A comparison of volatiles emitted by adults of three triatomine species

Adult triatomine bugs (Hemiptera: Reduviidae: Triatominae), blood-sucking insect vectors of Chagas’ disease, possess three types of exocrine glands that are absent in nymphs. The paired metasternal glands are located on the ventral metathorax, while the paired Brindley’s glands are situated on the dorsolateral metathorax. In addition, glandular areas associated with the male genitalia were recently described (Weirauch, 2003). Nothing is known about the stimulus for metasternal or genitalia-associated gland secretion in triatomines, but disturbance of adult bugs induces the release of an odour, probably from Brindley’s glands, that is repugnant to the human nose (Kälin & Barrett, 1975; Schofield, 1975). It was reported that Brindley’s gland secretion and the headspace over disturbed adult Triatoma infestans (Klug) consisted of a mixture of carboxylic acids that included isobutyric acid (Hack et al., 1980; Juárez & Brenner, 1981). More recently, Cruz López et al. (1995) analysed Brindley’s gland secretion, and the headspace of disturbed adult T. infestans and found isobutyric acid, together with a mixture of aliphatic alcohols and esters, and aromatic compounds. No carboxylic acid other than isobutyric acid was detected by them, thus contradicting the findings of Hack et al. (1980) and Juárez & Brenner (1981). Analysis of Brindley’s gland secretion of the triatomine Rhodnius prolixus (Stål) suggested the presence of isobutyric acid, other carboxylic acids, and three unidentified esters (Rojas et al., 2002). While the secretion from Brindley’s gland was suggested to represent an alarm signal (Kälin & Barrett, 1975; Schofield, 1975; Barrett, 1976; Ward, 1981), the existence of a sex/ aggregation signal produced by adult triatomines during copulation has also been reported by different authors (Baldwin et al., 1971 for R. prolixus ; Manrique & Lazzari, 1996 and Fontan et al., 2002 for T. infestans ; for a review see Cruz López et al., 2001). Given the variability of the results obtained for T. infestans by previous authors we asked if the blend of odours released by disturbed adult triatomines, supposedly originating in the Brindley’s gland secretion, is characteristic of each species. The headspace vapour over disturbed adults of different triatomine species [ R. prolixus , T. infestans, and Dipetalogaster maxima (Uhler)] that were reared and tested under similar conditions was analysed here. These tests were aided by the use of solid phase micro-extraction (SPME), a technique that does not require the use of solvents for the analysis of volatiles. In addition, efforts were made to identify any mating-associated odour for R. prolixus .