José Alejandro Martínez-Ibarra

Role of two Triatoma (Hemiptera: Reduviidae: Triatominae) species in the transmission of Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) to man in the West Coast of Mexico

From August 1997 to August 1998, 334 specimens of Triatoma longipennis and 62 of T. picturata were collected in four groups of localities placed in the zone from Guadalajara, Jalisco to Tepic, Nayarit, in the West Coast of Mexico. Most T. longipennis were collected outdoors (69.2%) while most T. picturata (58.1%) were collected indoors. All collected specimens were examined for Trypanosoma cruzi infection, which was detected on 98 (29.3%) T. longipennis and 17 (27.4%) T. picturata. This study confirms the role of T. longipennis and T. picturata as some of the main T. cruzi vectors to humans in Mexico. Habitation Infestation Rate with T. longipennis was of 0.09 and with T. picturata was of 0.03 and the predominating ecotopes were pile of blocks, chicken coops, pigsties, wall crawls and beds.

Influence of the blood meal source on the biology of Meccus picturatus Usinger 1939 (Hemiptera: Reduviidae: Triatominae) under laboratory conditions

Aspects related to hatching, time-lapse between presenting the blood meal and beginning of feeding, feeding time, postfeed defecation delay,life time, mortality and fecundity for each stage of Meccus picturatus, life-cycle were evaluated and compared in two cohorts of M. picturatus fed on hens or rabbits. The hatching rate observed for each of the two studied groups of eggs was 78.1% (n = 2298) on the group fed on hens and 82.1% (n = 2704) on that fed on rabbits, and the average time of hatching was 20 days. Mean time-lapse for beginning feeding was under 3 min in nymphal stages and postfeed defecation delay was under 10 min in all stages, in both cohorts. Mean feeding time was significantly (P < 0.05) shorter in triatomines fed on hens than on rabbits. A similar number of nymphs of each cohort, 69 fed on hens (34.5%) and 68 fed on rabbits (34%), completed the cycle. No significantly (P > 0.05) differences were recorded among the average times from NI to adult in the cohort fed on hens (196.8 15.8 days) and the average time in the cohort fed on rabbits (189.5 22.9). The average span in days for each stage fed on hens was not significantly different to the average span for each stage fed on rabbits. The number of blood meals at each nymphal stage varied from 1 to 6 in both cohorts. The mortality rates were higher on fifth nymphal stage, in both cohorts. No significant (P > 0.05) differences were recorded on mortality rates on most nymphal stages of both cohorts. The average number of eggs laid per female from the cohort fed on hens in a 9-month period was 791.1, whereas the average number of eggs in the cohort fed on rabbits was 928.3.

Indigenous fish species for the control of Aedes aegypti in water storage tanks in Southern México

Because of inadequate supply of water, inhabitants of five villagesclose to Tapachula, Chiapas, México, store water in cement tanksthat support large populations of Aedes aegypti. Biologicalcontrol using indigenous fish species were studied to control A. aegypti larvae in thosecontainers, since other organisms used as biological control agents areexpensive and unfamiliar to inhabitants of those towns. Other measures(chemical or physical control) are expensive and time consuming. Fiveindigenous fish species, Lepisosteus tropicus (Gill)(Lepisosteiformes: Lepisosteidae), Astyanax fasciatus (Cuvier)(Cypriniformes: Characinidae), Brycon guatemalensis (Regan)(Cypriniformes: Characinidae), Ictalurus meridionalis(Günther) (Cypriniformes: Ictaluridae) and Poecilia sphenopsValenciennes (Cyprinodontiformes: Poeciliidae), currently used asmosquito control agents in the area were tested. Container indexes (ameasure of disease transmission potential) in the tested area werealways zero during the year of the study, independent of towns and fishspecies; this was significantly (P < 0.05) different from containerindexes prior to the test as well as from controls without fish. Nosignificant (P > 0.05) differences were recorded in the efficiency ofthe tested fish species feeding on A. aegypti larvae. Our resultsshow that all tested fish species can be considered as good biologicalagents for controlling A. aegypti larvae in Southern Mexico.

