Behavioral and biological parameters of six populations of Triatoma pallidipennis (Heteroptera: Reduviidae) from areas with high and low prevalence rates of Trypanosoma cruzi human infection.

In Mexico, more than 30 species of triatomines, vectors of Trypanosoma cruzi, the etiological agent of Chagas disease, have been collected. Among them, Triatoma pallidipennis stands out for its wide geographical distribution, high infection rates and domiciliation. Local populations of triatomines have shown notable biological and behavioral differences, influencing their vectorial capacity. Six behaviors of epidemiological importance, namely, egg-to-adult development time, median number of blood meals to molt to the next instar, instar mortality rates, aggressiveness (delay in initiating a meal), feeding time and defecation delay, were evaluated in this study for six populations of T. pallidipennis. Those populations from central, western and southern Mexico were arranged by pairs with a combination of high (HP) and medium (MP) of Trypanosoma cruzi human infection and most (MFC) and low (CLF) collection frequencies: HP/MFC, HP/CLF, and MP/MFC. The development time was longer in HP/CLF populations (> 220 days). The median number of blood meals to molt was similar (7-9) among five of the six populations. Mortality rates were greater (> 40 %) in HP/CLF and one MP/MFC populations. All studied populations were aggressive but exhibited slight differences among them. The feeding times were similar (≥ 10 min) for all studied populations within instars, increasing as instars progressed. An irregular pattern was observed in defecation behaviors, with marked differences even between the two populations from the same pair. High percentages of young (57.3-87.9 %), and old (62.4-89.8 %) nymphs, of female (61.1-97.3 %) and male (65.7-93.1 %) of all the studied populations defecated quickly (while eating, immediately after finishing feeding or < 1 min postfeeding). Our results indicate that the HP/MFC populations are potentially highly effective vectors for transmitting T. cruzi infections, while HP/CLF populations are potentially less effective vectors T. cruzi infections.

Life history data of a Triatoma protracta nahuatlae, T. sinaloensis, and their laboratory hybrids (Hemiptera: Reduviidae).

Chagas disease is one of the most significant vector-borne diseases in Mexico. The presence of "sylvatic" triatomine vectors of Trypanosoma cruzi (Chagas) inside human dwellings necessitates estimating their vectorial capacity. To estimate this capacity in Triatoma protracta nahuatlae (Ryckman), Triatoma sinaloensis (Ryckman), and their laboratory hybrids, 6 biological parameters were examined. Triatoma sinaloensis exhibited the shortest development time (155 days), with a median of 12 blood meals. Mortality rates varied from 35% to 45% in the 3 studied cohorts. All 3 cohorts were aggressive, initiating feeding within 0.5-1 min, and had similar feeding periods ranging from 10 to 18 min. A majority (75.3-97.9%) of the hybrids defecated when feeding, immediately after feeding, or in less than 1 min post-feeding. In contrast, only 7-42% of nymphs of T. sinaloensis defecated during the same period. Our results regarding the 6 parameters studied confirm the potential role of T. p. nahuatlae as an efficient vector of T. cruzi. Triatoma sinaloensis, on the other hand, exhibited limited vectorial capacity primarily due to its poor defecation behavior. Continued surveillance of these "sylvatic" triatomine populations is necessary to prevent an epidemiological problem.

Vital statistics of the introduced species Triatoma infestans (Klug, 1834) (Hemiptera: Reduviidae) in western Mexico under laboratory conditions.

Triatoma infestans, one of the most important vectors of Trypanosoma cruzi to humans, has recently been discovered introduced in Mexico. Some of the most important biological parameters to estimate the vectorial capacity of a triatomine, such as the hatching of eggs, life cycle, feeding and defecation behaviors for each instar of a population of T. infestans introduced into Mexico are reported. The egg-to-adult development times of the three studied cohorts had a mean of 215.7 days. The mean total number of blood meals required to molt from first-instar nymphs to adults was 11.7. The cumulative mortality was 30.8%. The highest mortality rate was recorded for third-instar nymphs (10.3%), whereas the lowest rate (0.8%) was recorded for first-instar nymphs. All studied specimens began feeding as soon as a blood meal source was offered, showing "aggressive" behavior. Feeding times were ˃ 10 min for all instars, increasing according to instar, in a similar pattern to the development times and the required blood meals before molting. Most (57.7 -82.5%) of the studied specimens of the first- to third-instar nymphs and adults of T. infestans defecated when feeding (WF). The average number of eggs laid per female per day was 0.9, with an eclosion rate of 96.4%. The results of most of the studied parameters confirm the importance of T. infestans wherever it is found because of its potential high capacity for transmitting T. cruzi to hosts. Active entomological surveillance should be carried out in the area of the first discovery of the introduced T. infestans and its surroundings to avoid the dissemination of this effective vector species in Mexico.

