Tree-ring evidence of larch sawfly outbreaks in western Labrador, Canada

Abstract

As many insect outbreak reconstructions are typically based on targeted single-site sampling, researchers have often been limited in their ability to draw conclusions about regional trends as opposed to local trends in the data. The results of this paper demonstrate the value of a systematic sampling design when studying spatio-temporal processes that can vary greatly within large continuous areas of forest. Many single-site research programs have been conducted to reconstruct the history of larch sawfly ( Pristiphora erichsonii Htg.) outbreaks in the eastern boreal region of North America. However, no such research has yet been conducted in the region of Labrador. In an attempt to illustrate the strength of a systematic gridded sampling protocol over a single-site study, we sampled a 12-site grid in western Labrador. Dominant and codominant species were sampled at each grid point, resulting in 24 master chronologies. Six eastern larch ( Larix laricina (Du Roi) K. Koch) chronologies (host) and a regional black spruce ( Picea mariana (Mill.) Britton, Sterns, Poggenb.) chronology (nonhost) were used to establish a host–nonhost analysis of past sawfly outbreaks on a regional scale. Both regional and localized larch sawfly outbreaks were identified, but in general, larch sawfly outbreaks in western Labrador appeared to be spatially synchronous and regional in scale.

Population studies of tree-defoliating insects in Canada: a century in review

“…The first recorded outbreak in North America occurred along the eastern seaboard in 1880 and then appeared to spread north and west -this outbreak was speculated to represent the unintentional introduction of larch sawfly to North America from Europe (Fyles 1892;Hewitt 1912;Ives and Muldrew 1984). However, evidence from tree-ring growth patterns in tamarack from Québec and Labrador indicates that larch sawfly outbreaks have a long history in Canada that far predates the 1880s (Jardon et al 1994;Nishimura and Laroque 2010). Although the periodicity of outbreaks is highly variable (i.e., between 14 and 77 years), there is some observational evidence of regional synchronicity in outbreaks (Table 2).…”

“…Time-series studies of larch sawfly have focussed largely on establishing that larch sawfly is a native defoliator to Canada (Ives and Muldrew 1984; Nishimura and Laroque 2010). The first recorded outbreak in North America occurred along the eastern seaboard in 1880 and then appeared to spread north and west – this outbreak was speculated to represent the unintentional introduction of larch sawfly to North America from Europe (Fyles 1892; Hewitt 1912; Ives and Muldrew 1984).…”

A history of biological control in Canadian forests, 1882–2014

“…In a final wrinkle, Wong (1974) showed that the larch sawfly was a Holarctic species and likely had been present in North America since the Permian (250 mya). Early dendrochronological studies from across North America (reviewed by Ives and Muldrew 1984), and recent work from northern Canada by Nishimura and Laroque (2010), both suggest that the larch sawfly is native to North America, although its actual distribution remains uncertain. If Wong’s hypothesis is correct, then the non-native agents introduced by Hewitt during the early 1900s actually formed a “new association” that initially suppressed the native larch sawfly (Hewitt 1912; Glen 1956), but this was then disrupted by the inadvertent contamination and release of a resistant strain of European sawfly and its hyperparasitoids.…”

Analysis of fisheye photography for monitoring canopy structure during larch sawfly outbreak

“…Large populations of this sawfly species can cause substantial damage to larch forests. Larch sawfly emerge from May to July, depositing their eggs on newly developed larch shoots on which they feed for several weeks [5] [6]. Larvae drop to the ground in July and August, spin cocoons, and overwinter before reaching adulthood the following May or June.…”