Feasting on the ordinary or starving for the exceptional!

Global warming is disrupting the finely tuned rhythms of nature, disrupting the intricate synchrony between plants and animals that has evolved over millennia. In our study, we investigated the impact of warmer winter temperatures on the timing of budburst in six common European tree species and the hatching of the spongy moth Lymantria dispar, a generalist leaf-feeding insect whose vitality depends on the timing of egg hatch relative to leaf emergence. If the eggs of the moth hatch too early, the caterpillars will starve, whereas if they hatch too late, they will feed on tougher leaves with defensive compounds synthesized by the plant, resulting in higher mortality and lower development. We exposed eggs of the spongy moth and twig cuttings to four temperature treatments, mimicking warmer winters with reduced chilling temperatures necessary for insect diapause and bud dormancy release. We found that budburst success and twig survival were highest at ambient temperature conditions for all tree species but declined under elevated winter temperatures for certain species like lime or maple trees, likely due to insufficient chilling. While the spongy moth egg hatch aligned well with budburst of the different study tree species under ambient conditions, this synchrony decreased under warmer temperatures, particularly with tree species requiring longer duration of chilling to fully break dormancy. However, egg hatching is perfectly synchronized with the emergence of oak and hornbeam leaves, on which the caterpillars frequently feed and cause considerable damage. Surprisingly, we observed that first-instar gypsy moth larvae showed preference and better development when fed with beech leaves, although the emergence of beech leaves is not synchronized with caterpillar hatching when the climate warms up. Our findings indicate that spongy moth outbreaks are likely to persist in oak and hornbeam forests in western and central Europe as global temperatures continue to rise. This study highlights the complex interactions between species and the need for further research to understand and mitigate the impacts of climate change on ecosystems.