Periodicity and synchrony of pine processionary moth outbreaks in France

Although many forest Lepidoptera are known to exhibit cyclic outbreaks in temperate forests, this has never been formally demonstrated for the pine processionary moth (Thaumetopoea pityocampa), the main insect defoliator of southern Europe. Yet, the demonstration of periodicity in the population dynamics of forest defoliators is of great interest for developing predictive risk models. We took advantage of 32 years time series recorded on permanent plots throughout France to test for the cyclicity of T. pityocampa outbreaks, estimate the length of cyclic periods and investigate synchrony between regions. Spectral analysis revealed that a large majority of regions and clusters of monitoring plots show significantly periodic outbreaks with a return period of seven to nine years. Outbreaks were not synchronous across the whole country but in neighbouring regions. Several factors such as low host tree quality following defoliation, impact of natural enemies and prolonged diapause might drive the cyclicity of T. pityocampa outbreaks while the Moran effect, here the role of low temperatures, is likely to explain synchrony. (C) 2015 Elsevier B.V. All rights reserved.