The venom of a tarantula spider contains a novel protein that is a potent oral insecticide when eaten by the cotton bollworm, an important agricultural pest, Australian scientists report (PLoS ONE doi:10.1371/journal.pone.0073136).
In the wild, the large Australian tarantula, Selenotypus plumipes, inhabits arid grasslands and uses large fangs to inject its prey with venom. The researchers identified a small protein, named orally active insecticidal peptide-1, which they claim is as potent as the synthetic insecticide imidacloprid when consumed by insects. The oral LD50 or lethal dose of this 34-residue peptide required to kill 50% of the targeted bollworm pests was found to be 104.2 pmog/g – the highest activity ever reported for an insecticidal venom peptide given orally. It also acts synergistically with neonicotinoid insecticides.
Cotton bollworm was found to be more sensitive to spider peptide than termites and mealworms, though more tests need to be carried out to see what insects are susceptible. The researchers believe the peptide could be either sprayed or incorporated into transgenic plants.
‘Most of the work on venom-derived bioinsecticides has focused on scorpions,’ notes lead author Glenn King at the University of Queensland, Australia. ‘This does not make a lot of sense as spiders are the most successful insect predators on the planet, with more than 100,000 species.’
His unpublished work suggests all spider venom peptides have some level of oral activity because they have a special structural motif – an inhibitor cysteine – that makes them highly stable. ‘Thus, they hang around long enough in the insect gut that even small rates of uptake across the gut epithelium will still deliver fatal amounts of toxin into the insect hemolymph [bloodstream]. The peptide we discovered is unusual in that its intrinsic level of oral activity is higher than we would have expected.’
‘Chemical pesticides have to be replaced and I think bioinsecticides are the way forward,’ says Natalie Ferry, agricultural biotechnologist, University of Salford, UK. ‘It would be better if we had something more targeted and take out only what we want.’ She says spider venom should be novel as oral insecticides to insects and therefore more effective.
Insect pests reduce work crop yields by 10 to 14%/year. King says this new insecticide may offer distinct advantages: ‘This is an orally active peptide with no contact activity, whereas virtually all chemical insecticides are contact active. This significantly reduces the likelihood of inadvertent effects on beneficial insect predators and pollinators.’
‘Spiders have evolved their venoms over about 300m years to primarily target the insect nervous system. Human chemists have been working on this problem for less than a century,’ he adds. ‘Thus the peptides from spider venom target a wider variety of channels/receptors, they are more selective, and they are not environmentally toxic as they degrade to harmless amino acids.’
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