Winter warming effects on overwinter survival, energy use, and spring emergence of Cerotoma trifurcata (Coleoptera: Chrysomelidae)

Bean leaf beetle Cerotoma trifurcata (Förster) (Coleoptera: Chrysomelidae) is a pest of soybean in the U.S.A. and is becoming a concern in Canada. The projected increase in winter temperatures under climate change could affect overwinter survival, timing of spring emergence and, ultimately, the severity of this pest. We assessed the potential effects of warmer winters in field experiments performed in three consecutive years. Three warming levels were applied: (i) heated approximately 4 °C above ambient; (ii) unheated with snow cover left intact; and (iii) unheated with snow cover removed. Survival and date of emergence were assessed in all years, and beetle lipid content was analyzed in 1 year to determine rates of energy use. Overwinter survival was 6.5–14.5% among years. Winter warming inconsistently affected overwinter survival: increasing survival in one winter, decreasing survival in the warmest winter and having no effect in one winter. Beetles that received supplemental winter warming emerged approximately 2 weeks earlier in spring, and lipid content did not differ among treatment groups. Earlier spring emergence may allow for the production of an additional generation per year of C. trifurcata under future climate change. However, further experiments are required to establish the relationship between overwinter survival and subsequent beetle population growth to determine potential pest status and best management practices under future climate conditions.