Effects of w-ACTX-Hv1a/GNA, a novel protein biopesticide targeting voltage-gated calcium ion channels, on target and non-target arthropod species

Abstract

An increasing human population is met with the challenge of feeding over 10 billion people by 2050. Nowadays, over 20% of crop production is lost to insect pests. Chemical control agents, in general, present broad-spectrum activity, killing both pests and beneficial organisms that would contribute to production (i.e. pollinators and natural enemies). Previously, the insecticidal voltage-gated calcium channel blocker peptide ω-ACTX-Hv1a (Hv1a) was linked to the ‘carrier’ molecule snowdrop lectin (GNA). The resulting fusion protein, Hv1a/GNA, is highly toxic towards lepidopteran and coleopteran pests, presenting potential for use as a biopesticide. Here, the fusion protein was shown to also be toxic to the hemipteran pests Sitobion avenae and Myzus persicae, via artificial diet and when expressed in transgenic plants. However, its effects on non-target arthropods have not been previously evaluated. Therefore, toxicity of Hv1a/GNA was tested against two beneficial insects, the parasitoid wasp Eulophus pennicornis via its host, Lacanobia oleracea, and the honeybee Apis mellifera. The fusion protein did not present any significant tri-trophic negative effects on E. pennicornis, even when injected into host larvae. Honeybee survival was slightly affected when fed on high doses of fusion protein representing a ‘worst-case scenario’, but lead to no detectable effects when dosed with field-relevant levels. The fact that bees internalized Hv1a/GNA led to the hypothesis that the haemolymph-feeding parasitic mite Varroa destructor would be affected by the fusion protein. However, mites were able to digest the protein and hence no effects were recorded. Further attempts to target calcium channels in M. persicae and Tribolium castaneum via RNAi were made. Whilst there were no phenotypic effects, gene expression was down-regulated in T. castaneum. This study shows that Hv1a/GNA is a specific biopesticide, posing low risks against beneficial non-target organisms while being toxic to selected insect pests.