The crepuscular (evening) circadian rhythm of adult spruce budworm (Choristoneura fumiferana (Clem.)) flight activity under the influence of changing evening temperatures is described using a mathematical model. This description is intended for inclusion in a comprehensive model of spruce budworm flight activity leading to the simulation of mass migration events. The model for the temporal likelihood of moth emigration flight is calibrated using numerous observations of flight activity in the moth’s natural environment. Results indicate an accurate description of moth evening flight activity using a temporal function covering the period around sunset and modified by evening temperature conditions. The moth’s crepuscular flight activity is typically coincident with the evening transition of the atmospheric boundary layer from turbulent daytime to stable nocturnal conditions. The possible interactions between moth flight activity and the evening boundary layer transition, with favorable wind and temperature conditions leading to massive and potentially successful migration events, as well as the potential impact of climate change on this process, are discussed.
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