Modeling Migratory Flight in the Spruce Budworm: Temperature Constraints

Abstract

We describe an individual-based model of spruce budworm moth migration founded on the premise that flight liftoff, altitude, and duration are constrained by the relationships between wing size, body weight, wingbeat frequency, and air temperature. We parameterized this model with observations from moths captured in traps or observed migrating under field conditions. We further documented the effects of prior defoliation on the size and weight (including fecundity) of migrating moths. Our simulations under idealized nocturnal conditions with a stable atmospheric boundary layer suggest that the ability of gravid female moths to migrate is conditional on the progression of egg-laying. The model also predicts that the altitude at which moths migrate varies with the temperature profile in the boundary layer and with time during the evening and night. Model results have implications for the degree to which long-distance dispersal by spruce budworm might influence population dynamics in locations distant from outbreak sources, including how atmospheric phenomena such as wind convergence might influence these processes. To simulate actual migration flights en masse, the proposed model will need to be linked to regional maps of insect populations, a phenology model, and weather model outputs of both large-and small-scale atmospheric conditions.

Density Dependence of Egg Recruitment and Moth Dispersal in Spruce Budworms

“…For example, observed flights of moths from New Brunswick to Newfoundland in Atlantic Canada in the 1980s resulted in damaging outbreaks which lasted only a few years while the source outbreak on the mainland continued for several more years [21]. Our understanding of the ecological conditions determining if, when, and where spruce budworms fly, are relatively well known (e.g., [44][45][46]) but the application of this knowledge to the analysis of population patterns is challenging and has only been accomplished recently [47]. As extensive, annual records of defoliation of outbreaks became available, the research approach on dispersal shifted to empirical, geo-statistical techniques to infer patterns of direction and rate of 'spread' in defoliation that might reveal the ecological structure of moth dispersal [4,10,48].…”

A Conceptual Framework for the Spruce Budworm Early Intervention Strategy: Can Outbreaks be Stopped?

“…L2 monitoring efficiency could be further enhanced in the future through integration with modelling tools to predict moth dispersal patterns via weather forecasting [40] or radar [23], or through defoliation assessment using remote monitoring approaches [41,42].…”

Modeling Migratory Flight in the Spruce Budworm: Circadian Rhythm

“…We consider two factors as determinants of migratory flight of the SBW in this model: Time of day and temperature. Temperature directly affects the flight activity of SBW moths through wingbeat frequency [2]. The literature also suggests that migratory flight may be inhibited when temperature remains above a certain threshold well into the night, and that migratory flight does not occur much after midnight [10].…”

“…(Lepidoptera: Tortricidae) with consideration of near-surface and boundary layer meteorological processes. In a companion paper, we discussed the basic physics of spruce budworm (SBW) flight and developed a mathematical framework with which we can model adult moth migration [2]. The ultimate objective of this work is the development of a simulation model to allow both historical analysis and real-time prediction of SBW population dispersal though moth migration and oviposition.…”