Wide diurnal temperature variation inhibits larval development and adult reproduction in the diamondback moth

Although thermal variability is known to influence the performance of ectotherms, there is limited information on the influence of variation in diurnal temperature range (DTR) during early developmental stages. Here we test variation in DTR ( ±0 °C, ±4 °C, ±6 °C, ±8 °C, ±10 °C and±12 °C) with a constant mean temperature (25 °C) on the larval stage of diamondback moth (DBM), Plutella xylostella (L.), and assess immediate effects on larval development and survival, and delayed effects on pupal development and survival and adult longevity and reproductive performance. Wide amplitudes ( ±10 °C and±12 °C) inhibited larval development and adult performance, but increased the proportion of eggs laid early, while moderate amplitudes ( ±4 °C, ±6 °C and±8 °C) resulted in only minor effects. Larval development rate under wide amplitudes ( ±10 °C and±12 °C) was faster than predicted by a degree-hour model. Overall, the intrinsic rate of increase of the population was lowered with increasing DTR, despite mean temperatures being the same. These findings highlight marked cross-stage effects of DTR when temperatures fluctuate substantially, likely linked to maximum temperature, and they emphasize the importance of considering DTR when assessing effects of climate warming.