Two-cycle dynamics of alpine Parnassius smintheus (Papilionidae) butterfly populations: Host-parasitoid or consumer-resource interactions?

Long-term estimates of the population size of the alpine butterfly Parnassius smintheus have been collected from alpine meadows along Jumping Pound Ridge, Alberta, Canada. Twenty-three meadows were sampled over 11 years. Populations exhibited patterns of alternating high and low abundance in successive years. This pattern was observed across multiple meadows suggesting a consistent two-cycle type dynamic. This pattern suggests either that a natural-enemy drives the dynamics, or that caterpillar success is affected by an induced response by its food source, the lance-leaved stonecrop, Sedum lanceolatum. Two alternative mechanisms for the two-cycle dynamics, therefore, are: a host-parasitoid interaction and a herbivore-resource interaction. We construct a suite of mathematical models to investigate these interactions. Models were parameterised using the long-term field data. The level of parasitism or the plant toxin production necessary to produce the observed dynamics are estimated by the models and are used to distinguish between the proposed alternative causal mechanisms.