Oviposited eggs are sensitive to experimental heatwaves

Extreme, variable heatwaves are predicted to increase in frequency under
global warming, leading to thermal stress that can be damaging to
biodiversity. Recently, it has been shown that exposure to heatwaves is
detrimental for adult insect reproduction, reducing population viability.
However, relatively little is known about how oviposited insect eggs, one
of the early stages post-fertilisation, are affected by heatwaves. Here,
we explore the impact of short- and longer-term thermal stress from
experimental heatwaves in an economically important insect model, the red
flour beetle (Tribolium castaneum). We uncovered that even short-term
exposures (of 2 and 5 hours at 30, 40, 42, 44, 46, 48, and 50 °C) resulted
in a drastic decline in the survival of oviposited eggs, a trend that was
also observed when eggs experienced longer durations (1, 3, and 5 days at
42 °C). Experiments were run independently across two labs, with results
found to be reproducible, reinforcing confidence in the findings.
Collectively, our results suggest that oviposited eggs (early embryos) may
be particularly vulnerable to heatwaves, even when the exposures are
brief.