Impact of elevated temperature and carbon dioxide on foraging behaviour of Apis cerana F in oilseed ecosystem

Abstract

Climate change associated with rise in concentration of atmospheric carbon newlinedioxide and temperature is expected to affect the activity of pollinator and crop newlineproduction. Oilseeds are an important component of the agricultural produce, next to newlinefood grains. The impact of elevated temperature and carbon dioxide on foraging newlinebehaviour of Apis cerana F. in oilseed (rapeseed var. TS-38 and sesamum var. ST- newline1683) ecosystem was studied separately in two experiments using Carbon Dioxide newlineTemperature Gradient Tunnel (CTGT) and Open Top Chamber (OTC) established at newlineDepartment of Crop Physiology and Department of Entomology, Assam Agricultural newlineUniversity, Jorhat during 2016-2019. In the first experiment four levels of CO2 (2 newlineambient at 400 ppm each and elevated of 550 ppm and 650 ppm) and 4 levels of newlinetemperature (2 ambient, +2°C and +4°C) and in the second experiment 4 levels of newlineCO2 (2 ambient at 400 ppm each and elevated of 550 ppm and 650 ppm) and 4 levels newlineof temperature (2 ambient, +3°C and +3°C) were used to assess the impacts of newlineelevated temperature and CO2 levels on foraging behaviour of Apis cerana F. in newlinerapeseed and sesamum ecosystem. No anesthetic effect was found on Apis cerana newlinewhen exposed to different concentrations of CO2 viz., 0.04%, 0.05% and 0.065% for 3 newlineminutes, 15 minutes and 30 minutes. The interactive effect of elevated temperature newlineand CO2 on maximum frequency of flower (rapeseed) visit by Apis cerana was newlinerecorded in CTGT III (13.92±0.23) at 0800-0900 hours of the day whereas time spent newlineper flower (6.12±0.17 newlineseconds) at 1000-1100 hours of the day, time taken per trip newline(47.37±0.47 minutes) and pollen load per trip (7.87±0.12 newlinemg) was recorded in field newlinecondition (ambient condition) compared to CTGT III (650 ppm CO2, +4°C). The time newlinetaken per trip (F=44.1000, P lt 0.0001) and pollen load per trip (F=189.5555, P lt newline0.0001) varied significantly. Similar results were observed in sesamum also with newlinemaximum frequency of flower visit by Apis cerana (9.08±0.13) at 0800-0900 hours of newlinethe day, time spent per flower (7.20±0.10 newlineseconds) at 0900-1000 hours of the day, newlinetime taken per trip (28.91±0.51 minutes) and pollen load per trip (6.11±0.11 newlinemg) was newlinerecorded in field condition (ambient condition) compared to OTC III (650 ppm CO2, newline+3°C). The highest bee mortality rate of 9.46% was recorded in CTGT III followed by newline6.57% (CTGT II) and 3% (CTGT I) during the investigation period. The plant height newlineincreased with elevated temperature and CO2 whereas the yield attributing parameters newlinelike number of siliqua and capsules per plant, number of seeds per siliqua and newlinecapsules and 1000 seed weight of rapeseed and sesamum decreased with elevated newlinetemperature and CO2 condition. However, with elevated temperature and CO2 level, newlinethe stover yield of rapeseed and sesamum were increased whereas harvest index (HI) newlinedecreased significantly. The yield was reduced significantly (F= 61.9680, P lt 0.0001 newlineand F= 16.2102, P lt 0.0001) with elevated temperature and CO2 condition and the newlinehighest yield of rapeseed and sesamum was recorded in field condition (10.05±0.23 newlineq/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). newlineReduction in crop yield at increased temperature and CO2 was mainly attributed to newlinereduction in foraging activity of A. cerana, number of siliqua and capsules per plant, newlinenumber of seeds per siliqua and capsules, 1000 seed weight and harvest index. The newlinepresent study revealed that elevated temperature and CO2 level could decrease the newlineforaging activity of pollinator and crop yield. newline