Isolation of an orally active insecticidal toxin from the venom of an Australian tarantula

Many insect pests have developed resistance to existing chemical insecticides and consequently there is much interest in the development of new insecticidal compounds with novel modes of action. Although spiders have deployed insecticidal toxins in their venoms for over 250 million years, there is no evolutionary selection pressure on these toxins to possess oral activity since they are injected into prey and predators via a hypodermic needle-like fang. Thus, it has been assumed that spider-venom peptides are not orally active and are therefore unlikely to be useful insecticides. Contrary to this dogma, we show that it is possible to isolate spider-venom peptides with high levels of oral insecticidal activity by directly screening for per os toxicity. Using this approach, we isolated a 34-residue orally active insecticidal peptide (OAIP-1) from venom of the Australian tarantula Selenotypus plumipes. The oral LD50 for OAIP-1 in the agronomically important cotton bollworm Helicoverpa armigera was 104.2 +/- 0.6 pmol/g, which is the highest per os activity reported to date for an insecticidal venom peptide. OAIP-1 is equipotent with synthetic pyrethroids and it acts synergistically with neonicotinoid insecticides. The three-dimensional structure of OAIP-1 determined using NMR spectroscopy revealed that the three disulfide bonds form an inhibitor cystine knot motif; this structural motif provides the peptide with a high level of biological stability that probably contributes to its oral activity. OAIP-1 is likely to be synergized by the gut-lytic activity of the Bacillus thuringiensis Cry toxin (Bt) expressed in insect-resistant transgenic crops, and consequently it might be a good candidate for trait stacking with Bt

The venom of Australian spiders

Australia is home to an estimated 10,000 species of spider, including species from the Latrodectus genera and Atracinae family, two of the four widely recognized medically significant spider groups. It is predicted in excess of 5,000 spider bite cases occurring annually in Australia, predominantly by spiders that have not shown any medical relevance. Bites by medically relevant spiders are rare, and of those treatment with antivenom is rarer. Despite extensive publicity and rumor, there is no conclusive evidence that the venom of any Australian spiders is responsible for necrotic arachnidism. The complexity and diversity of spider venoms, combined with potent activity on a range of targets in mammalian and insect systems, have attracted interest in the potential of spider venoms as a source of insecticidal and therapeutic leads. The venom of species of Australian funnel-web spider has received the most attention for study, with more than 75 venom peptides identified from nine toxin families. Recent work has identified venom peptides from the venom of Australian tarantulas with potential as insecticidal and therapeutic leads. This chapter provides an overview of spiders in Australia and their medical and clinical importance and provides a current comprehensive review of the published toxins from Australian spider venoms