Host selection, oviposition behavior and leaf traits of Salix spp. in a specialist willow sawfly

BRACCINI CELINA; ANDREA VEGA; CHLUDIL HUGO DANIEL; FERNANDEZ PATRICIA CARINA

Congreso; 2nd Meeting of the Latin American Association of Chemical Ecology; 2012

Plant genotype often influences plant-herbivore interaction by affecting insect attraction, acceptance and development [1]. Host plant selection by ovipositing females can be crucial for offspring survival [2]. Here, we evaluate the oviposition behavior of the specialist willow sawfly Nematus oligospilus (Hymenoptera: Tenthredinidae) on different genotypes of Salix spp. (Salicaceae) and discuss how it is affected by leaf micromorphology, nutrient levels and secondary metabolites of the host plant. Through choice and no choice bioassays we analyzed host selection according to willow genotype and leaf surface. We also studied larval performance and adult fecundity. For each genotype, leaf micromorphology was described through light and scanning electron microscopy. Total nitrogen and protein contents were quantified, as well as total phenolics, phenolic glycosides and salicin. Results revealed that N. oligospilus clearly prefers to oviposit on S. nigra regardless of leaf side. Even though S. viminalis was the least preferred genotype, it showed better larval performance and higher adult fecundity. Leaf micromorphology analysis showed a tight association between the egg and the leaf, as it is laid inside the epidermis or between the epidermis and the adjacent chlorenchyma. Regarding leaf toughness, S. nigra was lower than S. viminalis and S. babylonica. Quantification of total nitrogen and protein contents revealed higher concentrations on S. viminalis and S. babylonica. Total phenolics and phenolic glycosides were higher and more diverse on S. nigra. Since salicin content levels correlate with oviposition preference, this suggests a role of salicylates as oviposition stimulants. Altogether, results suggest that oviposition preference may be related to lower leaf toughness and ease of injection of female saw-like ovipositor, motivated by the presence of phenolic glycosides. Nitrogen levels may explain better larval performance and adult fecundity in S. viminalis. Thus, a balance among different leaf traits determines the outcomes observed in this study.