IMPACT OF ELEVATED CO2 AND TEMPERATURE ON TRITROPHIC INTERACTIONS OF Zea mays (L.), Rhopalosiphum maidis (F.) AND Menochilus sexmaculatus (Fab.)
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Date
2019
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ACHARYA N G RANGA AGRICULTURAL UNIVERSITY, GUNTUR
Abstract
Studies on ‘Impact of elevated CO2 and temperature on tritrophic interactions of Zea mays (L.), Rhopalosiphum maidis (F.) and Menochilus sexmaculatus (Fab.)’ were conducted during 2016-2018 at ICAR - Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad, Telangana. The growth and development of three successive generations of R. maidis on maize grown under elevated and ambient concentrations of CO2 (550 and 380 ppm ± 25 ppm, respectively) at six constant temperatures of 20, 25, 27, 30, 33 and 35 ± 1oC were studied. Under eCO2 conditions across the temperatures the concentrations of nitrogen (4.97-7.30%), amino acids (14.01-17.40%) and proteins (6.39-11.03%) were lower compared to that at aCO2 conditions but the concentrations of carbon (1.08-1.63%), C: N (6.96-9.26%), tannins (5.196.13%), total soluble sugars (TSS) (2.47-6.81%), starch (3.67-5.63%), carbohydrates (3.08-6.93%) and total polyphenols (12.86-16.95%) were higher under eCO2 conditions compared to that at aCO2 conditions.
Elevated CO2 and temperature significantly extended the duration of reproductive time (19.96-23.32 days) with highest fecundity (83.20-87.68 nymphs per female) whereas the development time (6.60-7.16 days) and total life cycle (26.96-29.92 days) were declined compared to that at aCO2 and temperatures in R. maidis across the three generations. The first instar nymphal weight was significantly increased with temperature in the range of 20oC to 27oC (3.67-3.85 µg day-1) but significantly declined at 30oC to 35oC (1.87-2.78 µg day-1) under eCO2 compared to aCO2 conditions across the three generations.
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Mean relative growth rate of R. maidis was significantly increased with temperature in the range of 20oC to 35oC (0.269 to 0.464 µg µg-1 day-1) under eCO2 compared to that of aCO2 conditions across the three generations.
The durations of different stages and life table parameters of R. maidis were studied under the two levels of CO2 conditions at 20, 25, 27, 30, 33 and 35°C temperatures. The durations of first (3.00 to 1.00 days), second (1.92 to 1.00 days), third (1.08 to 1.00 days), fourth nymphal instar (1.00 day), adult (23.1 to 1.20 days) and total developmental periods (29.84 to 5.36 days) decreased from 20 to 35°C temperature under eCO2 conditions compared over aCO2 conditions. Intrinsic rate of increase (rm), finite rate of increase (λ), net reproductive rate (Ro), gross reproductive rate (GRR) and mean generation time (T) of R. maidis increased significantly with temperatures ranging from 20-27°C and declined with further increase in temperature and were found to have nonlinear relationship with temperature. Reduction of ‘T’ was observed from maximum of 17.29 days at 20°C to minimum 5.57 days at 35°C. The future pest status based on Providing Regional Climates for Impacts Studies (PRECIS) A1B model showed increased rm and λ with varied Ro and reduced T of R. maidis at 6 maize growing regions of India.
The durations of different growth stages of M. sexmaculatus were studied under the two levels of CO2 conditions at 20, 25, 27, 30, 33 and 35°C temperatures. The durations of egg (5.92-2.00 days), first (3.92 to 1.04 days), second (4.08 to 1.92 days), third (2.92 to 1.00 days), fourth instar (4.84 to 2.04 day), adult longevity (56.84 to 32.91 days) and total developmental periods (71.84 to 36.68 days) decreased from 20 to 35°C temperature under eCO2 conditions compared to aCO2 conditions. The adult predation efficiency of M. sexmaculatus (2982.84 day-1) was increased under eCO2 and temperatures. The impact of eCO2 and temperatures on maize plant height (1.22-3.20 m), number of leaves (6.20-14.60 no. per plant), total leaf area (153.66-196.33 cm2), specific leaf weight (0.084-0.104 g cm-2), total biomass (322.61-675.6 g) and energy value (24.14-28.55 KJ g-1) were increased compared to that of aCO2 and temperatures where as leaf water content (74.67-64.55%) was decreased compared to that aCO2 and temperatures.
Significantly decreased nitrogen, amino acids and proteins leading to extended nymphal duration, highest MRGR and fecundity of aphids while increased carbon, carbon to nitrogen (C: N) (modify the feeding behaviour), total soluble sugars (cues in sieve element location), starch and carbohydrates enhanced the nutritional quality of maize foliage and increased growth and development of R. maidis was observed under eCO2 and temperatures. Increased tannins and total polyphenols in maize foliage showed antifeedance and indigestibility to R. maidis grown under eCO2 and temperatures.
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D5920
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