Individual traits as drivers of spatial dispersal and infestation patterns in a host-bark beetle system

Tree-killing bark beetle species such as Ips sp. and Dendroctonus sp. are considered one of the most severe biotic hazards affecting forests at the global scale. Although spatio-temporal patterns of dispersal and infestations have been widely observed and statistically analyzed profound knowledge about the host-bark beetle interactions that evoke these patterns is scarce. We developed an individual-based and spatially explicit model - the Infestation Pattern Simulation (IPS) model - to elucidate how individual traits affect system-level dispersal and infestation patterns. IPS simulates processes including dispersal, host selection, aggregation, and finally colonization, or rejection by host defence on a local scale. Host-bark beetle interactions are implemented highly dynamically, i.e. individual adaptive behavior takes into account space- and time-dependent variations in traits. Simulations consider one dispersal wave starting from a single source located in a virtual stand. Finally, the effects of both bark beetle- and host tree-specific parameters on emerging system patterns were quantified using a one-factor-at-a-time sensitivity analysis approach. As system-level response variables we used (i) percentage of successful beetles, (ii) number of infestations, and (iii) maximum infestation distance to source. Among bark beetle-specific parameters those affecting host recognition (e.g. perceptual range, energetic level) and attack synchrony (e.g. source size, time lag between flight cohorts) were revealed to be highly sensitive with regard to all three response variables. In addition, the host tree's resistance and spatial distribution is also shown to be decisive for infestation occurrence. The model provides a conceptual framework linking individual behavior to system-level patterns. Thus it represents a powerful tool - complementing lab- and field-based approaches - which may contribute to our understanding of the complex spatio-temporal processes that govern host-bark beetle dynamics.