Russo, Elia (2023) Bioinsecticides from insect natural antagonists. [Tesi di dottorato]

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Abstract

Ecological and economic sustainability of agricultural production is significantly dependent on the availability of alternative plant protection tools and strategies to replace synthetic pesticides. Bioprotection of crop plants, which includes the use of both biocontrol agents and non-living plant protection tools originated from nature, is the most valid option currently being pursued by the scientific community. Of particular interest is the exploitation of pest suppression mechanisms that insect natural antagonists have evolved, to develop “bio-inspired” pest control measures. This PhD thesis aims to contribute to this research area, by developing new bioinsecticide molecules from virulence factors that natural enemies of pest insects use to subdue their victims. The first part of the thesis focuses on a novel reverse genetic approach in vivo for functional analysis of a venom protein in the aphid parasitoid, Aphidius ervi. RNAi-mediated silencing of the gene encoding the most abundant component of the venom, Ae-γ-glutamyl transpeptidase (Ae-γ-GT), was used to score its impact on parasitized host and parasitoid’s progeny. Our results revealed a new function for this key virulence factor, which plays a crucial role in the fine regulation of the complex interactions between the wasp’s progeny, the host, and its primary bacterial symbiont, Buchnera aphidicola, with important consequences on host nutritional suitability for the developing parasitoid larvae. In the second part, the insecticidal activity of TnBVANK1, a virulence factor belonging to the ANK protein family of the Polydnavirus associated with the parasitoid Toxoneuron nigriceps, was evaluated against aphids, as a basis to develop new pest control strategies for plant sap-sucking insects. This is very much needed, since very few natural molecules are currently available for controlling these pests. The virulence factor considered was orally toxic for the aphid species Acyrthosiphon pisum, exerting a negative impact on the structure and integrity of midgut epithelium. Finally, in the third part, a fusion protein containing a neurotoxic peptide from the venom of a spider and the bovine serum albumin (BSA), as a carrier moiety for mediating transepithelial transport across the midgut barrier, was tested for its oral toxicity against economically important pests in the order Lepidoptera, Hemiptera and Diptera. The obtained results validated the fusion strategy adopted for the delivery of this selective and effective spider toxin. The overall results of this PhD study contribute to the development of new and effective bioprotection tools, providing nice examples on learning from Nature how to control pest insects.

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