Ammonia attracts the haematophagous bug Triatoma infestans: Behavioural and neurophysiological data on nymphs

1) Nymphs of the haematophagous bug Triatoma infestans (Heteroptera: Reduviidae) are attracted to volatiles from their own faeces on a servosphere. 2) Biological substrates attractive to triatomines release NH3: wetted triatomine faecal papers release NH3 at 256 ppb NH3 from a 60-g source and stale rabbit urine at 394 ppb from 200 ml. Ammonia released from aqueous NH3 also attracts bugs at doses of 3 ppb and 17 ppb on the servosphere. 3) Bugs typically show negative anemotaxis in a stimulus-free air-stream on the servosphere. At onset of stimulation with ammonia from either biological substrates or aqueous NH3 the bugs stop, move their antennae, turn and walk upwind, i.e. odour-mediated anemotaxis. 4) At lower NH3 doses a latency in attraction is recorded, but this latency disappears when the relative humidity of the stimulus delivery air-stream is dropped from 90 to 35%. 5) Electrophysiological recordings from single olfactory sensilla on antennae of Triatoma nymphs reveal two different types of NH3-excited receptors, both within grooved-peg sensilla. The responses of one of these receptor cells to NH3 has been studied in detail and shows that the action potential discharge rate is dose-dependent over the range 2-200 ppb. 6) The amplitudes of electroantennograms recorded from Triatoma nymphs to NH3 are dose dependent over the range 5-550 ppb.