Cold tolerance strategy and lower temperature thresholds of Lycorma delicatula egg masses

Abstract Spotted lanternfly (Lycorma delicatula, Hemiptera: Fulgoridae) is a planthopper native to China and southeastern Asia invasive in North America. To inform risk assessment of northward spread, we determined cold tolerance strategy and lower lethal limits of overwintering eggs. We used field-collected egg masses from Pennsylvania, USA, and treated them with short (1 or 12 h) and long (10 or 15 days) low temperature exposures (0 °C to -25 °C). We assessed hatch rate to measure survival. We determined that L. delicatula eggs were chill susceptible and the supercooling points of individual eggs ranged from -17.4 °C to -27.7 °C. We observed successful hatch after short- and long-term exposure to temperatures below -20 °C, well below previously published thermal limits for the species. Hatch rates were lower at or below -20 °C in the short exposures, or -15 °C in our long exposures experiments then hatch rate in egg masses not exposed to any treatment. Because L. delicatula eggs survived temperatures near their supercooling points, -27.7 °C could be used as a conservative estimate of the lower lethal temperature for this life stage. Our findings suggest that L. delicatulawill be able to survive in colder climates than initially thought. Of the locations where L. delicatula has been observed in Canada, Winnipeg is the only location where prolonged extreme cold is likely to affect survival. Other regions, such as the Maritimes, southern Ontario, and southern Quebec, do not experience frequent or intense cold spells sufficient to prevent its establishment. Thus, low winter temperatures may not limit L. delicatulaoverwinter survival and establishment in many regions of Canada or other parts of the world that experience similar winter conditions.