Project description:Plants respond to insect infestation with defenses targeting insect eggs on their leaves and the feeding insects. Upon perceiving cues indicating imminent herbivory, such as damage-induced leaf odors emitted by neighboring plants, they are able to prime their defenses against feeding insects. Yet it remains unknown whether plants can amplify their defenses against insect eggs by responding to cues indicating imminent egg deposition. Here, we tested the hypothesis that a plant strengthens its defenses against insect eggs by responding to insect sex pheromones. Our study shows that preexposure of Pinus sylvestris to pine sawfly sex pheromones reduces the survival rate of subsequently laid sawfly eggs. Exposure to pheromones does not significantly affect the pine needle water content, but results in increased needle hydrogen peroxide concentrations and increased expression of defense-related pine genes such as SOD (superoxide dismutase), LOX (lipoxygenase), PAL (phenylalanine ammonia lyase), and PR-1 (pathogenesis related protein 1) after egg deposition. These results support our hypothesis that plant responses to sex pheromones emitted by an herbivorous insect can boost plant defensive responses to insect egg deposition, thus highlighting the ability of a plant to mobilize its defenses very early against an initial phase of insect attack, the egg deposition.
Project description:Sawflies are important pests of various plant species. Diprion pini (L.) and Neodiprion sertifer (Geoffroy) (Hymenoptera: Diprionidae) are two of the most important sawfly pests in Italy, and both species are parasitized by the hymenopteran parasitoid Dahlbominus fuscipennis (Zetterstedt). Bacterial endosymbionts are currently studied for their high potential in strategies of biocontrol in a number of insect species. In this study, we investigated the presence of symbiotic bacteria (Wolbachia and Cardinium) in the three species of hymenoptera mentioned earlier, both in wild and laboratory populations. Although all samples were negative for the presence of Cardinium, 100% prevalence for Wolbachia was detected, as all examined individuals resulted to be PCR positive. Furthermore, 16S rDNA and ftsZ gene sequencing indicated that all individuals from the three hymenopteran species are infected by a single Wolbachia strain. Additionally, we report the presence of gynandromorphic individuals in D. pini, both in wild and laboratory-reared populations. Heat treatments on D. pini colonies removed the Wolbachia symbionts, but they also prevented the development of adults.