Natural Crossbreeding between Sympatric Species of the Phyllosoma Complex (Insecta: Hemiptera: Reduviidae) Indicate the Existence of Only One Species with Morphologic and Genetic Variations

The nucleotide sequences of the cytochrome B gene and the antennal phenotypes were analyzed for the following triatomine species: Triatoma longipennis, Triatoma pallidipennis, and Triatoma picturata, which belong to the Phyllosoma complex. These species inhabit sympatric areas from Talpa de Allende, Autlan de Navarro, and Teocuitatlan de Corona in Jalisco, Mexico. Molecular marker analysis showed that the sympatric individuals are the natural crossbred descendents of different individuals living in close proximity in these natural areas that resulted in mixed populations. The antennal phenotype results are coincident with these genetic findings, which point to the high similitude between all Phyllosoma complex populations analyzed. These data support the hypothesis that these species are morphotypes with chromatic and genetic varieties, which preserves the possibility of natural breeding with fertile descent. In conclusion, our results strongly support the hypothesis that T. pallidipennis, T. longipennis, and T. picturata are subspecies of the Phyllosoma complex.

Importance of Species of Triatominae (Heteroptera: Reduviidae) in Risk of Transmission of Trypanosoma cruzi in Western Mexico

The epidemiological risk of infection by Trypanosoma cruzi Chagas in human populations of western Mexico is still under study. Although most vectors in this region and their vector capability are already known, new studies estimating the risk and the importance of individual Triatominae species (Hemiptera: Reduviidae) for T. cruzi transmission are necessary. For 1 yr, every month, > 400 human dwellings and their surroundings in eight communities of two western Mexico states were searched for triatomines. More than 1,000 specimens representing four species were collected and checked for T. cruzi infection. Based on the usual entomological indices, only the inhabitants of Gavilán El Progreso-La Villita are at serious risk of vectorial infection by T. cruzi. A population of Meccus longipennis (Usinger) was found living in peridomestic rock pile boundary walls after an insecticide spraying. It was confirmed the major role of peridomestic habitats as shelter areas for triatomines, particularly in rock pile boundary walls and chicken roosts. Triatominae presence also was verified in certain sylvatic habitats, including primarily heaps of stones. The important role of M. longipennis in the potential transmission of T. cruzi in the region and the secondary role of M. picturatus (Usinger) and Triatoma barberi Usinger also were confirmed. Null colonization of houses by T. barberi, which was collected primarily in peridomestic habitats, differs from its common intradomiciliary collection in other studies. Meccus pallidipennis (Stål) most probably does not exist in Nayarit. Meccus mazzottii (Usinger) and Meccus phyllosomus (Burmeister) are no longer found in Nayarit and Jalisco. Additional studies are necessary to determine the current epidemiological situation in other areas of western Mexico.

Biology of Triatoma pallidipennis stal 1945 (Hemiptera: Reduviidae:Triatominae) under laboratory conditions

Aspects related to hatching, life time, mortality, feeding behaviour and fecundity for each stage of Triatoma pallidipennis life-cycle were evaluated. The hatching rate observed for 200 eggs was 60% and the average time of hatching was 18 days. Eighty nymphs (N) (40%) completed the cycle and the average time from NI to adult was 168. 7+/-11.7days. The average span in days for each stage was 18.0 for NI, 18.5 for NII, 30.0 for NIII, 35.7 for NIV and 50.1 for NV. The number of bloodmeals at each nymphal stage varied from 1 to 5. The mortality rate was 9.17 for NI, 5.5 for NII, 6.8 for NIII 4.17 for NIV and 13.04 for NV nymphs. The average number of eggs laid per female in a 9-month period was 498.6. The survival rates of adults were 357+/-217.9 and 262.53+/-167.7 for males and females respectively.

Biology of three species of the Meccus phyllosomus complex (Hemiptera: Reduviidae: Triatominae) fed on blood of hens and rabbits

