Range expansion ofLymantria dispar dispar(L.) (Lepidoptera: Erebidae) along its north‐western margin in North America despite low predicted climatic suitability

Abstract

Aim The European gypsy moth, Lymantria dispar dispar (L.), (Lepidoptera: Erebidae) is an invasive defoliator that has been expanding its range in North America following its introduction in 1869. Here, we investigate recent range expansion into a region previously predicted to be climatically unsuitable. We examine whether winter severity is correlated with summer trap captures of male moths at the landscape scale, and quantify overwintering egg survivorship along a northern boundary of the invasion edge. Location Northern Minnesota, USA. Methods Several winter severity metrics were defined using daily temperature data from 17 weather stations across the study area. These metrics were used to explore associations with male gypsy moth monitoring data (2004–2014). Laboratory‐reared egg masses were deployed to field locations each fall for 2 years in a 2 × 2 factorial design (north/south aspect × below/above snow line) to reflect microclimate variation. Rates of successful egg hatch were assessed the following springs. Results Reductions in summer male moth captures are associated with several metrics of winter severity, such as minimum temperatures. Most egg masses suffered >95% mortality each winter. However, hatching success reached up to 80% in egg masses that had overwintered below the snow line (e.g., <30 cm from the ground). Main Conclusions Our findings that cold winter temperatures are associated with reduced summer trap captures of European gypsy moth, likely due to increased overwintering mortality of exposed egg masses, are consistent with previous predictions of thermal range boundaries for this species. However, high survival in egg masses deposited close to the ground are consistent with thermal escape in subnivean environs (i.e., below snow cover), and suggest that further northward range expansion will be likely in areas that receive measurable annual snowfall.

Impacts of a regional multi-year insect defoliation event on seasonal runoff ratios and instantaneous streamflow characteristics

“…The high probability of increased drought frequency in the Northeastern U.S. with climate change (Hayhoe et al, 2007) could increase the likelihood of L. dispar population irruptions and escalate the rate of L. dispar spread to new forests (Davidson et al, 1999;Liebhold et al, 1994). Lymantria dispar is limited in its geographic range by cold winter temperatures, but warming winters could also facilitate the further range expansion to new regions (Streifel et al, 2019). Our findings support that L. dispar irruptions could have regional implications for hydrological flows at the ecosystem scale, possibly impacting long-term forest function.…”

Climate‐related geographical variation in performance traits across the invasion front of a widespread non‐native insect

“…Much of the foundational work on L. d. dispar thermal biology utilized data derived from a single population to determine how temperature can predict developmental phenology to implement effective management interventions that target specific life stages (e.g., Gray, 2004). Many of these studies focused on the effects of cold temperatures, particularly shortened season lengths in colder climates, the amount of cold necessary for egg hatching and limitations on egg viability constraining northward expansion (Gray et al., 1991; Madrid & Stewart, 1981; Streifel et al., 2019). More recent work has expanded these questions to include warm temperatures (Banahene et al., 2018; Limbu et al., 2017).…”

The Asian gypsy moth (Lymantria disparL.) populations: resistance of eggs to extreme winter temperatures

“…Forecasts of GM range changes should take into account not only the winter temperature, but also dates of formation, stability and depth of snow cover (Sullivan and Wallace, 1972;Smitley et al, 1998;Streifel et al, 2019).…”

“…GM overwinter as eggs deposited in a variety of locations, so it is particularly interesting to study the cold hardiness of the eggs. There is a significant body of research on egg wintering conditions of European and North American populations of L. dispar dispar (Pogue and Schaefer, 2007;Sullivan and Wallace, 1972;Leonard, 1974;Madrid and Stewart, 1981), and new studies appear periodically (Streifel et al, 2019;Fält-Nardmann et al, 2018). According to different sources, the supercooling point of L. dispar dispar eggs varies in the range from -23.6 °C to -30.3 °C.…”