The use of leaf surface contact cues during oviposition explains field preferences in the willow sawfly Nematus oligospilus

BRACCINI, CELINA L.; GERSHENZON, JONATHAN; FERNANDEZ PATRICIA CARINA; BARROZO, ROMINA B.; REICHELT, MICHAEL; DAVILA CAMILA; CERRILLO TERESA; ZAVALA, JORGE A.

Bariloche

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

Once an insect has located and reached a plant, contact cues from the leaf surface determine the final host acceptance. Here we studied the use of Phenolic glycosides (PGs), the main secondary metabolites present in Salicaceae, as contact cues during host location behavior of the willow sawfly Nematus oligospilus (Hymenoptera: Tenthredinidae). First, we described the sequence of behaviors that lead to egg laying on preferred species Salix nigra and non-preferred S. viminalis. Then, we quantified PGs in several commercial willow trees and correlated their presence with oviposition preference of the sawfly in laboratory and natural field conditions. We demonstrated a main role of contact cues in triggering egg laying on the leaf surface of S nigra. In a first step, these cues can be sensed by antennae. A further sensing can be performed by abdominal cerci, which in turn triggers egg laying in sawflies. Our results also suggest that PGs are important cues on the leaf surface for female oviposition. Moreover, we determined that commercial willow hybrids lacking PGs are not preferred for oviposition. Identifying host plant resistance requires recognizing susceptibility factors that favor host finding by pests. Phenolic glycosides normally acting as defenses, can act as a susceptibility factor by triggering oviposition in this willow sawfly. These defensive compounds could be selected against to increase resistance in willows to evade such a specialist pest. This can be also applied by development of screening methods for early detection of susceptibility to this sawfly during the selection of new varieties in willow breeding programs.