Food web interactions in an ecological community model: Tomato plant, Tuta absoluta and its natural enemies

Abstract

The introduction of an invasive pest in a new area often disrupts the ecological stability existing in a consolidated agricultural system. In this case, the knowledge of the mechanisms of interaction occurring among the species characterizing the food web becomes crucial. In my PhD research activity, I investigated the multitrophic interactions occurring in the ecological model of Tomato, Tuta absoluta and its natural enemies, referring particularly to the omnivorus predator Nesidiocoris tenuis. I conducted behavioral observations on potential intraguild interactions occurring between N. tenuis and the two T. absoluta parasitoids Necremnus tutae and Bracon nigricans. Direct behavioral observations on the mirid were carried out under a microscope supplying T. absoluta larvae parasitized by each of the two parasitoids. Another set of trials was conducted in microcosms to assess the effects of the mirid on the development of both parasitoids. Furthermore, to study the indirect plant responses triggered by the feeding behavior of N. tenuis on tomato plant, we assessed the attraction of the whitefly Bemisia tabaci and its parasitoid Encarsia formosa toward punctured plants by different N. tenuis instars.These data, obtained in olfactory studies, were also related to the analysis of the gene expression involved in the codification for the main phytohormones which lead plant defense and to the analysis of the levels of these phytohormones in healthy and punctured tomato plants. Finally, further studies on the plant-insect interactions were conducted comparing the different attraction of N. tenuis for healthy tomato, the potential companion plants Sesamum indicum and Dittrichia viscosa plants as well as tomato plants infested by T. absoluta eggs and larvae. At the same time gas chromatographic analysis was carried out in order to obtain the volatile profile of each plant to be related with the olfactory studies. These three lines of research provided useful data in the understanding and in the management of the complex interactions in the chosen model. The key role played by the plant in directing these interactions and the competitiveness shown by the zoophytophagous mirid N. tenuis were highlighted. Data evidenced that this omnivorous predator showed to be able to compete with the two parasitoids B. nigricans and N. tutae performing intraguild interferences such as Kleptoparasitism and Intraguild Predation on them. All the feeding instars of N. tenuis were able to induce indirect plant defense in tomato through the activation of the Jasmonic acid pathway responsible for E. formosa attraction and the abscissic acid pathway involved in B. tabaci rejection. Finally in our study with alternative plants, the capability of the mirid to exploit plant biodiversity showing a positive orientation behavior toward potential companion plants of tomato such as sesame emerged; furthermore in these studies we identified volatile compounds emitted by plants potentially responsible for this attraction activity.