Temporal dynamics of flight muscle development in Triatoma infestans (Hemiptera: Reduviidae)

Triatoma infestans Klug is dimorphic for flight muscles. This dimorphism may affect flight dispersal, reinfestation patterns, and transmission risk. To understand the contributions of genes and environment to morph determination, it is first necessary to characterize the temporal dynamics of flight muscle development. Field-collected T. infestans adults were dissected 20 or 100 d after collection, and those collected as nymphs were dissected at approximately 4, 15, or 44 d after the imaginal molt. The occurrence of flight muscles was additionally assessed by minimally invasive, repeated observations through the scutum of live bugs. Overall, 33.5% of 179 males and 7.8% of 179 females had no flight muscles. Neither dissections nor repeated observations evidenced changes in morph type during adult life, suggesting that the occurrence of flight muscles is mostly irreversible within the time span of observations and is determined before or during final ecdysis. Flight muscles were detectable at 4 d after emergence and achieved complete development within 4-15 d after emergence. The repeated observation of thoracic contents through the scutum showed very high sensitivity and specificity and apparently had minor effects on mortality. In another bug population located 360 km away, 16.4% of 177 males and 6.7% of 149 females had no flight muscles. Current results show that the sex-biased flight muscle dimorphism is a regionally widespread character in T. infestans. This character should be considered in field population studies that seek to measure reinfestation risk and dispersal in T. infestans and other Triatominae.

Spatiotemporal patterns of reinfestation by Triatoma guasayana (Hemiptera: Reduviidae) in a rural community of northwestern Argentina

Triatoma guasayana (Wygodzinsky & Abalos) is a secondary vector of Trypanosoma cruzi (Chagas), the etiologic agent of Chagas disease, in the Chaco region of Argentina, Bolivia, and Paraguay. The spatial distribution of T. guasayana in a rural community in northwestern Argentina is described and analyzed using very high spatial resolution satellite imagery, geographic information systems, and spatial statistics. Since a 1992 residual spraying with insecticides of all houses, site-specific domestic and peridomestic reinfestations by triatomine bugs were monitored using various methods semiannually from 1993 to 2002. The reinfestation by T. guasayana started with finding of only adult bugs in a few sites. Bug abundance was significantly clustered and predominantly peridomestic in the southern and northern extremes of the community. The identified source of reinfestation in the northern cluster was a colonized wood pile, whereas no potential peridomestic source was found for the southern cluster. The spatial distribution of T. guasayana was positively associated with the abundance and spatial distribution of goats. Active dispersal from the hypothesized source and the surrounding sylvatic environment, and passive transport of bugs in wood piles seems to be the most likely mechanisms underlying the observed spatial pattern of T. guasayana. The absence of domestic colonization indicates that, to date, there is no trend toward increased local domiciliation of T. guasayana. The clustering zones can be considered "hot spots" where bug invasion from other sources is expected to be higher and where eventually, introduction of sylvatic T. cruzi to suitable hosts may occur.

Spatial structuring of Triatoma infestans (Hemiptera, Reduviidae) populations from northwestern Argentina using wing geometric morphometry

Wing geometric morphometry was used to study the spatial structuring of populations of Triatoma infestans from different villages, ecotopes, and sites within a village in northwestern Argentina. A total of 308 male and 197 female wings of T. infestans collected from peridomestic and domestic ecotopes in March 2000 was analyzed. On average, female bugs had a significantly larger wing size than males. Triatomines collected from domiciles or structures associated with chickens had larger wings than bugs collected from goat or pig corrals. The wing size of bugs did not differ significantly between villages. Discriminant analyses of wing shape showed significant divergence between villages, ecotopes, and individual collection sites. The study of metric variation of males between sites belonging to the same ecotope also revealed significant heterogeneity. Indeed, within the same section of the village the difference between two goat corrals was sometimes greater than that between neighboring goat and pig corrals. Thus, morphometric heterogeneity within villages may be the result not only of ecotope and host associations, but also of physical isolation between subunits. The strong structuring of T. infestans populations in the study area indicates that recolonization could be traced back to a small geographic source.

Active dispersal of natural populations of Triatoma infestans (Hemiptera: Reduviidae) in rural northwestern Argentina

An empirical model of flight initiation coupled with data from a longitudinal study predicted that the flight dispersal of Triatoma infestans from peridomestic sites was more likely to occur in late summer. To partially test this prediction, we operated 11-12 black light traps from 1945 to 2200 hours in March 2003 in two villages in northern Argentina. All peridomestic sites around the light traps were later inspected to assess the relative abundance and nutritional status of T. infestans at each site. Traps were located 19-94 m from the nearest infested site. A total of 2 female, 10 male, and 3 fifth-instar nymphs of T. infestans; 4 adult Triatoma garciabesi; and 1 Triatoma guasayana fifth-instar nymph were collected in 64 trap nights. Nearly two-thirds of the bugs arrived to the traps during the first hour after sunset, when ambient temperatures were 22-28 degrees C; 80% of adults were unfed. The number of T. infestans that flew to the traps was significantly and negatively associated with wind speed, and the number of males positively associated with the abundance of adult T. infestans in peridomestic sites within 200 m around each light trap. This is the first successful application of light traps for collecting dispersing nymphal and adult T. infestans on a village-wide scale. We attribute this success to the placement of traps with consideration to spatial infestation patterns and seasonal variation in nutritional status of peridomestic triatomine populations.