Overwintering physiology and microhabitat use of Phyllocnistis populiella (Lepidoptera: Gracilliariidae) in interior Alaska.

We investigated the overwintering physiology and behavior of Phyllocnistis populiella Chambers, the aspen leaf miner, which has caused severe and widespread damage to aspen in Alaska over the past 10 yr. Active P. populiella moths caught in spring and summer supercooled to an average temperature of -16°C, whereas dormant moths excavated from hibernacula in the leaf litter during fall and winter supercooled to an average of -32°C. None of the moths survived freezing in the laboratory. Counts of overwintering moths in leaf litter across microhabitats in interior Alaska demonstrated that moths occurred at significantly higher density beneath white spruce trees than beneath the aspen host, several other hardwood species, or in open areas among trees. During winter, the temperature 1-2 cm below the surface of the leaf litter beneath white spruce trees was on average 7-9°C colder than beneath aspen trees, and we estimate that during at least one period of the winter the temperature under some white spruce trees may have been cold enough to cause mortality. However, the leaf litter under white spruce trees was significantly drier than the litter from other microhabitats, which may assist P. populiella moths to avoid inoculative freezing because of physical contact with ice. We conclude that in interior Alaska, P. populiella overwinter in a supercooled state within leaf litter mainly under nonhost trees, and may prefer relatively dry microhabitats over moister ones at the expense of lower environmental temperature.