Comparative ecology of conifer-feeding spruce budworms (Lepidoptera: Tortricidae)

Abstract

Abstract-The comparative ecology of conifer-feeding budworms in the genus Choristoneura Lederer (Lepidoptera: Tortricidae) in Canada is reviewed with emphasis on publications since 1980. Systematics and life history are updated and historical outbreak patterns and their current interpretation summarised. Recent evidence is analysed in the context of ecological interactions among three trophic levels; host plant, budworm herbivore, and natural enemies. The influence of weather and climate are viewed as modulating factors. The population behaviour of budworms is interpreted as the result of tri-trophic interactions that vary at different scales. The result of these multi-scale interactions is that despite shared phylogenetic constraints and common adaptations, different budworm species display different population behaviour because of specific ecological relationships with their respective hosts and natural enemies.

An alternative hypothesis explains outbreaks of conifer‐feeding budworms of the genus Choristoneura (Lepidoptera: Tortricidae) in Canada

“…The larvae of all species of conifer‐feeding budworms when they start to feed are flush feeders on buds and new growth, but if they mine old needles before bud flush they first become senescence‐feeders and later flush feeders: they become “double‐dippers” (White, ). Having hibernated mostly in the crown of the trees where the eggs were laid, the following spring they leave their hibernacula and commence feeding on old needles (McGugan, ), sometimes for weeks (Nealis, ), mining them selectively to eat only the mesophyll that contains the highest level of nitrogen, thus providing them with “… sustenance in the midst of privation.” (Tier & Mattson, ), but this sustenance may still not be sufficient to enable more than a few of these larvae to survive, especially when they emerged weeks before bud‐burst. And just how important the ability to access these old needles can be to the success of these neonate larvae is illustrated by their failure to survive on host species whose needles they are unable to feed on (Fuentealba, Sagne, Pureswaran, Bauce, & Despland, ).…”

“…Yet between outbreaks, for periods of many years, their endemic populations remain so small and sparse as to be virtually undetectable even by the most diligent search. Two recent reviews (Nealis, ; Pureswaran, Johns, Heard, & Quiring, ; and references in both) provide updates and overviews of the research into the ecology of these outbreaking species of budworms in Canada. Pureswaran et al.…”

“…Pureswaran et al. () focus on outbreaks of the eastern spruce budworm, Choristoneura fumiferana (Clemens) in New Brunswick, identifying unresolved questions and explanations while Nealis () covers more recent empirical research on all the major species and emphasizes emerging insights into the understanding of the interaction of bottom‐up and top‐down processes in generating outbreaks.…”

“…More recent research has partially shifted the focus of the debate to the role that defoliation of trees during an outbreak might have in the decline of populations by diminishing the survival of neonates, and the role that moths immigrating from high populations might have in generating the start of outbreaks (Nealis, ). Nevertheless, the consensus of research to date is that while these may be contributing factors, control by natural enemies is the primary agent in both the generation and decline of outbreaks and in keeping populations at low levels between outbreaks.…”

Insects affecting regenerating conifers in Canada: natural history and management

“…The outbreak reached its peak in terms of area in 2008 when over 30 779 ha of Douglas-fir stands were attacked. It was, however, in 2007 when the impact of this outbreak was greater because severe defoliation was observed in over 16 201 ha in Porcupine Hills (Environment and Sustainable Resource Development Alberta 2008, 2013.…”