Abstract:
- Climate change is projected to increase the likelihood of extreme heat
events, but it may also alter humidity levels, leading to the
potential for coupled thermal and hydric stress. While increasing
frequency and intensity of extreme heat events have been
well-documented for their negative effects on species and their
interactions, how humidity modulates the impacts of heat waves is
currently unknown.
- We investigated how humidity interacted with heat waves of different
timings and durations to affect the life histories in an insect
host-parasitoid interaction, comprising the Indian meal moth,Plodia interpunctella , and its endoparasitoid wasp,Venturia canescens . Hosts parasitised as 4thinstar larvae and unparasitized hosts were maintained in a high humid
(60.8% RH) or low-humid (32.5% RH) environment at a constant
temperature of 28℃. They were then exposed to 38℃ heatwaves with a
duration of 6 or 72 hours in either the 4th or
5th instar.
- Humidity and heat waves did not affect the adult emergence of
unparasitized hosts, but longer heat waves and lower humidity
increased the probability that host adults emerged from parasitized
hosts, indicating the negative effect of these conditions on the
survival of parasitoids. Furthermore, juvenile development time and
body size of hosts and parasitoids responded differently to timing and
duration of heat waves, and high humidity decreased larval development
time of unparasitized hosts and increased the size of both hosts and
parasitoids. In addition, humidity negatively interacted with larval
stage and duration of heat waves to affect the size of unparasitized
hosts, but this effect was not found in parasitoids.
- Our results show that humidity modulates the life history of hosts and
parasitoids, highlighting the importance of humidity in maintaining
host-parasitoid interactions. Humidity should be considered when
predicting the impact of temperature extremes on species’ population
dynamics and their interactions.