Perrault, K. | Search bioRxiv

bioRxiv2025

A novel integrated framework to identify and characterize regional-scale pest insect dispersal

Forest pest insects cause major socio-economic impacts, global losses of millions of dollars, and ecosystem changes. A key challenge for their management is tracing regional dispersal events critical to outbreak dynamics. We developed an integrated tracing framework for pest insects by combining isotope geolocation, ecological data, and atmospheric modeling, and applied this framework to the eastern spruce budworm moth (Choristoneura fumiferana), the most severe defoliator of the North American boreal forest, to trace outbreak dispersal events. We first generated a North American model of bioavailable sulfur isotope ({delta}34S) variation in space (isoscape), which predominantly varied in response to oceanic sulfate deposition, and then calibrated it to spruce budworm tissues of known origin. We used an automated trap network with high temporal resolution to collect samples and identify potential immigration events of eastern spruce budworm to Nova Scotia, Canada. We traced the natal origin of these immigrants by integrating high-probability regions derived from{delta} 34S probabilistic assignments and HYSPLIT atmospheric dispersal models. Since high larval density is a strong predictor of budworm defoliation and emigration, HYSPLIT atmospheric dispersal models, which integrated spruce budworm behavioral constraints (e.g., flight velocity, altitude, and temperature thresholds), were started from defoliated areas to narrow-down the area of natal origin and estimate the migration route. We find that this integrated framework allows to narrow down the region of pest origins, restricting it to a few possible locations and demonstrating long-distance dispersal of spruce budworm across [~]400Km over the Gulf of St. Lawrence. Our framework demonstrates the utility of{delta} 34S geolocation in insect tracing, and that combining isotopic data with ecological indicators and atmospheric modeling offers an unprecedented resolution in understanding insect dispersal ecology. The approach is transferable to trace other migratory insect species to address conservation, agriculture, and bio-surveillance needs in the context of global environmental change.

ecology↗

bioRxiv2022

Characterizing Eastern spruce budworm's large-scale dispersal events through flight behavior and stable isotope analyses

Eastern spruce budworm moth (Choristoneura fumiferana (Clem.)) mass outbreaks have widespread economic and ecological consequences. A key explanation for the large-scale spread and synchronization of these outbreaks is the long-distance dispersal (up to 450km) of moths from hotspots (high-density populations) to lower-density areas. These events have proved difficult to monitor because dispersal flights occur only a few times a year, have no consistent routes, and commonly used tracking methods (e.g., population genetics, mark-recapture, radio telemetry) are inadequate for this system. Distinguishing between local and immigrant individuals is a crucial step in identifying the physical and ecological drivers of moth dispersal. Here we test whether isotopes of hydrogen (i.e., delta notation:{delta} 2H) and strontium (i.e., strontium isotope ratios: 87Sr/86Sr), known to independently vary in space in a predictable manner, can be used to distinguish between local and immigrant adult spruce budworm moths. We used an automated pheromone trap system to collect individuals at six different sites in eastern Canada within and outside the current outbreak area of budworm moths. We first use moth flight behaviour and time of capture, currently the best available tool, to determine putative local vs. immigrant status, and then evaluate whether individual 87Sr/86Sr and{delta} 2H differ between putative classes. At all sites, we detect immigrant individuals that differ significantly from putative locals. Saliently, sites where putative locals were sampled before the occurrence of potential immigration events (~10 days) showed the strongest differences between immigrant individuals and the locals 87Sr/86Sr and{delta} 2H values. Sites where the collection of putative locals was close in time (hours) or following an immigration event had a less-clear distinction between putative immigrants and locals, and showed signs of mixing between these two groups. We speculate that recent immigration could have led to the misclassification of immigrants as putative locals. 87Sr/86Sr and{delta} 2H data generally support the adequacy of current approaches using capture-time to detect immigration events, and provide enhanced resolution to distinguish between local and immigrant individuals. We discuss the broader implication of adding isotopes to the toolkit to monitor spruce budworm dispersal and suggest next steps in implementing these tools.

ecology↗