Heatwave-Like Events During Development Are Sufficient to Impair Bumblebee Worker Responses to Sensory Stimuli

Abstract

Heatwaves are increasingly common globally and are known to have detrimental impacts on animal morphology and behaviour. These impacts can be severe, especially if heatwaves occur during development, even on animals that can regulate the temperature of their developing young. The onset and duration of heatwaves are stochastic and therefore may affect all or only part of development. In the heterothermic bumblebee Bombus terrestris, elevated temperatures over the entirety of development cause morphological changes in adults, despite their capability to regulate brood temperature. However, the effects of heatwaves that occur during a short period of development are unclear. We test the impact of elevated developmental temperature during the latter fraction of development on the behaviour and morphology of adult worker B. terrestris. We show that exposure to elevated temperature over a portion of late development is sufficient to impair the initial behavioural responses of workers to various sensory stimuli. Despite this, exposure to elevated temperatures during a period of development did not have any significant impact on body or organ size. The negative effect of elevated developmental temperatures was independent of the exposure time, which lasted from 11–20 days at the end of the workers’ developmental period. Thus, heat stress in bumblebees can manifest without morphological indicators and impair critical behavioural responses to relevant sensory stimuli, even if only present for a short period of time at the end of development. This has important implications for our understanding of deleterious climactic events and how we measure indicators of stress in pollinators.

Short‐term exposure to heatwave‐like temperatures affects learning and memory in bumblebees

“…The effects of exposure to high ambient temperatures even for just a portion of development may ultimately lead to changes in behaviour. For example, B. terrestris workers that were exposed to 33°C during just a portion of their development displayed more maladaptive responses to basic stimuli, such as sucrose solution or light, than those that experienced a constant temperature of 26°C throughout their development (Perl et al, 2022). The ability of workers to forage efficiently is central to the survival of bumblebee colonies but the relationship between exposure to elevated temperature (either ambient or during development) and foraging behaviour remains poorly explored for now (e.g.…”

Subtle morphological changes in the visual and antennal sensory system of bees and wasps across an urbanisation gradient

“…This is in line with what found in ants reared at different temperatures which did not show variations in the ommatidium diameter 61 . Similarly, bumblebees reared at different temperatures did not show any difference between the mean eye area 62 . Interestingly, H. scabiosae is the species in which the body size has the strongest effect on the visual morphometric parameters.…”

Heatwaves increase larval mortality and delay development of a solitary bee

“…Thermal stress from heatwaves can cause catastrophic losses of animals and plants through direct mortality at different life stages (Breshears et al, 2021; Jørgensen et al, 2022; McKechnie & Wolf, 2010; Smale et al, 2019), as well as through sublethal impacts on reproduction, lifespan and behaviour (Hansen, 2009; Piatt et al, 2020; Zhang et al, 2018; Zhao et al, 2020). As ectotherms, insects may be especially vulnerable to heatwaves, which impact their behaviour, development and survival (Abarca et al, 2019; Harvey et al, 2020; Hemberger et al, 2023; Kingsolver et al, 2021; Perl et al, 2022; Sales et al, 2018). Many insects live at or near their thermal maximum, so sudden increases in temperature can be lethal or greatly affect physiology (Deutsch et al, 2008; Vasseur et al, 2014).…”