Abstract

Venoms from the fire ants Solenopsis invicta and S. geminata were free of detectable histamine but caused histamine release from rat peritoneal mast cells in vitro. On a per ant basis, venom from S. invicta ( ed 50 = 0·12 venom reservoirs/ml ) was four times as potent as venom from S. geminata ( ed 50 = 0·54 venom reservoirs/ml ). Hexane extracts of venom and a synthetic piperidine were as effective as the venom itself in producing histamine release, indicating that the piperidines in the venom are responsible for most of the activity. Intradermal injection of venom from S. geminata into human subjects produced dose-dependent wheals and subjective responses (itch and/or pain). Ten nanograms of histamine produced effects approximately equivalent to the venom of a single ant and the antihistamine diphenhydramine significantly reduced the wheal and subjective responses to the venom. It was concluded that histamine release plays a major role in the action of fire ant venoms.

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