Phase-dependent outbreak dynamics of geometrid moth linked to host plant phenology

Abstract

Climatically driven Moran effects have often been invoked as the most likely cause of regionally synchronized outbreaks of insect herbivores without identifying the exact mechanism. However, the degree of match between host plant and larval phenology is crucial for the growth and survival of many springfeeding pest insects, suggesting that a phenological match/mismatch-driven Moran effect may act as a synchronizing agent.We analyse the phase-dependent spatial dynamics of defoliation caused by cyclically outbreaking geometrid moths in northern boreal birch forest in Fennoscandia through the most recent massive outbreak (2000 -2008). We use satellite-derived time series of the prevalence of moth defoliation and the onset of the growing season for the entire region to investigate the link between the patterns of defoliation and outbreak spread. In addition, we examine whether a phase-dependent coherence in the pattern of spatial synchrony exists between defoliation and onset of the growing season, in order to evaluate if the degree of matching phenology between the moth and their host plant could be the mechanism behind a Moran effect.The strength of regional spatial synchrony in defoliation and the pattern of defoliation spread were both highly phase-dependent. The incipient phase of the outbreak was characterized by high regional synchrony in defoliation and long spread distances, compared with the epidemic and crash phase. Defoliation spread was best described using a two-scale stratified spread model, suggesting that defoliation spread is governed by two processes operating at different spatial scale. The pattern of phase-dependent spatial synchrony was coherent in both defoliation and onset of the growing season. This suggests that the timing of spring phenology plays a role in the large-scale synchronization of birch forest moth outbreaks.

Phenological asynchrony between herbivorous insects and their hosts: signal of climate change or pre-existing adaptive strategy?

“…The potential importance of climate change to climate-sensitive endangered species, such as the bay checkerspot is self-evident. In contrast, the winter moth is far from being an endangered species: it is a forest pest with frequent outbreaks (Cuming 1961;Hagen et al 2007;Jepsen et al 2009). However, as a typically abundant species, it is such an important link in the food chain that a decline in its abundance owing to reduced synchrony with oak would affect not only the moths but also the birds that depend on them to raise their chicks.…”

Variation in Captures of Adult Winter Moths (Operophtera brumata) in Coastal Maine Over Two Years

“…czereapanovii) forests of that region in synchrony with, but lagging 2-3 years behind, those of the well-studied geometrid autumnal moth, Epirrita autumnata (Tenow 1972, Tenow et al 2007). Jepsen et al (2009) used satellite data of leaf out and defoliation to show that favorable synchrony of winter moth hatch with bud-break fueled the synchronous outbreak of winter moths during the increase phase of the population cycle. The synchrony was reduced during the peak and declining phases of the outbreak.…”

Discovery of continental-scale travelling waves and lagged synchrony in geometrid moth outbreaks prompt a re-evaluation of mountain birch/geometrid studies

“…The results and conclusions in five of them are relevant in the present context. These papers are Ims et al (2004) 11 , Hagen et al (2008) 12 , Jepsen et al (2009a) 13 , Jepsen et al (2009b) 14 and Jepsen et al (2011) 15 . The papers are interconnected, and to a large extent written by the same authors, and are therefore considered together.…”

“… a ) Map of northern Fennoscandia where defoliations of birch forests during outbreaks of E. autumnata and O. brumata in 2000–2008 were mapped from satellite imagery (Jepsen et al 2009a 13 ; 2009b 14 ). Framed area marks the area for intensive studies of O. brumata occurrence in 1999–2009 (Ims et al 2004 11 ; Hagen et al 2008 12 ; Jepsen et al 2011 15 ).…”