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Bionomics of populations of Meccus pallidipennis (Stål), 1872 (Hemiptera: Reduviidae) from Mexico

2012; Wiley; Volume: 37; Issue: 2 Linguagem: Inglês

10.1111/j.1948-7134.2012.00255.x

1948-7134

José Alejandro Martínez‐Ibarra, Benjamín Nogueda‐Torres, Gerardo García-Benavídez, Víctor Vargas-Llamas, Rafael Bustos-Saldaña, Oziel Dante Montañez‐Valdez,

Parasitic Diseases Research and Treatment

Together with the six other species of the Phyllosoma complex, Meccus pallidipennis (Stal, 1872) is considered to be responsible for 74% of the vectorial transmission of Trypanosoma cruzi (Chagas, 1909), the causative agent of Chagas disease, to humans in Mexico (Ibarra-Cerdeña et al. 2009). Meccus pallidipennis is distributed in nine states throughout western, central, and southern Mexico where it is considered an important vector of T. cruzi (Salazar-Schettino et al. 2010, Martínez-Ibarra et al. 2011, Benítez-Alva et al. 2012). Significant differences in the number of people infected have been recorded in different states where M. pallidipennis is distributed, which was associated with different degrees of invasion in human dwellings (Ramsey et al. 2003, Martínez-Ibarra et al. 2011). According to Schofield (1985), the biological features and behaviors of triatomines appear to vary with the local conditions. Genetic studies of M. longipennis (a species that is closely related to M. pallidipennis) populations in Mexico using molecular markers detected major differences on a microgeographical scale in domestic and sylvatic environments (Breniere et al. 2012). Different biological traits have been studied on triatomines and some other vector species and it was concluded that they are important criteria for determining the relationships among species or populations within the same species (Carbajal de la Fuente et al. 2010, Grech et al. 2010, Martínez-Ibarra et al. 2012a). A study was conducted using three populations of M. pallidipennis from western, central, and southern Mexico to analyze their feeding behavior and life cycles and evaluate potential effects on the transmission of T. cruzi to human hosts. Three laboratory colonies of M. pallidipennis were established in 2010 using at least 30 specimens collected from localities with different environmental characteristics in three different Mexican states, i.e., Taretan in the state of Michoacán, Amilcingo in the state of Morelos, and Mariscala de Juárez in the state of Oaxaca (Figure 1). Taretan (19°23′ N, 101°57′W) is located 1,130 m above sea level with a temperate climate and it is characterized by the presence of sapodilla (Casimiroa edulis La Llave & Lex.), tepehuaje, (Lysiloma acapulcensis (Kunth) Benth), mango (Mangifera indica L.), pine (Pinus spp. L.), holm oak, and oak forest (Quercus spp. L.). Amilcingo (18°74′ N, 98o76′ W) is located 1,500 m above sea level with a temperate subhumid climate and it is characterized by the presence of jacaranda (Jacaranda spp. Juss), peacock flower (Caesalpinia pulcherrima (L.) Sw), peanut (Arachis hypogaea L.), and bougainvillea (Bougainvillea glabra Choisy). Mariscala de Juárez (17°45′ N, 98°09′ W) is located 1,080 m above sea level with a hot climate and it is characterized by the presence of holm oak and oak forest, guamúchil (Pithecellobium dulce (Roxb) Benth), and wild fig (Ficus glabrata H B K). Locations where the populations were initially collected (circles in inset) from Michoacán, Morelos, and Oaxaca states, Mexico (1: Taretan, 2: Amilcingo, 3: Mariscala de Juárez). The specimens were identified according to the taxonomic key of Lent and Wygodzinsky (1979), taking into account the revalidation of the genus Meccus (Carcavallo et al. 2000). Study colonies were maintained in similar conditions to those used in a previously published study on the biology of M. pallidipennis (Martínez-Ibarra and Novelo-López 2004), i.e., 27 ± 1°C and 75 ± 5% relative humidity (RH). Individuals were fed on immobilized and anesthetized New Zealand rabbits (Oryctolagus cuniculus, L.) on a weekly basis. The rabbits were anesthetized according to the Norma Oficial Mexicana regulations using 0.25 ml/kg of ketamine, which was applied intramuscularly according to established guidelines. Eggs from each colony were grouped based on the date of oviposition to initiate a cohort for each population, each containing 100 eggs. After eclosion, a group of 1st instar nymphs were separated individually from each population into plastic containers (5.5 cm diameter × 10.5 cm height), with a central support of absorbent cardboard. Three days after eclosion, each cohort of nymphs was fed individually on New Zealand rabbits during a 1-h period and subsequent blood meals were provided on a fortnightly basis. Nymphs were observed at the end of feeding to record blood ingestion, in order to know the number of blood meals necessary to molt. Bugs were maintained in an incubator at 27 ± 1° C and 75 ± 5% RH, with a 12/12 h (light/dark) regime, and were checked daily for ecdysis or death. The percentages of females and males in each study cohort were recorded at the end of the cycle. Of the insects that completed their development to the adult instar, ten adult pairs from each cohort were placed into individual containers (5.5 cm diameter × 10.5 cm height) and maintained as previously described to determine their oviposition patterns. Eggs were collected every day for 30 days and placed into individual containers for hatching. A nonparametric Kruskal-Wallis test was used to compare the amount of eggs laid per female, the developmental cycle periods, and the number of blood meals before molt in the three cohorts studied. Bartlett's tests indicated P<0 for all comparisons. Pairwise comparisons were used for intergroup comparisons by Dunn's method. The chi square test was used to compare frequencies. Differences were considered significant when P<0.05. The average 1st instar nymph to adult development time was significantly longer (H=47.58, d.f.