INFLUENCE OF SOIL HYDRIC PARAMETERS ON THE WINTER COLD-HARDINESS OF ABURROWING BEETLE, LEPTINOTARSA-DECEMLINEATA (SAY)

This investigation examined the influence of soil moisture and associa ted parameters on the cold hardiness of the Colorado potato beetle (Le ptinotarsa decemlineata Say), a temperate-zone species that overwinter s in terrestrial burrows. The body mass and water content of adult bee tles kept in sand at 4 degrees C varied over a 16-week period of diapa use according to the substratum's moisture content. Changes in body wa ter content, in turn, influenced the crystallization temperature (rang e -3.3 to -18.4 degrees C; n = 417), indicating that environmental moi sture indirectly determined supercooling capacity, a measure of physio logical cold hardiness. Beetles held in dry sand readily tolerated a 2 4-h exposure to temperatures ranging from 0 degrees to -5 degrees C, b ut 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 in oculative freezing. Mortality of beetles exposed to -5 degrees C for 2 4 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 i nsects.