THE ROLE OF PHENOLIC GLYCOSIDES DURING HOST LOCATION BEHAVIOR OF THE WILLOW SAWFLY Nematus oligospilus

BRACCINI CELINA; BARROZO ROMINA; DAVILA CAMILA; COLL ARAOZ MA. VICTORIA; GERSHENZON JONATHAN; REICHELT MICHAEL; JORGE A ZAVALA; FERNANDEZ PATRICIA CARINA

Simposio; XV European Symposium of Insect Taste and Olfaction; 2017

Once an insect has located and reached a plant, contact cues from the leaf surface determine final host acceptance. The outermost leaf surface possesses an epicuticular wax layer which consists mostly of very long chain aliphatic wax components. Previous studies show that the epicuticular wax composition of Salix spp. plays a role in the selection of preferred and non-preferred willow genotypes by the willow sawfly Nematus oligospilus (Hymenoptera: Tenthredinidae). However, in several insect species, epicuticular wax compounds act in synergism with secondary metabolites as oviposition stimulants. Phenolic glycosides are the most important secondary metabolites present in Salicaceae. We investigated if these compounds might have a role in host recognition of preferred Salix genotypes by N. oligospilus females. More specifically, we first determined the sequence of behaviors of the ovipositing females after contacting the leaf surface of preferred (S. nigra) and non-preferred (S. viminalis) species. Second, we evaluated differences in the chemistry of phenolic glycosides present on the cuticular surface of preferred and non-preferred willow genotypes. Then we studied the morphology and electrophysiological response of chemosensory structures present on female?s antennae and ovipositor with which females could detect host plant cues. Finally, we performed single sensillum recordings from chemosensory sensilla to phenolic glycosides differentially present in both experimental genotypes. Our results suggest the presence of contact cues on the leaf surface of preferred genotypes, which increase ovipositor probing and trigger egg laying in sawflies. Phenolic glycosides present on the leaf surface seem to be part of a chemical signature that this highly specialized insect seeks on host plants. Chaetic chemosensory sensilla present in antennae and cerci of the ovipositor are sensitive to salicin and may play a role in the detection of phenolic glycosides.