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• Gypsy Moths

Climate related factors which might influence gypsy moth distributions:

• Air Temperature predicted to increase
• Tree Species Distribution related to air temperature and precipitation
• Tree/Leaf Growth related to air temperature and precipitation
• Leaf Nitrogen Concentration related to atmospheric CO2 concentrations, predicted to decrease

Gypsy moths (and other insects) are ectothermic, or cold-blooded, which makes them particularly sensitive to climatic changes (e.g. Logan et al. 2003, Vanhaven et al. 2007), because it is hard for them to compensate for an unfavorable climate. Gypsy moths require a climate warm enough for the adults to emerge, have time to mate, lay eggs and for the eggs to have some development prior to the onset of winter. At the same time, the winter chilling temperatures are also important for egg development. (See Régnière and Negalis 2002) Climate change is predicted to result in northern (Vanhanen et al. 2007) and western (Logan 2003) shifts in Gypsy moth change. Gypsy moth presence has declined in Virginia, most likely due to management actions; however changes in climatic conditions may reduce the suitable habitat in Virginia further over time. Decline of gypsy moths in Virginia also may be due to previous infestations that significantly reduced the oak population.

{{youtube:large|MX0TQ8Oeyps,Gypsy Moth Defoliation 1984-2009}}

Gypsy Moth Defoliation 1984-2009 (Video Animation) - Note: the year is listed in the upper left corner of the map

Gypsy moth health and population size is affected by the health and distribution of the trees they live on. They tend to be found in oak-dominated forests and although they will eat the leaves of a variety of hardwood tree species, oaks are their preferred food source (USDA Forest Service 1990). Climate conditions that adversely affect tree and/or leaf growth also adversely affect gypsy moth populations. Drought conditions decrease Black Poplar net assimilations rates, photosynthesis and growth, resulting in a concomitant decrease in gypsy moth larvae (Hale et al. 2005). Under increasing CO2, leaf nitrogen content is expect to decrease, this has been found to strongly affect gypsy moth survival (Lindroth et al. 1997).

The impact of gypsy moths on forests is not limited to the defoliation of a single tree or tree species, and climatic changes may interact with these impacts in unexpected ways. High temperatures tend to increase the potential for tree defoliation by decreasing gypsy moth long-term development rates and increasing short-term growth and consumption rates (Lindroth et al. 1997). Although decreased leaf nitrogen results in reduced survival, sublethal levels result in increased leaf consumption (Lindroth et al. 1997), which can increase the impact on the tree population. In addition, drought-stressed trees are more susceptible to gypsy moth defoliation (Fosbroke and Hicks 1989). Gypsy moth preference for hardwood tree species can lead to changes in forest composition as hardwood tree species are replaced by more softwood species (Hix et al. 1991). This, in turn, can alter food chains and change habitat types as large, hard mast producing species are replaced by smaller, berry producing species.

Other potential relationships which could be affected by climate include: