Lepidoptera (moths and butterflies) is a hyperdiverse insect order comprising >150,000 species. Their larvae, caterpillars, have evolved diverse defensive adaptations to protect this highly vulnerable life stage. Such defensive adaptations include protective cases, mimicry of snakes, as well as a variety of toxins. While some toxins are sequestered from plants, others are genetically encoded. Defensive toxins have evolved in at least six groups independently. However, little is known about the molecular basis of toxic defenses employed by many caterpillar groups. We have used techniques spanning genomics, transcriptomics, proteomics, imaging, recombinant expression, peptide synthesis, and bioassays, to investigate the basis of some of the most neglected caterpillar groups.
Zygaenoidea is a superfamily containing many caterpillars with liquid venoms that induce strong pain. In the zygaenoid family Limacodidae, (nettle caterpillars), we find peptide-rich venoms including cecropin-derived peptides, neurohormone-like peptides and disulfide-rich knottins. The cecropin-like peptides have been demonstrated to cause pain in vivo and have been adapted to this function after recruitment of an ancestral antimicrobial cecropin into the venom. In contrast, the closely related zygaenoid family Megalopygidae (asp caterpillars) employ pore-forming toxins that are encoded by genes that were anciently transferred from bacteria to Lepidoptera. We are currently working to understand the evolutionary history of venom use in Zygaenoidea as well as the pharmacology of the many new toxins we have discovered in their venoms.
A different kind of toxic defense is found among processionary caterpillars (Notodontidae: Thaumetopoeinae). These social caterpillars produce miniscule urticating hairs containing toxins that are associated with allergic reactions, as well as equine foetal loss syndrome, which represents a hazard to horses and an economic burden in Australia. We have found a different range of peptides and proteins on these setae, which we are currently characterising.