on susceptible and resistant rice cultivars and their growth rates exposed to eCO 2 conditions were analyzed. The elevated CO 2 ( eCO 2) has positive response on plant growth and negative response on insect pests.