Effect of alternative host species across phenological
shifts and temperature
On average, single-species treatments, with D. sulfurigaster(probability = 0.53 (95% CI: 0.43, 0.63)) and D. birchii(probability = 0.17 (95% CI: 0.12, 0.24)) had the highest and lowest
probabilities of host survival respectively, while the treatment with
both species present showed an intermediate probability of survival
(Probability = 0.29 (95% CI: 0.22, 0.38)) (Fig. S5). Parasitism rates
showed similar patterns across single (D. sulfurigasterprobability = 0.03 (95% CI: 0.02, 0.05%) and D. birchiiprobability = 0.04 (95% CI: 0.03, 0.07)) and multiple host species
combinations (sulfurigaster-birchii probability = 0.05 (95% CI:
0.03, 0.07)), with average parasitism rates being intermediate when
multiple host species were present. While average host survival rates
differed significantly among host species combinations (P <
0.05), average parasitism rates showed no differences. Thus, the average
development time, host survival, and parasitism rates of thesulfurigaster-birchii combination were comparable to the pooled
mean values of the two host species in isolation. However, the
probability of host survival varied across host species combinations and
this effect varied with temperature and phenological delay (Table S4;
Fig. S5 & Fig S6). Interestingly, each species in isolation showed
significant differences in survival across temperatures at each relative
delay, but when an alternative host species was present, host survival
rates did not significantly differ across temperatures at any relative
delay (P > 0.05). This is likely due to opposing responses
to phenological delay, temperatures, and resource competition betweenD. birchii and D. sulfurigaster. These results suggest
that within a single generation the presence of alternative host species
dampened differences in the probability of host survival and parasitism
rates across both temperatures and levels of resource competition, but
not phenological shifts.