Biology of the introduced species Triatoma lecticularia (Hemiptera: Reduviidae) to northwestern Mexico, under laboratory conditions.

The first record of Triatoma lecticularia out of its reported distribution area together with the brief description of the said area is provided in this paper. In addition, some biological parameters related to hatching of eggs, life cycle and feeding and defecation behaviors for each instar of one population of T. lecticularia from its previously reported distribution area (PR) and for each instar of that introduced recently found population (IS) of this species were evaluated and compared. Twenty-eight specimens were collected from IS, mostly (64.29%) from peridomestic areas (mainly chicken coops). No significant (p>0.05) differences were recorded between the two studied cohorts in their average time to hatch, which was close to 19days. The median egg-to-adult development time, the number of blood meals at each nymphal, the instar mortality rates and median time-lapse for beginning of feeding were significantly (p<0.05) shorter for the IS cohort. Median feeding time was higher in PR. Defecation delay was shorter than 10min in both studied cohorts. Given these results, the introduced recently found population of T. lecticularia could be considered an important potential vector of Trypanosoma cruzi to human populations and could replace main triatomine species on its new distribution area.

Biological and genetic aspects of crosses between species of the genus Meccus (Hemiptera: Reduviidae Triatominae).

The degree of reproductive isolation between Meccus phyllosomus and the remaining five species of the genus Meccus, as well as between Meccus bassolsae and Meccus pallidipennis, Meccus longipennis and Meccus picturatus, was examined. Fertility and the segregation of morphological characteristics were examined in two generations of hybrids from crosses between these species. The percentage of couples with offspring (fertile) was high in the vast majority of sets of crosses, with the exception of that between ♀M. phyllosomus and ♂Meccus mazzottii. In sets of crosses involving M. bassolsae specimens, no first-generation (F1) individuals were morphologically similar to M. bassolsae, but instead shared the morphology of the other parental species. A similar phenomenon was observed in most sets of crosses involving M. phyllosomus. These results indicated that different degrees of reproductive isolation exist among the species of Meccus involved in this study. The biological evidence obtained in this study does not support the proposal that M. bassolsae is a full species. It could indicate that, on the contrary, it should be considered a subspecies of a single polytypic species. The biological evidence does support the proposal that M. phyllosomus is a full species.

Biological and genetic aspects of crosses between species of the genus Meccus (Hemiptera: Reduviidae Triatominae)

The degree of reproductive isolation between Meccus phyllosomus and the remaining five species of the genus Meccus, as well as between Meccus bassolsae and Meccus pallidipennis, Meccus longipennis and Meccus picturatus, was examined. Fertility and the segregation of morphological characteristics were examined in two generations of hybrids from crosses between these species. The percentage of couples with offspring (fertile) was high in the vast majority of sets of crosses, with the exception of that between ♀M. phyllosomus and ♂Meccus mazzottii. In sets of crosses involving M. bassolsae specimens, no first-generation (F1) individuals were morphologically similar to M. bassolsae, but instead shared the morphology of the other parental species. A similar phenomenon was observed in most sets of crosses involving M. phyllosomus. These results indicated that different degrees of reproductive isolation exist among the species of Meccus involved in this study. The biological evidence obtained in this study does not support the proposal that M. bassolsae is a full species. It could indicate that, on the contrary, it should be considered a subspecies of a single polytypic species. The biological evidence does support the proposal that M. phyllosomus is a full species.

Influence of the blood meal source on the biology of Meccus longipennis (Hemiptera: Reduviidae) under laboratory conditions.

