Anomalous outbreaks of an invasive defoliator and native bark beetle facilitated by warm temperatures, changes in precipitation and interspecific interactions

Samuel F. Ward, Brian H Aukema

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Biotic disturbance agents such as insects can be highly responsive to climatic change and have widespread ecological and economic impacts on forests. Quantifying the responses of introduced and native insects to climate, including how dynamics of one agent may mediate those of another, is important for forecasting disturbance and associated impacts on forest structure and function. We investigated drivers of outbreaks by larch casebearer Coleophora laricella, an invasive defoliator, and eastern larch beetle Dendroctonus simplex, a native, tree-killing bark beetle, on tamarack Larix laricina from 2000 to in Minnesota, USA. We evaluated the utility of temporal, spatial and climatic variables in predicting the presence/absence of outbreaks of each insect in cells of rasterized aerial survey data. The role of defoliation by larch casebearer in outbreaks of eastern larch beetle was also investigated. For both species, the most important predictors of outbreak occurrence were proximity of conspecific outbreaks in space and time. For larch casebearer, outbreak occurrence was positively associated with spring precipitation and warmer growing seasons. Outbreak occurrence of eastern larch beetle was positively associated with warmer and dryer years and was more likely in cells with prior defoliation by larch casebearer. Our results demonstrate that climate can drive large scale outbreaks of introduced and non-native disturbance agents on a single host species, and that interactions at the tree level between such agents may scale up to manifest across large temporal and spatial scales.

Original languageEnglish (US)
Pages (from-to)1068-1078
Number of pages11
Issue number5
StatePublished - May 2019

Bibliographical note

Funding Information:
Acknowledgements – The authors thank Jana Albers, Susan Crocker and Mike Parisio for help with obtaining aerial survey data, Greg Liknes for helpful discussions on climatic data, and two anonymous reviewers for their constructive comments. Funding – This study was funded by USDA Forest Service award 15-DG-1142004-237, the College of Food, Agricultural and Natural Resource Sciences at the Univ. of Minnesota, Minnesota Agricultural Experiment Station project MIN-17-095, and a Univ. of Minnesota Doctoral Dissertation Fellowship to SW. Author contributions – SW conceived the idea, conducted analyses, and wrote the initial draft. BA provided substantial input on analyses and contributed to writing subsequent drafts. Conflicts of interest – None.

Publisher Copyright:
© 2018 The Authors


  • Coleophora
  • Dendroctonus
  • climate change
  • disturbance
  • feeding guilds
  • landscape


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