Aspects related to hatching, life time, number of blood meals to molt, mortality, feeding time and postfeed defecation delay for each instar of Meccus phyllosomus, M. mazzottii, and M. bassolsae, life-cycle were evaluated and compared in two cohorts of each of those three species, fed on hens or rabbits. No significant (p > 0.05) differences were recorded among cohorts fed on hens respect to cohorts fed on rabbits in M. phyllosomus and M. mazzottii and the average time of hatching was 21.5 days for cohorts fed on hens and 22.5 for cohorts fed on rabbits. Average egg-to-adult development times were no significant (p > 0.05) different between both cohorts of M. phyllosomus and M. mazzotti, independent of the blood meal source. The average span in days for each instar fed on hens was not significantly different to the average span for each instar fed on rabbits, when comparisons were made by species. The number of blood meals at each nymphal instar varied from 1 to 6 in both cohorts of each species. The mortality rates were higher on older nymphs, in both cohorts of M. phyllosomus and M. bassolsae, whereas they were higher on first instar nymphs on M. mazzottii. Mean feeding time was no significant (p > 0.05) different in triatomines fed on hens or fed on rabbits, when each species were compared separately. A similar number of nymphs of each cohort, completed the cycle. Defecation delay was no significant (p > 0.05) different when cohorts fed on hens and fed on rabbits were compared by species. Most of the studied parameters showed no significant (p > 0.05) differences among those cohorts fed on hens and for fed on rabbits, which could mean a high degree of association of those species with birds as much as mammals, under wild conditions, increasing their capacity to colonize human dwellings.

Genetic Variation of North American Triatomines (Insecta: Hemiptera: Reduviidae): Initial Divergence between Species and Populations of Chagas Disease Vector

The triatomines vectors of Trypanosoma cruzi are principal factors in acquiring Chagas disease. For this reason, increased knowledge of domestic transmission of T. cruzi and control of its insect vectors is necessary. To contribute to genetic knowledge of North America Triatominae species, we studied genetic variations and conducted phylogenetic analysis of different triatomines species of epidemiologic importance. Our analysis showed high genetic variations between different geographic populations of Triatoma mexicana, Meccus longipennis, M. mazzottii, M. picturatus, and T. dimidiata species, suggested initial divergence, hybridation, or classifications problems. In contrast, T. gerstaeckeri, T. bolivari, and M. pallidipennis populations showed few genetics variations. Analysis using cytochrome B and internal transcribed spacer 2 gene sequences indicated that T. bolivari is closely related to the Rubrofasciata complex and not to T. dimidiata. Triatoma brailovskyi and T. gerstaeckeri showed a close relationship with Dimidiata and Phyllosoma complexes.

Biology of three species of North American Triatominae (Hemiptera: Reduviidae: Triatominae) fed on rabbits

Aspects related to hatching, lifetime, number of blood meals for molting, mortality, feeding time, and postfeeding defecation delay were evaluated and compared in each instar of three North American Triatominae: Triatoma gerstaeckeri, Triatoma lecticularia and Triatoma protracta, all of them fed on rabbits. No significant differences (p > 0.05) were found among the three species regarding mean hatching rate, which was close to 20 days. Egg-to-adult development times were significantly shorter (p < 0.05) for T. lecticularia. Number of blood meals for molting to next instar ranged from one to five for T. protracta, and from one to six for T. gerstaeckeri and T. lecticularia. Mortality rates were higher in younger nymphs of T. lecticularia and T. protracta, while rates in T. gerstaeckeri were higher in fifth-instar nymphs. Mean feeding time was longest in T. gerstaeckeri, followed by T. lecticularia. More than twice the number of T. gerstaeckeri nymphs completed the development process, if compared to the nymphs from the other two species. Defecation delay was less than 10 min for T. lecticularia, T. protracta and the youngest nymphs of T. gerstaeckeri. Results point out that these three species may be important potential vectors of Trypanosoma cruzi for human populations, in areas of Mexico where these species are currently present.

Biological and genetic aspects of experimental hybrids from species of the Phyllosoma complex (Hemiptera: Reduviidae: Triatominae).

The present work is a thorough investigation of the degree of reproductive isolation between Meccus mazzottii and Meccus longipennis, Meccus picturatus, Meccus pallidipennis and Meccus bassolsae, as well as between M. longipennis and M. picturatus. We examined fertility and segregation of morphological characteristics in two generations of hybrids derived from crosses between these species. The percentage of pairs with (fertile) offspring was highest in the set of crosses between M. longipennis and M. picturatus, and lowest between M. mazzottii and M. picturatus. Most first-generation (F1) individuals from crosses involving M. mazzottii were morphologically similar to this species, while only F1 x F1 progeny of parental crosses between M. mazzottii and M. longipennis had offspring second generation that looked like M. mazzottii. The results indicate that different degrees of reproductive isolation apparently exist among the species of the Phyllosoma complex examined in this study. The biological evidence obtained in this study does not support the proposal that M. longipennis and M. picturatus are full species. It could indicate on the contrary, that both could be considered as subspecies of a single polytypic species. On the other hand, biological evidence supports the proposal that M. mazzottii is a full species.