Insects mostly use their venom to subdue prey,or for both subduing prey and defense,but some rare species such as larval lepidopterans(caterpillars) use venom solely for deterring predators.Of 133 lepidopteran families, nine can cause serious pathophysiological conditions in humans.Although they present a health hazard,caterpillars are under-represented in venom research and little is known about the structure and function of their toxins.
Limacodidae is a family of more than 1,500 species,over half of which(stinging nettles) have venomous larvae1.Envenomation by limacodids mainly causes pain,itch, and erythema, and occasionally numbness,nausea, and dizziness.Using a combination of imaging technologies,transcriptomics, proteomics and functional assays,we recently provided a holistic portrait of the venom system of one species, Doratifera vulnerans, which produces a complex peptide-rich venom,contrary to the common belief that defensive venoms have simple composition2.Three most abundant families of venom peptides are:(i)disulfide-rich knottins similar to the inhibitor cystine knot (ICK)peptides that dominate spider venoms;(ii) linear,cationic cecropin-like peptides that cause pain in mammals, and also kill bacteria,insects and parasites; and(iii)homologues of adipokinetic hormone/corazonin-related neuropeptide(ACPs)2.
Using proteomics and transcriptomics,I am currently examining the venom of additional limacodid species,including the saddleback caterpillar Acharia stimulea native to eastern North America, and an undescribed species collected in Townsville, Australia. Surprisingly,the North American species venom is very similar to that of the Australian D. vulnerans whereas venom of the undescribed Australian species is radically different,hinting at complex evolution of venom composition within Limacodidae.I am also expanding knowledge of the evolutionary trajectory of individual toxins by synthesising and characterising peptides intermediate in structure between the ancestral cecropin of non-venomous Lepidoptera and D. vulnerans cecropin-like venom toxins.Finally,I am producing a library of limacodid venom peptides using solid-phase peptide synthesis and recombinant expression that I will test on mammalian ion channels including those involved in pain.This research will provide novel insights into multiple aspects of limacodid venoms.