Impact of elevated temperature and carbon dioxide on foraging behaviour of Apis cerana F. in oilseed ecosystem
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Date
2019-12
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Abstract
Climate change associated with rise in concentration of atmospheric carbon dioxide and temperature is expected to affect the activity of pollinator and crop production. Oilseeds are an important component of the agricultural produce, next to food grains. The impact of elevated temperature and carbon dioxide on foraging behaviour of Apis cerana F. in oilseed (rapeseed var. TS-38 and sesamum var. ST-1683) ecosystem was studied separately in two experiments using Carbon Dioxide Temperature Gradient Tunnel (CTGT) and Open Top Chamber (OTC) established at Department of Crop Physiology and Department of Entomology, Assam Agricultural University, Jorhat during 2016-2019. In the first experiment four levels of CO2 (2 ambient at 400 ppm each and elevated of 550 ppm and 650 ppm) and 4 levels of temperature (2 ambient, +2°C and +4°C) and in the second experiment 4 levels of CO2 (2 ambient at 400 ppm each and elevated of 550 ppm and 650 ppm) and 4 levels of temperature (2 ambient, +3°C and +3°C) were used to assess the impacts of elevated temperature and CO2 levels on foraging behaviour of Apis cerana F. in rapeseed and sesamum ecosystem. No anesthetic effect was found on Apis cerana when exposed to different concentrations of CO2 viz., 0.04%, 0.05% and 0.065% for 3 minutes, 15 minutes and 30 minutes. The interactive effect of elevated temperature and CO2 on maximum frequency of flower (rapeseed) visit by Apis cerana was recorded in CTGT III (13.92±0.23) at 0800-0900 hours of the day whereas time spent per flower (6.12±0.17 seconds) at 1000-1100 hours of the day, time taken per trip (47.37±0.47 minutes) and pollen load per trip (7.87±0.12 mg) was recorded in field condition (ambient condition) compared to CTGT III (650 ppm CO2, +4°C). The time taken per trip (F=44.1000, P < 0.0001) and pollen load per trip (F=189.5555, P < 0.0001) varied significantly. Similar results were observed in sesamum also with maximum frequency of flower visit by Apis cerana (9.08±0.13) at 0800-0900 hours of the day, time spent per flower (7.20±0.10 seconds) at 0900-1000 hours of the day, time taken per trip (28.91±0.51 minutes) and pollen load per trip (6.11±0.11 mg) was
recorded in field condition (ambient condition) compared to OTC III (650 ppm CO2, +3°C). The highest bee mortality rate of 9.46% was recorded in CTGT III followed by 6.57% (CTGT II) and 3% (CTGT I) during the investigation period. The plant height increased with elevated temperature and CO2 whereas the yield attributing parameters like number of siliqua and capsules per plant, number of seeds per siliqua and capsules and 1000 seed weight of rapeseed and sesamum decreased with elevated temperature and CO2 condition. However, with elevated temperature and CO2 level, the stover yield of rapeseed and sesamum were increased whereas harvest index (HI) decreased significantly. The yield was reduced significantly (F= 61.9680, P < 0.0001 and F= 16.2102, P < 0.0001) with elevated temperature and CO2 condition and the highest yield of rapeseed and sesamum was recorded in field condition (10.05±0.23 q/ha and 7.58±0.27 q/ha) compared to CTGT III (6.03±0.23 q/ha and 5.06±0.27 q/ha). Reduction in crop yield at increased temperature and CO2 was mainly attributed to reduction in foraging activity of A. cerana, number of siliqua and capsules per plant, number of seeds per siliqua and capsules, 1000 seed weight and harvest index. The present study revealed that elevated temperature and CO2 level could decrease the foraging activity of pollinator and crop yield.