Journal
ENVIRONMENTAL ENTOMOLOGY
Volume 44, Issue 3, Pages 463-473Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/ee/nvv039
Keywords
bottom-up dynamics; drought stress; host plant and herbivore interaction; long-term study; predictive model tested
Categories
Funding
- U.S. National Science Foundation [DEB-7816152, DEB-8021754, BSR-83144594, BSR-8705302, BSR-8715090, BSR-9020317, DEB-9318188, DEB-9527522]
- NSF [DEB-9906366, DEB-0342750, DEB-1144922]
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The interaction between the arroyo willow, Salix lasiolepis Bentham, and its specialist herbivore, the arroyo willow stem-galling sawfly, Euura lasiolepis Smith (Hymenoptera: Tenthredinidae), was studied for 32 yr in Flagstaff, AZ, emphasizing a mechanistic understanding of insect population dynamics. Long-term weather records were evaluated to provide a climatic context for this study. Previously, predictive models of sawfly dynamics were developed from estimates of sawfly gall density made between 1981 and 2002; one model each for drier and wetter sites. Predictor variables in these models included winter precipitation and the Palmer Drought Severity Index, which impact the willow growth, with strong bottom-up effects on sawflies. We now evaluate original model predictions of sawfly population dynamics using new data (from 2003-2012). Additionally, willow resources were evaluated in 1986 and in 2012, using as criteria clone area, shoot density, and shoot length. The dry site model accounted for 40% of gall population density variation between 2003 and 2012 (69% over the 32 yr), providing strong support for the bottom-up, mechanistic hypothesis that water supply to willow hosts impacts sawfly populations. The current drying trend stressed willow clones: in drier sites, willow resources declined and gall density decreased by 98%. The wet site model accounted for 23% of variation in gall population density between 2003 and 2012 (48% over 30 yr), consistent with less water limitation. Nonetheless, gall populations were reduced by 72%.
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