Insecticide activity of a polydnavirus protein

Polydnaviruses (PDVs) are symbiotic viruses of ichneumonid wasps parasitizing lepidopteran larvae, that are co-injected with the egg and venom into the body of the host insect during parasitization. Viral particles infect host’ tissues, without undergoing replication, and express virulence factors such as peptides and proteins that alter host physiology to increase its suitability for the developing parasitoid progeny. We have extensively studied the PDV associated with the parasitoid Toxoneuron nigriceps (Hymenoptera, Braconidae) and discovered that one of its virulence factors (TnBVANK1) is orally toxic to Spodoptera littoralis (Lepidoptera, Noctuidae). Indeed, this viral protein sticks on the surface of the midgut epithelium and interferes with absorption of nutrients. Here we further explore the oral insecticide activity of this protein on a sap feeder, the aphid species Acyrthosiphon pisum (Hemiptera: Aphididae). Recombinant TnBVANK1 was produced in the yeast Pichia pastoris, purified by affinity chromatography, and administered to aphids ad libitum, via a liquid diet offered in parafilm sachets. A significant increase of aphid mortality was observed over time, showing a clear dose-dependent response. The morphological analyses conducted by means of optical and transmission electron microscopy (TEM) showed an extensive alteration of the midgut epithelium, characterized by severe symptoms of cellular disruption. The mechanism of action is currently being explored. These results indicate that TnBVANK1 is a good candidate for the development of new bioinspired technologies for aphid control, which at the present are very limited.