Influence of the blood meal source on life cycle, mortality, and fecundity of 2 cohorts of recently colonized Mexican Meccus longipennis, fed on hens (H-cohort) or rats (R-cohort) were evaluated in laboratory conditions. One hundred twelve nymphs (56%) (H-cohort) and 102 nymphs (51%) (R-cohort), completed the cycle. The average time from Nymph I to adult was 209+/-41 days (H-cohort) and 239+/-28 days (R-cohort), taking an average of 1.8 (H-cohort) and 1.9 (R-cohort) blood meals per nymphal stage (range 1-6). The average span in days for each stage from the H-cohort was 20.8 for Nymph I, 24.5 for Nymph II, 38.8 for Nymph III, 56.1 for Nymph IV, and 72.5 for Nymph V, and it was 20.2 for Nymph I, 23.1 for Nymph II, 43.2 for Nymph III, 68.8 for Nymph IV, and 75.4 for Nymph V from the R-cohort. The mortality percentage was 44% (H-cohort) and 49% (R-cohort). The average number of eggs laid per female in a 9-month period was 484.1 (range 351.1-847.8) in the H-cohort, whereas the average number of eggs was 442.3 (range 288.5-720.5) in the R-cohort. No significant differences (P > 0.05) were recorded among cohorts fed on the studied blood meal sources, different from most previously studied Triatominae species, perhaps due to a high degree of association of M. longipennis with chickens and hens as much as with mammals under natural conditions on human dwellings.

Feeding, defecation, and development times of Meccus longipennis 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, mortality, and fecundity for each stage of Meccus longipennis life-cycle were evaluated. The bugs were maintained in a dark incubator at 27 ± 1ºC and 80 ± 5 percent rh, were fed weekly and checked daily for ecdysis or death. The hatching rate observed for 300 eggs was 76.7 percent and the average time of hatching was 19.8 days. Mean time-lapse between presentation of the blood meal and the beginning of feeding was under 5 min in nymphal stages and postfeed defecation delay was under 10 min in most stages, except in fourth and fifth stages. Mean feeding time was longer than 10 min in most stages, except in fourth stage. One hundred thirty-one nymphs (N) (65.5 percent) completed the cycle and the average time from NI to adult was 192.6 ± 34.8 days. The average span in days for each stage was 18.1 for NI, 21.4 for NII, 29.5 for NIII, 45.5 for NIV and 55.9 for NV. The number of bloodmeals at each nymphal stage varied from 1 to 5. The mortality rate was 3.29 for NI, 6.8 for NII, 2.92 for NIII 3.76 for NIV, and 10.16 for NV nymphs. The average number of eggs laid per female in a 9-month period was 615.6. Based on our results, we conclude that M. longipennis has some biological and behavioral characteristics which influence its capacity of becoming infected and transmitting Trypanosoma cruzi to human populations in those areas of Mexico where it is currently present.

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.

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 percent (n = 2298) on the group fed on hens and 82.1 percent (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 percent) and 68 fed on rabbits (34 percent), 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

Feeding, defecation, and development times of Meccus longipennis 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, mortality, and fecundity for each stage of Meccus longipennis life-cycle were evaluated. The bugs were maintained in a dark incubator at 27 1 C and 80 5% rh, were fed weekly and checked daily for ecdysis or death. The hatching rate observed for 300 eggs was 76.7% and the average time of hatching was 19.8 days. Mean time-lapse between presentation of the blood meal and the beginning of feeding was under 5 min in nymphal stages and postfeed defecation delay was under 10 min in most stages, except in fourth and fifth stages. Mean feeding time was longer than 10 min in most stages, except in fourth stage. One hundred thirty-one nymphs (N) (65.5%) completed the cycle and the average time from NI to adult was 192.6 34.8 days. The average span in days for each stage was 18.1 for NI, 21.4 for NII, 29.5 for NIII, 45.5 for NIV and 55.9 for NV. The number of bloodmeals at each nymphal stage varied from 1 to 5. The mortality rate was 3.29 for NI, 6.8 for NII, 2.92 for NIII 3.76 for NIV, and 10.16 for NV nymphs. The average number of eggs laid per female in a 9-month period was 615.6. Based on our results, we conclude that M. longipennis has some biological and behavioral characteristics which influence its capacity of becoming infected and transmitting Trypanosoma cruzi to human populations in those areas of Mexico where it is currently present.