Early herbivory alerts conspecific sawfly females from unsuitable host plants in Salix humboldtiana.

VALLADARES, GABRIELA; COLL ARAOZ MA. VICTORIA; ALDERETE, MARIELA; VERA, M TERESA; FERNANDEZ PATRICIA CARINA

Bariloche

Conferencia; International Conference: Adapting International Conference Adapting Forest Ecosystems and Wood Products to Biotic and Abiotic Stress; 2019

The willow sawfly, Nematus oligospilus (Förster), is a pest in Salix commercial forests and has been reported worldwide. Female host selection is crucial for its offspring as larvae lack the capacity to move to another host. We evaluate the effect of conspecific herbivory on the oviposition choices of sawfly females by providing damaged and undamaged plants of Salix humboldtiana, the only native willow from South America. We estimated the use of olfactory cues by comparing volatile emission of damaged and undamaged plants. We also tested the hypothesis that oviposition site selection maximizes offspring fitness by evaluating neonate hatching, larval performance and survival of larvae that were born and breed on either damaged or undamaged plants.Our results demonstrated that early conspecific herbivory has a dramatic impact in the sawfly N. oligospilus oviposition choices and its offspring performance. The ovipositing female showed a marked preference for laying eggs on undamaged plants of S. humboldtiana and avoided feeding damaged plants in both local and systemic conditions. A quantitative increase of Germacrene D in the profile of damaged plants suggested that it could be related to N. oligospilus avoidance. Furthermore, 48 h of conspecific feeding was sufficient to dramatically impair neonate hatching, as well as larval development and survival, suggesting a rapid and effective reaction of the tree induced resistance mechanisms. These results support the hypothesis that decisions made by colonizing females may result in optimal outcomes for their offspring in a barely study insect model, and also opens the opportunity of studying tree defenses in the unexplored South American willow S. humboldtiana.