Conspecific insect herbivores co-occurring on the same host plant interact both directly through interference competition and indirectly through exploitative competition, plant-mediated and enemy-mediated interactions. The situation is however less clear when interactions among conspecific insect herbivores are separated in time over the course of the same growing season such as in multivoltine herbivore species. We hypothesized that early season herbivory would result in reduced egg deposition and lower next generation herbivore performance on previously attacked plants. We experimentally tested this hypothesis in a choice experiment with box tree moth females, Cydalima perspectalis Walker (Lepidoptera: Crambidae), offered box trees, Buxus sempervirens L. (Buxaceae), that had been, or not, previously defoliated by BTM larvae earlier in the season. We further compared the performance of next generation larvae on previously damaged vs undamaged plants. Prior herbivory had no effect on egg laying behaviour, but next generation larval weight was significantly lower in previously damaged plants. There was a negative correlation between the number of egg clutches per plant and larval performance. Altogether, our findings reveal that early season herbivory reduces the performance of conspecific individuals on the same host plant later in the plant growing season, and that this time-lagged intraspecific competition results from a mismatch between female oviposition preference and the performance of its offspring.

Conspecific insect herbivores co-occurring on the same host plant interact both directly through interference competition and indirectly through exploitative competition, plantmediated interactions and enemy-mediated interactions. However, the situation is less clear when the interactions between conspecific insect herbivores are separated in time within the same growing season, as it is the case for multivoltine species. We hypothesized that early season herbivory would result in reduced egg laying and reduced performance of the next generation of herbivores on previously attacked plants. We tested this hypothesis in a choice experiment with box tree moth females (Cydalima perspectalis Walker, Lepidoptera: Crambidae). These females were exposed to box trees (Buxus sempervirens L., Buxaceae) that were either undamaged or attacked by conspecific larvae earlier in the season. We then compared the performance of the next generation larvae on previously damaged vs undamaged plants. Previous herbivory had no effect on oviposition behaviour, but the weight of next generation larvae was significantly lower in previously damaged plants. There was a negative correlation between the number of egg clutches laid on plants by the first generation and the performance of the next generation larvae. Overall, our findings reveal that early season herbivory reduces the performance of conspecific individuals on the same host plant later in the growing season, and that this time-lagged intraspecific competition results from a mismatch between the oviposition preference of females and the performance of its offspring.

Insect herbivores co-occurring on the same host plant interact in various ways. In particular, early-season insect herbivory triggers a wide range of plant responses that can determine the performance of herbivores colonizing the plant later in the course of the season. But the strength and direction of such effects are debated, and virtually unknown in the case of novel interactions involving exotic insects in their introduction range. We conducted an observational field study in SW France, a region recently invaded by the Oak Lace Bug (OLB, Corythucha arcuata Say). We measured early chewing damage and subsequent OLB damage in four oak species (Quercus robur, Q. pubescens, Q. cerris and Q. ilex). We set up a complementary non-choice experiment in the laboratory, feeding OLB with leaves with or without prior herbivory. The four oak species differed in their sensitivity to OLB damage, Q. ilex being broadly resistant. Prior herbivory promoted OLB damage in the laboratory experiment, but not in the field. However, prior herbivory did not alter the rank of oak resistance to the OLB. Our results suggest possible synergistic effects between spring defoliators and the OLB. This study brings insight into herbivore-herbivore interactions and their possible implications for forest management.