Insects in Fluctuating Thermal Environments

Abstract

All climate change scenarios predict an increase in both global temperature means and the magnitude of seasonal and diel temperature variation. The nonlinear relationship between temperature and biological processes means that fluctuating temperatures lead to physiological, life history, and ecological consequences for ectothermic insects that diverge from those predicted from constant temperatures. Fluctuating temperatures that remain within permissive temperature ranges generally improve performance. By contrast, those which extend to stressful temperatures may have either positive impacts, allowing repair of damage accrued during exposure to thermal extremes, or negative impacts from cumulative damage during successive exposures. We discuss the mechanisms underlying these differing effects. Fluctuating temperatures could be used to enhance or weaken insects in applied rearing programs, and any prediction of insect performance in the field—including models of climate change or population performance—must account for the effect of fluctuating temperatures.

Daily temperature extremes play an important role in predicting thermal effects

“…However, the observed demographic parameters and fitness were stable under T max ≤36°C and were much higher than predictions based on T day (Figs 2-6). This suggests that organisms can recover or even compensate for heat stress under mild temperatures during the night (Davis et al, 2006;Sentis et al, 2013;Colinet et al, 2015).…”

“…These substances, combined with excessive consumption of resources and energy in promoting heat resistance, in turn reduce performance for life history traits (Krebs and Feder, 1998;Silbermann and Tatar, 2000). Yet on the other hand, at mild night-time temperatures, organisms may spend more resources and energy on repairing and compensating performance such as development and reproduction (Davis et al, 2006;Sentis et al, 2013;Colinet et al, 2015). For example, some aphid species can buffer the negative impact of high daytime temperatures by recovering at relatively lower night-time temperatures (Ma et al, 2004a,b;Zhao et al, 2014).…”

“…Organisms in many natural terrestrial environments experience diel temperature fluctuations rather than constant temperatures (Colinet et al, 2015), including sporadic extreme conditions involving T max .…”

“…However, predictions based on short periods of high-temperature stress may neglect the effect of mild night-time temperatures (Carter et al, 1982;Zhou et al, 1989;Triltsch et al, 1998), which allow organisms sufficient time to recover during intervals of successive episodes of thermal stress (Davis et al, 2006;Sentis et al, 2013). Regimes used in previous studies on temperature fluctuations (reviewed by Colinet et al, 2015) tend to focus on the amplitude of fluctuating conditions and confound changes in T max with different daily minima, which also affect performance (Zhao et al, 2014). This makes it difficult to isolate the specific effects of changes in T max .…”

An invitation to measure insect cold tolerance: Methods, approaches, and workflow

“…Notably, acclimation under fluctuating temperatures usually leads to greater cold tolerance (Colinet et al, 2015). Although laboratory acclimation can never properly replicate field conditions, the aim of incorporating laboratory acclimation is to provide some indication of the extent of plasticity, and therefore the extent to which potential cold tolerance is being above, the enhanced cold tolerance was lost within a week of returning the insects to the rearing temperature of 30 °C (Fields et al, 1998), a process termed deacclimation.…”