Interazioni piante - insetti: ruolo delle formiche in un sistema multitrofico. Aspetti ecoetologici ed applicativi

This PhD research has analysed some aspects of the relationships that can be established between plants, insect pests, ants and insect predators of pests. In particular we were aimed to understanding, through a series of experiments operated on a multitrophic network, whether the impact of the ant Formica pratensis R. (Hymenoptera: Formicidae) towards the other organisms, could be influenced by the composition of the network in which these species interact and, within these relationships, as was influential the resource represented by aphids on the ants behaviour. Organisms that composed our network were the plant Cucumis sativus L.cv Hoffman’s giganta, infested by the mutualistic aphid Aphis gossypii Glover (Homoptera: Aphididae) or by the non mutualistic aphid Myzus persicae Sulzer (Homoptera: Aphididae), by the chewing feeder Mamestra brassicae L. (Lepidoptera: Noctuidae) and by the aphidophagous predator Aphidoletes aphidimyza R. (Diptera: Cecidomyiidae). Experiments on ants aggressiveness showed that ants have a high predatory potential, completely eradicating the presence of caterpillars on plants. This level of aggressiveness by the way does not grow in the presence of aphids mutualists that should be protected from competitors. The ants also are not able to suppress the predator of aphids that we hypothesize to perform a chemical camouflage, assuming the smells of the aphids in which they feed. We also investigate plant-ant possible interactions. In response to herbivory by insects, several plant species produce volatiles that attract the natural enemies of the herbivores. Although the importance that ants can have in natural and agricultural environment, impacting on the presence of other arthropods subjected to predation or protected because honeydew producers, few works were focused on the importance of the Herbivory Induced Plant Volatiles (HIPVs) as a cue for ants for finding proteins and/or charboidrate sources. Using an open T-olfactometer, we investigated responses of the ant Formica pratensis R. (Hymenoptera: Formicidae) to volatiles emitted by cucumber and potato plants. Cucumis sativus L.cv Hoffman’s giganta was infested by the mutualistic aphid Aphis gossypii Glover (Homoptera: Aphididae) or by the non mutualistic aphid Myzus persicae Sulzer (Homoptera: Aphididae), by the chewing feeder Mamestra brassicae L. (Lepidoptera: Noctuidae) or by the association of A. gossypii and M. brassicae. Solanum tuberosum L. cv Bintje was infested by the same aphids species used for cucumbers, by the chewing feeder Chrysodeixis chalcites Esper (Lepidoptera: Noctuidae) or by the association of A. gossypii and C. chalcites. In dual choice experiments F. pratensis showed interest to volatiles of C. sativus plants infested with chewing caterpillars of M. brassicae alone or in association with A gossypii, over volatiles of undamaged plants or plants damaged by A. gossypii. No statistical relevance had the choice between A. gossypii or M. persicae over undamaged plants. The attraction toward damaged plant volatiles is greater with S. tuberosum plants. In this case ants follow the HIPVs cue of damaged plants either with the chewing feeder C. chalcites, or the sap feeders A. gossypii and M. persicae, over undamaged plants. No choice were shown between potato plants infested with A. gossypii and C. chalcites, over plants infested with A gossypii only. Results shown that ants can react to volatiles emitted by the two plants. The response has different degrees, depending on the plant and insect species. Chewing feeders induce a VOC production that results interesting for ants in both the plant species tested. Aphids induced a VOC emission that only in the case of potato plants induce an interest by the ants.