Abstract
The biological control of insect pests is based on the use of natural enemies. However, the growing information on the molecular mechanisms underpinning the interactions between insects and their natural antagonists can be exploited to develop “bio-inspired” pest control strategies, mimicking suppression mechanisms shaped by long co-evolutionary processes. Here we focus on a virulence factor encoded by the polydnavirus associated with the braconid wasp Toxoneuron nigriceps (TnBV), an endophagous parasitoid of noctuid moth larvae. This virulence factor (TnBVANK1) is a member of the viral ankyrin (ANK) protein family, and appears to be involved both in immunosuppression and endocrine alterations of the host. Transgenic tobacco plants expressing TnBVANK1 showed insecticide activity and caused developmental delay in Spodoptera littoralis larvae feeding on them. This effect was more evident in a transgenic line showing a higher number of transcripts of the viral gene. However, this effect was not associated with evidence of translocation into the haemocoel of the entire protein, where the receptors of TnBVANK1 are putatively located. Indeed, immunolocalization experiments evidenced the accumulation of this viral protein in the midgut, where it formed a thick layer coating the brush border of epithelial cells. In vitro transport experiments demonstrated that the presence of recombinant TnBVANK1 exerted a dose-dependent negative impact on amino acid transport. These results open new perspectives for insect control and stimulate additional research efforts to pursue the development of novel bioinsecticides, encoded by parasitoid-derived genes. However, future work will have to carefully evaluate any effect that these molecules may have on beneficial insects and on non-target organisms.
Highlights
The protection of crop plants and of their products against insects has old roots, dating back to the origin of agriculture
In order to localize the transgenic product in the endoplasmic reticulum, the 59 end of the chimeric sequence was fused to the Signal Peptide (SP) of the tobacco PR1a gene, and the 39end to the KDEL sequence [36]
These virulence factors originate from an intense co-evolutionary process among an astonishing number of interacting species [14], which has produced one of the largest reservoirs of natural compounds with potential bioinsecticide activity
Summary
The protection of crop plants and of their products against insects has old roots, dating back to the origin of agriculture. The insecticides have been, and still are, an important tool in intensive agriculture [2, 3], but the unfortunate misuse of these substances has evidenced, over the years, the limits and the poor sustainability of this simplistic approach This has promoted research efforts toward the development of more benign insecticide molecules of natural origin [4] and of integrated pest management (IPM) strategies, more sustainable both from an ecological/toxicological and economic point of view [5, 6], from field level to a broader spatial scale [7]. Molecules like spinosyns [10, 11] are obvious examples of natural insecticides of wide use in IPM, while a number of natural compounds, of plant origin [12] or produced by predatory arthropods [13], are increasingly used or look promising for future developments
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