Drought-induced positive feedback in xylophagous insects: Easier invasion of Scots pine leading to greater investment in immunity of emerging individuals

Indrikis Krams, Janina Daukšte, Inese Kivleniece, Guntis Brumelis, Raimonds Cibuļskis, Mikus aboliņš-abols, Markus J. Rantala, Pranas Mierauskas, Tatjana Krama

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We studied the infestation rate of Scots pine Pinus sylvestris by xylophagous insects in relation to distance from forest lakes in eastern Latvia, northern Europe. In summers of 2008 and 2009, we felled 72 pines of approximately 65. years age. Sections of the logs were incubated in insect emergence traps. The trees located near lakes were significantly less infested by xylophagous insects than those sampled at greater distances from the lakes. We also tested the ability of Tomicus piniperda, the most abundant species of xylophagous insects in our samples, to resist the entomopathogenic fungus Beauveria bassiana. The results show that beetles captured near lakes were more susceptible to the fungal infection than individuals sampled away from forest lakes, indicating that the beetles far from lakes afforded to invest more in immunity during the larval phase. During the warmest days in summer the mean maximum ambient temperature was 2.32 °C lower near lakes than away from lakes. Since increased temperatures not only trigger drought stress, but may potentially also cause temperature-sensitive mortality of conifers, a warmer microclimate may lower resistance of pine trees to attacks of xylophagous beetles. In weakened trees, insects can invade more easily resulting in increased investment in immunity in bark- and wood-boring insects. This is the first demonstration of drought-induced positive feedback in xylophagous insects infesting Scots pine. Since bark beetles are common pests of conifers, our results may be important in forest pest management.

Original languageEnglish
Pages (from-to)147-152
Number of pages6
JournalForest Ecology and Management
Publication statusPublished - Apr 15 2012



  • Bark beetles
  • Drought stress
  • Infestation rates
  • Insect immunity
  • Scots pine

ASJC Scopus subject areas

  • Forestry
  • Management, Monitoring, Policy and Law
  • Nature and Landscape Conservation

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