3 Results
Humidity, duration of heat waves, larval stage, and their interactions
did not affect adult emergence in unparasitized hosts (binomial GLM, allp > 0.05). However, in parasitized hosts, the
relative success of host and parasitoid adults was significantly
affected by experimental treatments (Fig. 2). Longer heat waves
increased the probability of host adult emergence in parasitized hosts
(Table 1), and experiencing 72 hours of heatwave in the early stage
resulted in complete mortality of parasitoids, regardless humidity
levels. Increased humidity decreased the probability of host adult
emergence (Table 1). Larval stage when the heatwaves were applied did
not affect the relative success of hosts and parasitoids, but it
positively interacted with humidity, and negatively interacted with
duration of heat waves to affect the probability of host adult emergence
(Table 1). The effect of the interaction between duration of heat waves
and larval stage on host adult emergence depended on humidity levels
(three-way interaction, Table 1). Humidity, duration of heat waves, and
larval stage did not affect the probability of no adult emergence (Table
1, Fig 2), indicating that the mortality of hosts was not affected by
the treatments, but depended on the survival of parasitoids.
The juvenile development time of unparasitized hosts increased when
experiencing longer heat waves (log-link Gamma GLM, estimates = 0.036, t
= 4.110, p <0.001, Fig. 3a), and decreased in high
humid conditions (log-link gamma GLM, estimate = -0.290, t = -7.429,p <0.001, Fig. 3a). Humidity positively interacted with
duration of heat waves to affect host juvenile development time
(log-link gamma GLM, estimate = 0.038, t = 2.976, p = 0.003). For
parasitoids, experiencing heat waves at a later stage decreased juvenile
development time (log-link Gamma GLM, estimate = -0.068, t = -2.123,p = 0.036, Fig. 3b), if they survived from heat stress. Neither
humidity nor duration of heat waves affected the juvenile development
time of parasitoids individually, however, increasing heat wave
durations in the 5th instar stage decreased juvenile
development time (log-link Gamma GLM, estimate = 0.035, t = 2.177,p = 0.031, Fig. 3b). The mid femur length of unparasitized hosts
increased if hosts developed in high humidity (log-link gaussian,
estimate = 0.189, t = 5.100, p < 0.001, Fig. 4a) or
experiencing heat waves at later stage (log-link gaussian, estimate =
0.081, t = 2.206, p =0.029, Fig. 4a). Moreover, humidity
negatively interacted with duration of heat waves (log-link gaussian,
estimate = -0.142, t = -2.871, p =0.005), and larval stage
(log-link gaussian, estimate = -0.050, t = -3.901, p <
0.001, Fig. 4a) to affect the mid femur length of unparasitized hosts.
The hind tibia length of parasitoids increased if hosts developed in
high humidity (log-link gaussian, estimate = 0.144, t = 3.032, p= 0.003, Fig. 4b), or experienced heat waves during the
5th instar stage (log-link gaussian, estimate = 0.082,
t = 2.246, p = 0.026, Fig. 4b). Larval stage negatively
interacted with duration of heat waves to affect the hind tibia length
of parasitoids (log-link gaussian, estimate = -0.048, t = -2.577,p = 0.011).
Larval stage and duration of heat waves directly affected the survival
time of hosts, but not the size of parasitoids (Fig. 5). Instead, the
hind tibia length of parasitoids was negatively correlated with host
survival time (Fig. 5), suggesting an indirect effect of larval stage
and duration of heat waves on the size of parasitoids. All the paths to
parasitoids were constrained to a global estimation (p> 0.05, more in Appendix Table S1), indicating that the
effect of heat waves and hosts did not depend on humidity. However, the
unconstrained paths to hosts indicated that the effect of heat waves on
host survival time depended on humidity levels (p<0.05, Appendix Table S1 and S2). In low humidity conditions,
host survival time was affected by larval stage and duration of heat
waves, whilst it was only affected by duration of heat waves in high
humidity conditions.