Effects of simulated climate warming and population source on synchrony of forest tent caterpillar (Malacosoma disstria Hübner) egg hatch and host leaf phenology

Mean annual temperatures in the southern boreal forest of northern Minnesota have risen ~1.5° C since 1940, and are expected to increase an additional 3-11° C by 2100.  How these changes will affect phenological synchrony between herbivores and their host plants is poorly understood. The issue is further complicated by a spatiotemporal component, namely the expectation that insects will respond more readily than trees by migrating as warming gradually proceeds.  We are investigating the interaction of population source and elevated temperatures on egg eclosion by an outbreak folivore species, the forest tent caterpillar (Malacosoma disstria HŸbner), in relation to budbreak and leaf development of two of its major hosts, trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera).  We collected egg masses from four populations across a latitudinal gradient, and subjected them to two overwintering regimes (northern MN, southern WI).  In spring, egg bands from the different sources and overwintering treatments were distributed across three temperature regimes at the "B4Warmed Project" in northern Minnesota: ambient, +1.8°C, and +3.6°C. We quantified egg hatch and plant phenological development.  Egg hatch timing varied among population source, overwintering location, and spring temperature regime. Plant phenological development was earlier in paper birch.  Among both species, we observed earlier development with warmer spring temperature regime.  These findings will provide useful information for managing forest insect defoliators under a warming climate.