Influence of soil hydric parameters on the winter cold hardiness of a burrowing beetle, Leptinotarsa decemlineata (Say)

This investigation examined the influence of soil moisture and associated parameters on the cold hardiness of the Colorado potato beetle (Leptinotarsa decemlineata Say), a temperate-zone species that overwinters in terrestrial burrows. The body mass and water content of adult beetles kept in sand at 4 degrees C varied over a 16-week period of diapause according to the substratum's moisture content. Changes in body water content, in turn, influenced the crystallization temperature (range -3.3 to -18.4 degrees C; n = 417), indicating that environmental moisture indirectly determined supercooling capacity, a measure of physiological cold hardiness. Beetles held in dry sand readily tolerated a 24-h exposure to temperatures ranging from 0 degrees to -5 degrees C, but those chilled in sand containing as little as 1.7% water (dry mass) had elevated mortality. Thus burrowing in dry soils not only promotes supercooling via its effect on water balance, but may also inhibit inoculative freezing. Mortality of beetles exposed to -5 degrees C for 24 h was lower in substrates composed of sand, clay and/or peat (36-52%) than in pure silica sand (78%) having an identical water content (17.0% dry mass). In addition to moisture, the texture, structure, water potential, and other physico-chemical attributes of soil may strongly influence the cold hardiness and overwintering survival of burrowing insects.