Browsing by Subject "plant-insect interactions"
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Item Effects of winter temperatures, spring degree-day accumulation, and insect population source on phenological synchrony between forest tent caterpillar and(Elsevier, 2016) Uelmen, Johnny A.; Lindroth, Richard L; Tobin, Patrick C.; Reich, Peter B; Schwartzberg, Ezra G; Raffa, Kenneth FGlobal climate change has the potential to dramatically alter multiple ecosystem processes, including herbivory. The development rates of both plants and insects are highly sensitive to temperature. Although considerable work has examined the effects of temperature on spring phenologies of plants and insects individually, few studies have examined how anticipated warming will influence their phenological synchrony. We applied elevated temperatures of 1.7 and 3.4 °C in a controlled chamberless outdoor experiment in northeastern Minnesota, USA to examine the relative responses in onset of egg eclosion by forest tent caterpillar (Malacosoma disstria Hübner) and budbreak of two of its major host trees (trembling aspen, Populus tremuloides Michaux, and paper birch, Betula papyrifera Marshall). We superimposed four insect population sources and two overwintering regimes onto these treatments, and computed degree-day models. Timing of egg hatch varied among population source, overwintering location, and spring temperature regime. As expected, the development rates of plants and insects advanced under warmer conditions relative to ambient controls. However, budbreak advanced more than egg hatch. The degree of phenological synchrony between M. disstria and each host plant was differentially altered in response to warming. The interval by which birch budbreak preceded egg hatch nearly doubled from ambient to +1.7 °C. In the case of aspen, the sequence changed from egg hatch preceding, to following, budbreak at +3.4 °C. Additionally, under temperature regimes simulating future conditions, some insect populations currently south of our study sites became more synchronous with the manipulated hosts than did currently coexisting insect populations. These findings reveal how climate warming can alter insect-host plant interactions, through changes in phenological synchrony, possibly driving host shifts among tree species and genotypes. They also suggest how herbivore variability, both among populations and within individual egg masses, may provide opportunities for adaptation, especially in species that are highly mobile and polyphagous.Item Long-term effects of defoliation on red pine suitability to insects feeding on diverse plant tissues(Ecological Society of America, 1998) Raffa, Kenneth F; Krause, Steven C; Reich, Peter BEvidence that defoliation can induce long-term responses in perennial plants that can regulate insect population dynamics is based largely on studies using deciduous trees and folivores, particularly Lepidoptera. Studies with evergreen trees, and with insects feeding on other plant parts, have yielded more variable results. This study examined the effects over several seasons of controlled defoliation on the suitability of an evergreen conifer, red pine (Pinus resinosa) to insects and pathogens that exploit foliage, stem phloem, and root tissue. Test insects included a folivorous sawfly (Hymenoptera) and two species of stem- and root-colonizing beetles (Coleoptera). Each of these species undergoes periodic population irruptions. Controlled defoliations were administered to 10-yr-old trees at levels that mimic naturally occurring sawfly outbreaks. Additional studies were conducted on seedlings in a glasshouse. Foliar suitability to the redheaded pine sawfly (Neodiprion lecontei) varied in a nonlinear fashion with defoliation intensity one year after treatment. However, not all parameters of sawfly success were equally affected. Female cocoon mass was related to foliar concentrations of nutrients, but not monoterpenes or diterpene acids. Suitability to the stem boring pine engraver (Ips pini) increased 2 yr after defoliation. Moderate defoliation reduced stem resin flow rate by 50% and increased stem phloem colonization rate by the beetle’s mutualistic fungus, Ophiostoma ips. Defoliation also affected host suitability to adult pales weevils, Hylobius pales. Weevil feeding increased 1 yr after defoliation, but this response dissipated 2 yr after treatment. The observation that intermediate defoliation stress can either decrease or increase foliar suitability in an evergreen conifer, depending on intensity, is consistent with elements of both the plant stress and carbon:nutrient balance hypotheses. Moreover, host responses to a single stress agent may significantly and differentially influence the population dynamics of insects and pathogens that exploit different plant tissues. Implications of these results for plant stress and carbon:nutrient theories, plant-herbivore interactions, and chronic forest declines are discussed.