Gene expression analysis of overwintering mountain pine beetle larvae suggests multiple systems involved in overwintering stress, cold hardiness, and preparation for spring development.

Jeanne A Robert,Luke J Spooner,Tiffany Bonnett,Jordie Fraser,Dezene P.W Huber,Macaire M.S Yuen,Caitlin Pitt,Christopher I Keeling,Jörg Bohlmann

doi:10.7717/peerj.2109

Abstract

Cold-induced mortality has historically been a key aspect of mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), population control, but little is known about the molecular basis for cold tolerance in this insect. We used RNA-seq analysis to monitor gene expression patterns of mountain pine beetle larvae at four time points during their overwintering period—early-autumn, late-autumn, early-spring, and late-spring. Changing transcript profiles over the winter indicates a multipronged physiological response from larvae that is broadly characterized by gene transcripts involved in insect immune responses and detoxification during the autumn. In the spring, although transcripts associated with developmental process are present, there was no particular biological process dominating the transcriptome.

Highlights

Changing climate and large contiguous stands of susceptible lodgepole pine (Pinus contorta Douglas) have resulted in a large mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae) outbreak in British Columbia and other parts of western North America (Raffa et al, 2008)
The large scale of this outbreak in British Columbia, in combination with the expansion of mountain pine beetle into previously unaffected areas of jack pine, Pinus bankisana Lamb, forests in Alberta (Cullingham et al, 2011), have caused substantial economic losses in British Columbia (Schneider et al, 2010) and continue to have massive ecological effects on the landscape
How to cite this article Robert et al (2016), Gene expression analysis of overwintering mountain pine beetle larvae suggests multiple systems involved in overwintering stress, cold hardiness, and preparation for spring development

Summary

Introduction

Changing climate and large contiguous stands of susceptible lodgepole pine (Pinus contorta Douglas) have resulted in a large mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae) outbreak in British Columbia and other parts of western North America (Raffa et al, 2008). Cold-induced mortality has historically been a key aspect of mountain pine beetle population control. The mountain pine beetle spends much of its typically one-year life cycle as larvae in the phloem tissue of susceptible host trees. While they overwinter under the bark, larvae have had, under typical conditions, to survive winter temperatures below –30 ◦C (Cole, 1981). Cold-induced mortality has historically controlled bark beetle populations in British Columbia and prevented the insects from moving further north or east than their historically known range. Because of the recent move of this insect across the Rocky Mountains and into the jack pine forests of Alberta (Cullingham et al, 2011; Janes et al, 2014), understanding the cold tolerance mechanisms of mountain pine beetle is becoming increasingly important for forest management and the development of predictive models

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Conclusion