Oaks are one of the most important and most common deciduous tree species in the forests of Central Europe, accounting for 10% of the total area. However, due to progressive global warming, the oak is increasingly exposed to biotic and abiotic stressors. In addition to drought and heat, thermophilic herbivorous insects are also a challenge for the oaks.

During studies on the green oak leaf roller (Tortrix vidiana L.) in North Rhine-Westphalia (Germany), differences in the infestation intensity of individual oaks by this herbivorous moth were found, which led to a definition of tolerant (T-oaks, little defoliated) and susceptible (S-oaks, heavily defoliated) oaks.

To validate results from conducted biochemical and molecular studies, ethological studies were carried out with the specialist Tortrix viridana (2013) and the generalist Lymantria dispar L. (gypsy moth) (2019). The parameters used to determine the performance of these herbivorous insects on the two different oak genotypes were developmental time, amount of fed leaves, and mortality of larvae and pupae during the juvenile phase.

While the overall developmental time of green oak leaf roller larvae did not show a significant difference on S- and T-oaks, especially the female larvae of Lymantria dispar needed a longer developmental time on T-oaks.

On T-oaks, larvae of Tortrix viridana had to consume significantly more leaf material to achieve approximately the same pupal weight as larvae fed on S-oaks. In contrast, larvae of the gypsy moth tended to ate less T-oak than S-oak leaf material without revealing differences in pupal weights.

For the green oak leaf roller the mortality of pupae from T-oaks was significantly higher than from S-oaks. For Lymantria dispar no significant differences in mortality was observed.

Basically, T-oaks seem to offer a poorer nutritional and developmental basis for both kinds of leaf-eating insects.