Many agricultural pests, such as the Colorado potato beetle (CPB, Leptinotarsu decemlineata), overwinter underground, but not all pests that burrow will survive the winter.
Many agricultural pests, such as the Colorado potato beetle (CPB, Leptinotarsu decemlineata), overwinter underground, but not all pests that burrow will survive the winter. Two factors that influence the number of CPB that survive the winter are the depth of the burrow and winter soil temperatures. If only a small percentage of CPB survive, pest pressure on solanaceous crops (especially potatoes and eggplants) is reduced. If a large percentage of CPB survive, pressure on these crops will be greater, requiring producers to control the population using mechanical or chemical approaches. CPB represents the most important insect defoliator of potatoes throughout the Northern Hemisphere (Alyokhin et al. 2008). Therefore, it is a good species to examine in the context of climate change and changing winter temperatures.
Though CBP originated in subtropical regions (i.e., central Mexico), it has adapted to survive and thrive in various environments, including the Northeastern United States. Our research group studied overwintering experiments with two CPB populations. One population was subtropical (from Central Mexico) and the other was established in the more temperate region (Vermont). This research helped us to better understand what factors contribute to the overwintering survivorship of CPB within temperate climates (Izzo et al. 2014a, 2014b), such as the Northeastern United States.
According to our findings, overwintering success is linked both to the CPB’s evolved behavior (e.g., when they burrow, burrowing depth) and seasonal environmental factors (e.g., soil temperatures, plant host quality). CPB populations in temperate climates burrow deeper into the soil to better survive colder winter temperatures in these regions. Depending upon the depth of the frost line within the soil (which is related to the air temperature), beetle survivorship may vary significantly over seasons. Some beetles may not reach “safe” overwintering sites during cold years, while milder seasons may allow overwintering beetles to more easily survive.
These findings are especially relevant under current climate change scenarios. Intuitively, warmer soil temperatures and shallower frost lines within Northeast landscapes should increase overwintering survivorship of CBP, and therefore increase pest pressure on solanaceous crops. However, fluctuating soils temperature may actually reduce overwintering success by disrupting CPB life cycles. Beetles emerging early or burrowing late due to prematurely warming soil temperatures may ultimately die when temperatures drop. Nevertheless, it is evident from our study that changing soil temperatures will exhibit a profound effect on the population dynamics of temperate CPB populations.
By Victor Izzo, Lecturer, University of Vermont Agroecology and Rural Livelihoods Group, Department of Plant and Soil Sciences