Fluctuating thermal regime preserves physiological homeostasis and reproductive capacity in Drosophila suzukii

Drosophila suzukii, an invasive species recently introduced in Europe, lays eggs in thin-skinned fruits and causes huge financial losses to fruit growers. One potential way to control this pest is the sterile insect technique (SIT) which demands a large stock of reproductive females to produce millions of sterile males to be released on demand. Unfortunately, Drosophila stocks age quickly, show declining fecundity when maintained at warm temperatures and conversely, they die from chill injury if they are maintained at constant low temperature. Here we investigate the potential of fluctuating thermal regime (FTR) as a storage method that harness the benefits of both warm and cold storage. Using a FTR with a daily warm period (1 h 20 at 25 degrees C) and cold period (20 h at 3 degrees C), interspaced by gradual heating and cooling, we compared longevity, fecundity and physiological condition between FTR females and females exposed to constant 25 degrees C and 3 degrees C. As hypothesised, FTR flies experienced much slower senescence (> 3-fold increase in lifespan) and they preserved fecundity to a much higher age than flies from constant 25 degrees C. Flies maintained at constant 3 degrees C quickly died from chill injuries caused by a gradual loss of ion and water balance. In contrast, FTR flies were able to maintain ion and water balance (similar to 25 degrees C flies) as they were allowed to recover homeostasis during the short warm periods. Together these results demonstrate that FTR represents a useful protocol for storage of Drosophila stocks, and more broadly, this shows that the benefits of FTR are tightly linked with the insect ability to recover physiological homeostasis during the short warm periods.