Influence of warming with temperature oscillations on the life history traits of the Aphids Acyrthosiphon pisum and Megoura crassicauda

Abstract Organisms naturally experience diurnal temperature fluctuations and variable extreme environmental events rather than only static thermal regimes. Therefore, experimental studies that use only static mean daily, monthly or yearly temperatures overlook the possible influence of diurnal temperature fluctuations. Exposure to fluctuating temperatures enables an organism to perform more ‘naturally’ as they have a period of recovery, whereas under constant temperature, they do not have thermal recovery periods. This study compares the impacts of fluctuating and constant temperatures on the fitness and demographic parameters of the pea aphid, Acyrthosiphon pisum . We use four fluctuating temperature regimes that are increased by + 0°C, + 2°C, + 4°C and + 5°C from field-recorded, fluctuating base temperatures and four constant temperatures of 19°C, 21°C, 23°C and 24°C as treatments and also use a control temperature of 25°C. We find that A. pisum exhibited faster development, quicker generation time (GT), lower population doubling time (DT), increased intrinsic rate of increase (r m ) and a finite rate (λ) under warming conditions. In contrast, adult longevity, survival period, fecundity, net reproductive rate (R 0 ), age-specific survivorship (l x ) and age-specific fecundity (m x ) were negatively affected by warming. The fluctuating thermal regimes improved overall fitness and all demographic parameters of both aphid species; therefore, we identify that daily fluctuating temperatures play a vital role in monitoring and predicting natural population dynamics. These results have implications for the experimental forecasting of natural population dynamics under climate change and global warming predictions.