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Oecologia

, Volume 150, Issue 3, pp 519–526 | Cite as

Effects of group size and pine defence chemicals on Diprionid sawfly survival against ant predation

  • Lindstedt CaritaEmail author
  • Mappes Johanna
  • Päivinen Jussi
  • Varama Martti
Behavioral Ecology

Abstract

The defence chemicals and behavioural adaptations (gregariousness and active defensive behaviour) of pine sawfly larvae may be effective against ant predation. However, previous studies have tested their defences against very few species of ants, and few experiments have explored ant predation in nature. We studied how larval group size (groups of 5 and 20 in Neodiprion sertifer and 10, 20 and 40 in Diprion pini) and variation in levels of defence chemicals in the host tree (Scots pine, Pinus sylvestris) affect the survival of sawfly larvae. Food preference experiments showed that ants do eat sawfly larvae, although they are not their most preferred food item. According to our results, ant predation significantly increases the mortality rate of sawfly larvae. Larval mortality was minor on pine tree branches where ant traffic was excluded. We also found that a high resin acid concentration in the host tree significantly decreased the mortality of D. pini larvae when ants were present. However, there was no such relationship between the chemical concentrations of the host tree and larval mortality for N. sertifer. Surprisingly, grouping did not help sawfly larvae against ant predation. Mortality risk was the same for all group sizes. The results of the study seemingly contradict previous understanding of the effectiveness of defence mechanisms of pine sawfly against ant predation, and suggest that ants (Formica exsecta in particular) are effective predators of sawfly larvae.

Keywords

Antipredator defence Resin acid Gregariousness Formica Diprionidae 

Notes

Acknowledgments

We wish to thank all partners in this cooperative study: Risto Jalkanen of the Finnish Forest Research Institute, Päivi Lyytikäinen-Saarenmaa (Univ. of Helsinki), Bert De Somviele (Univ. of Joensuu), UPM Kymmene and Stora Enso. We are grateful to Jouni Sorvari for help in determining ant species. We also thank Rauno Alatalo, Leena Lindström, Eira Ihalainen and members of the “round table” discussion of the department who commented on an earlier version of the manuscript. The study was done with the financial support of the Finnish Entomological Society, Societas Biologica Fennica Vanamo, Metsämiesten säätiö and the Academy of Finland. Maxine Iversen kindly corrected the language. These experiments comply with the current laws of Finland.

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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Lindstedt Carita
    • 1
    Email author
  • Mappes Johanna
    • 1
  • Päivinen Jussi
    • 2
  • Varama Martti
    • 3
  1. 1.Department of Biological and Environmental ScienceUniversity of JyväskyläJyväskyläFinland
  2. 2.Natural Heritage Services of MetsähallitusJyväskyläFinland
  3. 3.Finnish Forest Research InstituteVantaaFinland

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