Humidity modifies age-dependent heat wave effects in an insect
host-parasitoid interaction
Abstract
1. 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. 2. 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 4th instar 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. 3. 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. 4. 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.