Cooling rate affects supercooling points of overwintering spotted lanternfly eggs

Spotted lanternfly, Lycorma delicatula (White) is a planthopper (Hemiptera: Fulgoridae) that is native to China and invasive elsewhere in Asia and North America. The insect feeds on several plants and is an emerging pest of apples, grapes, walnuts, and other hardwoods. Forecasts of the ultimate geographic distribution for L. delicatula in Asia and North America, particularly its northern latitudinal limits, are uncertain because of limited information about the cold tolerance of this insect. Cooling rate can affect supercooling point, the temperature at which bodily fluids begin to freeze and a common reference point for insect cold tolerance studies. This study measures changes in supercooling point of overwintering L. delicatula eggs in response to different cooling rates. Overwintering egg masses were collected from two field locations in Virginia, USA in November and December 2024. Supercooling points of individual eggs were measured with contact thermocouple thermometry at cooling rates of 0.033, 0.5, and 1 °C/min. The distribution of supercooling points changed with different cooling rates and were negatively related to the cooling rate. At a cooling rate of 0.033 °C/min, SCPs ranged from -28.4 to -22.9 °C and, at 1 °C/min, from -29.2 to -24.7 °C. If supercooling points reflect lethal temperatures for L. delicatula, relatively rapid cooling may slightly overestimate the cold tolerance of the insect and inflate the estimated geographic area where overwintering might be successful. Such risk-averse forecasts may be useful for biosecurity efforts.