Sand flies (Diptera: Psychodidae) in a cerrado area of the Maranhão state, Brazil

PUBLIC HEALTH

Sand flies (Diptera: Psychodidae) in a cerrado area of the Maranhão state, Brazil

Francinaldo S Silva^I; Luis P C de Carvalho^I; Francisco P Cardozo^I; Jorge L P Moraes^II; José M M Rebêlo^II

^IDepto de Biologia, Centro de Ciências Agrárias e Ambientais (CCAA), Univ Federal do Maranhão (UFMA), Rodovia MA 230 s/n,Campus IV, Bairro Boa Vista, Chapadinha, MA, Brasil

^IIDepto de Patologia, Lab de Entomologia e Vetores, Univ Federal do Maranhão, Praça Madre Deus nº 2, São Luís, MA, Brasil

ABSTRACT

The present paper aims to increase the knowledge on the sand fly fauna in the cerrado areas of Maranhão state in urban, rural and forest environments. The research was carried out from October 2007 to September 2008, between 18:00h and 06:00h, in the municipality of Chapadinha, northeast Maranhão. For insect sampling, CDC light traps were set up in peridomicile and domicile areas of urban and rural zones as well as in Cerrado and Gallery forests. The total of 1,401 specimens belonging to 17 species were sampled, all within the genus Lutzomyia. Lutzomyia longipalpis (Lutz & Neiva) (52.5%), Lu. evandroi (Costa Lima & Antunes) (18.3%), Lu. whitmani (Antunes & Coutinho) (12.1%), Lu. lenti (Mangabeira) (4.7%) and Lu. termitophila (Martins, Falcão & Silva) (4.0%) were the most frequently collected. From an epidemiological viewpoint, five from all of the collected species are vectors of leishmaniasis: Lu. longipalpis, Lu. whitmani, Lu. flaviscutellata (Mangabeira), Lu. gomezi (Nitzulescu) and Lu. chagasi (Costa Lima). Lutzomyia chagasi was registered for the first time in Maranhão state and Lu. saulensis (Floch & Abonnenc), Lu. monstruosa (Floch & Abonnenc) and Lu. gomezi were found for the first time in the eastern part of the state, since they had been reported only in the Amazonian region of Maranhão. Regarding to the studied environments, the urban chicken house had the highest number of specimens collected (801), while the Gallery Forest was the most diverse (15 species). This study demonstrates that the northeast cerrado exhibits a mixed sand fly fauna characterized by an extremely important species vectors assortment involved in the epidemiological cycle of leishmaniasis in Maranhão state.

Key words: Leishmaniasis, Lutzomyia, insect vector

Phlebotomine sand flies constitute a very important group of dipteran insects due to the species diversity and the association with leishmanial parasites throughout the world (Rangel & Lainson 2003). In Brazil, phlebotomine sand flies are well-known vectors of visceral and cutaneous leishmaniasis, with nearly 220 species identified from sylvatic and rural studies undertaken in several phytogeographic regions (Aguiar & Medeiros 2003). In the state of Maranhão, northeast Brazil, around 60 sand fly species have already been found by the National Health Foundation technical team in urban and rural peridomiciliary areas in more than 40 municipalities.

The wide-ranging and systematical studies included Amazonian humid forest, ombrophila forest and mixed vegetation composed of Cerrado, "Cocal" and Caatinga sites (Rebêlo et al 1999a, Rebêlo et al 2000a, Leonardo & Rebêlo 2004, Marinho et al 2008). However, studies focusing on the overall sand fly species diversity of the Cerrado biome in Maranhão state were only carried out in a restricted region, mostly at the municipality of Santa Quitéria (Martin & Rebêlo 2006) in the low Parnaiba River zone.

Therefore, because of the great importance of this transitional area for biodiversity studies in Maranhão state, this work proposes to survey the sand fly fauna associated with the sylvatic and anthropogenic environments as well as the species richness and their monthly and seasonal frequency, making a contribution to the understanding of the phlebotomine sand flies distribution and to the epidemiological profile of leishmaniasis in the state.

