Contact cues determine oviposition of the specialist willow sawfly Nematus oligospilus

BRACCINI, CL; ZAVALA, JA; COLL ARAOZ, MV; FERNANDEZ, PC; BARROZO, RB

Foz do Iguazu

Congreso; 32 Annual Meeting of the International Society of Chemical Ecology/ 4th Congress of the Latin American Association of Chemical Ecology; 2016

Nematus oligopilus is a highly specialized sawfly feeding on selected willows (Salixpp). In the southern  hemisphere, femalesare parthenogenetic. Adults donot seek for food,conspecifics or matingpartners. As soonas they hatch, females look for oviposition sites. This specialization for egg laying suggests a sensory system highlytuned for recognition of suitable oviposition sites. Here we studied the oviposition behavior ofN. oligospilus on two willowgenotypes, a preferred (S. nigra) and a non-preferred one (_S viminalis). First, we performedan ethogram duringthe recognition of the leafsurface before oviposition on both S nigra and S viminalisgenotypes. Second, in order toestimate the importance of leaf cuticular waxes for species recognition, we offered willow leaves as oviposition sites with their cuticularwaxes intact or removed by means of gum Arabie treatment. In addition, we analyzed the polar and non-polar components of the cuticular waxes by chromatography following dichloromethane and methanolextractions of the leaves. Finally, we performeda morphological studyby means of SEM of the antenna and ovipositor of sawflies, in order to look for chemosensory structures.Sawflies spent ca. 40% of their time on the leaf surface of the preferredgenotype while antennating, fanning, tapping with the abdomen end or ovipositing. Conversely, sawflies spent only 20% oftheir time on the less preferred S. viminalisleavesbwhere theybremained mainly quiet or antennating. According to chemicalcues, both polar and non­ polar extractsshowed qualitative differencesamong willow genotypes, suggesting that oviposition cues can be polar, non polar or either kind. Putative chemoreceptor sensilla were found in both, the cerci of the ovipositor and the antenna.Our results suggest thepresence of contact cues on the leaf surface of preferredgenotypes, which seem toincrease locomotoractivity and trigger egg layingin sawflies.