=2, P 0.05) differences between the Amilcingo and Mariscala de Juárez cohorts. Nymphal development times increased as a function of the nymphal instar period in the three cohorts studied (Table 1). The average numbers of blood meals between the molt and the next instar in the Amilcingo population was significantly lower (H=41.89, d.f.=2, P 0.05) between the Taretan and Mariscala de Juárez populations. The average number of blood meals increased as a function of the nymphal instar period in the three cohorts studied (Table 1). Mortality rates were slightly higher in the Amilcingo population, although there were no significant differences (χ2=0.89, d.f.=2, P>0.05) among the three populations studied (Table 1). At the end of the cycles, the percentages of females produced were not significantly different (χ2=0.29, d.f.=2, P>0.05) among the three populations (Table 2). The mean number of eggs laid per female per day by the population from Taretan was significantly higher (H=35.22, d.f.=2, P 0.05) among the three cohorts studied (Table 2). There were also no significant differences (H=5.04, d.f.=2, P>0.05) in the average incubation periods of the three cohorts (Table 1). The average egg-to-adult development time in the three study cohorts was short (around five months), which reflects that the laboratory conditions were favorable to the development of M. pallidipennis. That average development time was shorter than the development time of some Mexican-related species such as M. longipennis (Usinger, 1939) and T. recurva (Stål, 1868) (Martínez-Ibarra et al. 2012a,b), considered among the most important vectors of T. cruzi in Mexico (Salazar-Schettino et al. 2010). These results could also suggest that there is a potential risk of an increase in any of those populations in favorable conditions, which might lead to an increased risk of T. cruzi transmission to hosts in their distributions areas. On average, approximately 70–80% of instars in each of the study cohorts from Taretan and Mariscala de Juárez required two or more meals to molt to the next instar, whereas the cohort from Amilcingo required only 1.5 meals to molt. The requirement for more blood meals represents an increased incidence of contact between the vector and host, which could lead to an increased infection rate by T. cruzi in humans, because M. pallidipennis usually defecates soon after feeding (Martínez-Ibarra and Novelo-López 2004). Those differences in the potential number of vector-human contacts might help explain the greater incidence of human serological cases in the states of Michoacán and Oaxaca (>8,000 per year) compared with Morelos (<2,000 per year) (Ramsey et al. 2003). Mortality rates were low and similar to those of some related triatomine species, such as T. maculata, Erichson, 1848, T. dimidiata Latreille, 1811, and M. longipennis (Feliciangeli and Rabinovich 1985, Reyes and Angulo 2009, Martínez-Ibarra et al. 2012a) and to M. pallidipennis in a previous study (Martínez-Ibarra and Novelo-López 2004). Most of these species are considered to be important vectors of Chagas disease in their distribution areas (Salazar-Schettino et al. 2010). Those low mortality rates could mean an increase in the size of populations, leading to a potential increase in risk of transmission of T. cruzi to hosts if those specimens get infected. As found in earlier studies (Martínez-Ibarra et al. 2012a,b), the mortality of the youngest nymphs was mainly attributable to an incapacity to feed, because dead bugs generally lacked a significant intestinal content. By contrast, the mortality of the older nymphs occurred mainly during molting. There were no significant differences among the three populations in terms of percentages of females produced at the ends of their cycles. Thus, the three study populations had the same potential for increasing their abundance under favorable conditions, which could lead to an increased risk of transmission of T. cruzi to hosts in their distribution areas. The mean number of eggs laid per female per day was approximately three in the triatomines from Taretan, which might partially explain the abundance of M. pallidipennis in the state of Michoacán (Martínez-Ibarra et al. 2011) and their low abundance in Oaxaca (Benítez-Alva et al. 2012). Mexican triatomine species related to M. pallidipennis (i.e., M. mazzottii (Usinger, 1941) and M. phyllosomus (Burmeister, 1835) were investigated in a previous study (Martínez-Ibarra et al. 2006), as well as was T. infestans (Klug, 1834) (Rabinovich 1972), and like the current study, the egg eclosion rate was over 80% in the populations analyzed with average incubation periods of around 19 days, which demonstrated that the maintenance conditions were favorable to the proper development of these species of triatomines. Some of the study parameters led us to conclude that the three populations were different and they may have been affected by local environmental conditions. The correlation of our results with epidemiological and behavioral studies (Ramsey et al. 2003, Martínez-Ibarra et al. 2011) supports a hypothesis that biological traits are important criteria for determining the relationships among populations (Grech et al. 2010, Martínez-Ibarra et al. 2012a). Morphological and genetic studies of M. pallidipennis are necessary to understand more about the relationships among different populations of this species. We thank Diana Monserrat Martínez-Grant and Jorge Alejandro Martínez-Grant for their technical support.