Abstract
Assassin bugs (Reduviidae) produce venoms that are insecticidal, and which induce pain in predators, but the composition and function of their individual venom components is poorly understood. We report findings on the venom system of the red-spotted assassin bug Platymeris rhadamanthus, a large species of African origin that is unique in propelling venom as a projectile weapon when threatened. We performed RNA sequencing experiments on venom glands (separate transcriptomes of the posterior main gland, PMG, and the anterior main gland, AMG), and proteomic experiments on venom that was either defensively propelled or collected from the proboscis in response to electrostimulation. We resolved a venom proteome comprising 166 polypeptides. Both defensively propelled venom and most venom samples collected in response to electrostimulation show a protein profile similar to the predicted secretory products of the PMG, with a smaller contribution from the AMG. Pooled venom samples induce calcium influx via membrane lysis when applied to mammalian neuronal cells, consistent with their ability to cause pain when propelled into the eyes or mucus membranes of potential predators. The same venom induces rapid paralysis and death when injected into fruit flies. These data suggest that the cytolytic, insecticidal venom used by reduviids to capture prey is also a highly effective defensive weapon when propelled at predators.
Highlights
The practice of spraying or propelling venom against potential predators has evolved in diverse animal taxa including snakes, spiders, ants, wasps, and assassin bugs
Since we previously demonstrated that harassment of Pristhesancus plagipennis elicits the secretory products of the anterior main gland (AMG), we hypothesised that venom propelled defensively by Platymeris rhadamanthus might be partly or wholly produced by the AMG
These data support our previous observations that the composition of heteropteran venom is highly conserved through evolutionary time in the absence of trophic transitions [19], a feature that has been noted for some other groups of venomous animal [33]
Summary
The practice of spraying or propelling venom against potential predators has evolved in diverse animal taxa including snakes, spiders, ants, wasps, and assassin bugs. Projectile use of venom has evolved three times, once in genus Hemachatus and twice in genus Naja [1]. Spitting cobras propel venom with high accuracy up to 2 m [2], and the venom can cause permanent blindness if it contacts human eyes [3]. Workers of the social vespid wasp Parachartergus colobopterus [6], formicine ants [7], and the lynx spider Peucetia viridans have been reported to propel venom defensively [8]. Spitting spiders (Scytodes sp.) uniquely propel a sticky material from their venom glands to immobilise prey mechanically, as well as practising more conventional envenomation [9]
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