Effects of Simulated Heat Waves on Life History Traits of a Host Feeding Parasitoid

Abstract

The frequency and amplitude of heat waves are predicted to increase under future climate change conditions. We still lack a detailed understanding of how changes in the frequency and amplitude of heat waves are linked to the life history traits and biocontrol efficiency of host-feeding parasitoids. In the present study, we simulated a series of heat waves as a function of amplitude and frequency to investigate the effects on the life history traits of the host-feeding parasitoid Eretmocerus hayati. We found that both the amplitude and frequency of heat waves significantly affected the adult phenotypes. In the low-amplitude heat wave group, the frequency of heat waves did not change the life history traits of the parasitoid; however, when the heat amplitude reached 42 °C, medium (four times/week) and high frequencies (seven times/week) of heat waves detrimentally affected these parameters. Hence, these findings suggest that to obtain optimal biological control with this parasitoid, we need to carefully monitor heat wave pattern (especially the amplitude and frequency) over the short term (usually 7–10 days) before releasing a host-feeding parasitoid.

Alternate patterns of temperature variation bring about very different disease outcomes at different mean temperatures

“…The heatwave may thus cause proportionally more stress in the parasite than the host at high temperatures, consistent with the thermal stress hypothesis, which suggests that a shift in temperature may reduce performance of either host or parasite (Paull et al, 2015). Indeed, that thermal stress can affect host and pathogen performance has been well supported (Gehman et al, 2018;Kirk et al, 2019;Schreven et al, 2017;Zhang et al, 2019). Alternatively, the observed increase in parasite burden due to heatwaves may be system-specific and not explained by differences in acclimatisation speed.…”

“…show that the heatwave has either lower or higher burden than equivalent constant temperatures. This context-dependency of heatwaves is supported further by studies in both plant-endoparasite (Schreven et al, 2017) and herbivore-parasitoid (Zhang et al, 2019) systems, which showed that the effect of a heatwave on parasite traits depended on the amplitude of the extreme event. As highlighted by a recent review (Claar et al, 2020), effects of warming events on disease traits remain difficult to generalise, and more studies and insight into underlying principles and mechanisms is needed to forecast the effect of extreme heat events on disease dynamics.…”

“…Indeed, each host or pathogen trait may have a unique dependency on temperature and it is their combined effect (that is, R 0 , disease outbreak, virulence) that is often of interest. However, while a growing body of theoretical (Kirk et al, 2020;Rohr et al, 2013) and empirical (Ben-Horin et al, 2013;Dallas et al, 2016;Gehman et al, 2018;Kirk et al, 2020;Zhang et al, 2019) studies have quantified the effect of rising mean temperatures on host and pathogen traits (such as, for example, within-host growth (Kirk et al, 2018), pathogen transmission (Kirk et al, 2019) and epidemiology (Gehman et al, 2018;Shocket et al, 2018)), the influence of variable temperature regimes such as heat waves and temperature fluctuations remains unresolved (Claar et al, 2020;Rohr et al, 2013).…”

“…For instance, diurnal temperature fluctuations have been shown to increase malaria transmission at the lower end of the thermal range (Paaijmans et al, 2010), while short-term temperature fluctuations led to reduced transmission success due to lower filtration rates in a Daphnia-pathogen system (Dallas et al, 2016). The effect of extreme heat events on host and pathogen traits is also highly variable and may depend on the magnitude, duration and intensity of the applied heatwave (Landis et al, 2012;Schreven et al, 2017;Zhang et al, 2019). In a parasitoid-insect interaction, a heatwave of 5 °C resulted in greater parasitoid development while a 10 °C increase reduced parasitoid growth (Schreven et al, 2017).…”

Heat waves affect an invasive herbivore and its parasitoid differentially with impacts beyond the first generation

“…for at least five consecutive days (De Boeck et al 2010), can cause direct mortality and can have negative fitness consequences for surviving individuals (Roux et al 2010, Bannerman et al 2011, Sentis et al 2013, Zhang et al 2019. Susceptibility to thermal stress can vary between trophic levels across a food chain (Voigt et al 2003, Hance et al 2007, Aguilar-Fenollosa and Jacas 2014.…”