Acta Tropica 77 (2000) 271 – 278 Two different vibratory signals in Rhodnius prolixus (Hemiptera: Reduviidae) G. Manrique *,P.E. Schilman 1 Departamento de Cs. Biolo´ gicas, Facultad de Ciencias Exactas y Naturales, Uni6ersidad de Buenos Aires, Ciudad Uni6ersitaria, 1428 Buenos Aires, Argentina Received 16 July 2000; received in revised form 27 July 2000; accepted 14 August 2000 Abstract In this study the substrate-borne stridulatory vibrations produced by Rhodnius prolixus females were recorded and analysed in two different behavioural contexts.In the contextof sexualcommunication females spontaneously stridulated to reject copulatory attempts performed by males. These male-deterring stridulations were fully effective: out of 61 attempts, no copulation occurred. These stridulations consisted of short series of repetitive syllables, each one composed by a single chirp. In the contextof defensive behaviour, bugs stridulated if they were clasped or restrained. These disturbance stridulations consisted of long series of repetitive syllables, each one composed by a series of short chirps and a long one. Male-deterring and disturbance stridulations differed in their temporal pattern and frequency spectra, having a main carrier frequency of about 1500 and 2200 Hz, respectively. As no differences in the inter-ridge distances along the whole stridulatory organ were found, the differences in the frequency between both signals could be explained on the basis of a different velocity of rubbing of the proboscis against the prosternal stridulatory organ. It was found that R. prolixus and the related species Triatoma infestans rubbed only the central region of the stridulatory groove (around 1/3 of the total length) to produce disturbance stridulations. The results are discussed in relation to previous work on vibrational sensitivity in R. prolixus and are also compared with results reported for T. infestans. © 2000 Elsevier Science B.V. All rights reserved. Keywords : Rhodnius prolixus; Stridulation;Sexualbehavior;Vibratory communication; Defensive behavior; Mechanoreception www.elsevier.com/locate/actatropica 1.Introduction Rhodnius prolixus and Triatoma infestans (Hemiptera, Reduviidae, Triatominae) are haema- tophagous bugs of medical importance as vectors of the flagellate Trypanosoma cruzi responsible for Chagas Disease in South America (Zeledo´ n and Rabinovich, 1981).Vibrational communication has been observed in manyarthropod species (Markl, 1983). Triatomine bugs are not an excep- tion: they stridulateby rubbing thetip of the proboscis against the striated cuticular prosternal groove (Schofield, 1977;DiLuciano,1981).Such * Corresponding author. Fax: + 54-11-45763384. E-mail address : gabo@bg.fcen.uba.ar (G. Manrique). 1 Presentaddress:Theodor-Boveri-Institut, Lehrstuhl fu¨ r Verthaltensphysiologie und Soziobiologie der Universita¨t, Am Hubland,D 97074 Wu¨ rzburg, Germany. 0001-706X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 1 - 7 0 6 X ( 0 0 ) 0 0 1 4 6 - 7