Browsing by Author "Schwartzberg, EG"

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    Effects of winter temperatures, spring degree-day accumulation, and insect population source on phenological synchrony between forest tent caterpillar and host trees
    (Forest Ecology and Management, 2016-02-15) Uelmen, JA; Lindroth, RL; Tobin, PC; Reich, PB; Schwartzberg, EG; Raffa, KF
    Global 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.
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    Supercooling points of diapausing forest tent caterpillar (Lepidoptera: Lasiocampidae) eggs
    (Canadian Entomologist, 2016-10-01) Uelmen, JA; Duman, JG; Lindroth, RL; Schwartzberg, EG; Raffa, KF
    Forest tent caterpillar (Malacosoma disstria Hübner; Lepidoptera: Lasiocampidae) is a widely distributed defoliator that undergoes intermittent outbreaks. It overwinters as pharate larvae within egg bands, is univoltine, and experiences low winter temperatures in its northern range. Little is known about how low temperatures affect winter survival and cold tolerances, their cold tolerance strategy, or how cold tolerances may vary over time and among populations. We evaluated supercooling points (SCPs) from four populations of M. disstria eggs collected along a 552 km latitudinal gradient from southern Wisconsin to northern Minnesota, United States of America. To test for potential effects of winter environment, we also administered three overwintering regimes (Madison, Wisconsin; Cloquet, Minnesota; Ely, Minnesota). Supercooling points were recorded in November, February, and March of 2011-2012. Supercooling points varied with maternal source (egg band), time of winter season, population source, and overwintering treatment. Means ranged from -26.8 °C (±0.5 °C) to -40.3 °C (±0.3 °C), accordingly. In a separate laboratory experiment, 89% of pharate larvae held at -20 °C (18.3 °C above coolest mean SCP) survived, but none held at -45 °C (6.7 °C below lowest mean SCP) survived. This relatively high degree of cold tolerance in its overwintering stage, due to freeze avoidance, may partially explain survival patterns and limits of overwintering M. disstria in northern populations.