BOTH VOLATILES AND EPICUTICULAR PLANT COMPOUNDS DETERMINE OVIPOSITION OF THE WILLOW SAWFLY Nematus oligospilus ON LEAVES OF Salix spp. (SALICACEAE)

CELINA LAURA BRACCINI; VEGA ANDREA SUSANA; COLL ARAOZ MA. VICTORIA; TEAL PETER; JORGE A ZAVALA; FERNANDEZ PATRICIA CARINA

Conferencia; 2015 Conference of the International Society of Chemical Ecology; 2015

Plant volatiles and contact cues play a role in selection and acceptance of host plants by herbivorous insects. Here we studied volatile and contact cues used by the willow sawfly Nematus oligospilus (Hymenoptera: Tenthredinidae) to seek and accept its host plant. First, we recorded behavioral orientation in a Y-tube olfactometer of willow sawfly females to volatiles of the highly preferred genotype Salix nigra and the non-preferred genotype S. viminalis. The volatiles released by undamaged plants were analyzed by coupled gas chromatography-mass spectrometry. Afterwards, we recorded oviposition preference between intact leaves, and leaves in which their cuticular wax layer was removed by means of Arabic gum treatment. Contact cues were evaluated by studying the micromorphology and chemical composition of abaxial and adaxial leaf surfaces. Willow sawfly females oriented preferentially to S. nigra volatiles, which contained significantly higher amounts of (Z) and (E)-β-ocimene, undecane, decanal, and β-caryophyllene. Once on the plant, sawflies laid fewer eggs on S. nigra leaves after Arabic gum treatment, showing the importance of cuticular wax layer. No differences were found among the micromorphology of the leaf surfaces between preferred and non-preferred genotypes. Chemical composition of the cuticular waxes showed higher quantity and diversity of long chain alcohols in the preferred genotype that might be related to oviposition. Our studies suggest that several cues act in concert to provide oviposition cues for N. oligospilus: females are attracted to volatiles from a distance and, once alighting on the plant, they seek specific chemical contact cues in order to lay eggs.