Come from away: Reconstructing a long‐range migratory flight of spruce budworm moths to Newfoundland, Canada

Insect migration can be viewed as a coordinated sequence of behaviours (take‐off, displacement and landing) controlled by physiological and environmental factors. In this study, we combined Lagrangian atmospheric models with ecophysiological factors to reconstruct a migratory flight of spruce budworm (SBW), Choristoneura fumiferana (Lepidoptera: Tortricidae) (Clem.), moths. This insect is a major defoliator in boreal forests in Eastern Canada and was captured in large numbers in a light trap on the night of 26 to 27 July 2017 at Sally's Cove, on the west coast of Newfoundland, Canada. First, we used a simple trajectory model in backward mode in time to identify the most likely source region of the SBW moths south of Anticosti Island, in the Gulf of St. Lawrence, where moth take‐off was likely facilitated by orographic lift. Second, using a thermo‐circadian model of take‐off flight and the dispersion model MLDP ( Modèle lagrangien de dispersion des particules ), we determined that during their 375 km journey, moths travelled a few hundred metres above surface level, under warm, windy and low‐humidity conditions. Although the moths followed a trajectory too low to be tracked by a nearby weather radar, potential bioscatter reflectivities were detected at higher altitudes, suggesting that the moths that landed in Sally's Cove could have been part of a larger dispersal event. Immigrant moths from Anticosti Island may have led to an increase in SBW population levels observed around Sally's Cove in the fall of 2018 and ultimately to the development of a large‐scale outbreak on Newfoundland's west coast. This study provides a better understanding of SBW long‐range migratory flights, which can be used to anticipate and reduce the risks and impacts of future outbreaks.