Material and Methods

Study area. The municipality of Chapadinha is situated between 3º 44'17" LS and 43º 20' 29'' LW and has a surface area of 3,265 km². The municipality has 60,646 inhabitants, where 23,427 reside in the rural zone and 37,219 live in the urban zone. Chapadinha municipality is situated in the Maranhão cerrado region, an area of 10 million ha accounting for 30% of the total state area, comprising 33 municipalities. It occupies a large transitional area positioned between three Brazilian regions: north, northern and central west. In the cerrado domain, several other distinct biomes can be found, such as "veredas", caatinga sites interfluvial mesophytic forest and gallery forest (Oliveira-Filho & Ratter 2002). The studied area is at approximately 100 m a.s.l. and the climate is hot and tropical sub-humid, with annual mean temperature ranging from 28ºC to 30ºC, with an annual mean precipitation between 1,600 mm and 2,000 mm. The region undergoes a 6-month dry season, from July to December, and a 6-month rainy season, from January to June.

The study areas were selected from urban and rural zones, as follow: a) urban zone: the collecting sites were represented by (i) a chicken house and (ii) banana trees, 36 m far from each other, in the peridomiciliary area, and (iii) a gallery forest fragment, belonging to the Reservatório Itamacaoca, an areaof the Companhia de Águas e Esgoto do Estado do Maranhão (CAEMA) of Chapadinha. The actual collecting point was situated at 926 m from the reservoir entry, adjacent to a nascent of the reservoir pond; b) rural zone: an area far 14.41 km from the municipality center which included the (iv) intradomicile, a (v) chicken roost and a (vi) pigsty. The rural chicken roost was less structured and often much more exposed than the urban one. The extradomicile environment was represented by (vii) a cerrado forest fragment next to the community.

Insect sampling. Phlebotomine sand flies were captured monthly from October 2007 to September 2008, between 18:00h and 06:00h, by means of CDC light traps. One trap was set up at 1.5 m from the ground in each collecting site, totaling seven light traps. Considering that each trap worked 12h a night and 12 months a year, the collecting effort yielded 144h/trap or, concerning the seven traps, 1,008 h/trap. After sampling, the insects were killed in ethyl acetate, stored in 70% ethanol, slide-mounted and identified to species according to Young & Duncan (1994).

Statistical analyses. The species richness was estimated by summing the number of species found in each collecting site. Sand fly diversity was estimated according to the Shannon-Wiener index by DivEs software 2.0 (Rodrigues 2005). For analyzing the species relative abundance and its confidence limits, the Kato et al method (Laroca 1995) was applied. One species was considered dominant when its lower confidence limit was inferior to the superior limit of the absent species. Constance of each species was determined with the formula: C = P x 100/N; where, P = number of collections with the considered species and, N = total number of collections. Thus, the species were classified as constant, accessory or accidental (Silveira Neto et al 1976).

Results

Richness and relative abundance. A total of 1,401 phlebotomine sand flies distributed in 17 Lutzomyia species were found, with Lutzomyia longipalpis (Lutz & Neiva) (52.5%), Lu. evandroi (Costa Lima & Antunes) (18.3%), Lu. whitmani (Antunes & Coutinho) (12.1%), Lu. lenti (Mangabeira) (4.7%) and Lu. termitophila (Martins, Falcão & Silva) (4.0%) being the prevailing species (Table 1). The remaining species accounted for 8.4% of the total sample. Females were predominant (60.7%) over males (39.3%), resulting in a 0.65: 1 male/female ratio. This tendency was observed for all species with the exception of Lu. whitmani and Lu. lenti, in which males prevailed over females (61.2% and 86.4, respectively). An extreme case was Lu. gomezi (Nitzulescu), in which only males were collected (Table 1). Specimens collected for Lu. sp 1 (group Aragaoi), Lu. sp 2 (subgenus unknown) and Lu. sp 3 (subgenus Psychodopygus) were insufficient for a correct identification and new samples are necessary for each one of these species.

The collecting effort revealed a capture rate of 1.4 individual per hour per trap. Phlebotomine sand flies were more frequent in the urban zone, where 75.0% of the specimens were captured. The urban chicken house was the most representative ecotope accounting for 58.6% of the total number of specimens sampled (Table 2), while 25.0% were captured in the rural zone.

The most abundant species, Lu. longipalpis, was predominant over the other species in the urban (chicken house: 63.8%; banana trees: 48.8%) and rural peridomiciliary environments (pigsty: 66.3%; chicken roost: 37.7%), as well as in the rural cerrado forest (39.2%). However, in the gallery forest, the prevailing species was Lu. saulensis (Floch & Abonnenc) (25.5%), while Lu. evandroi (41.9%) was the most common in the intradomicile.

The Shannon-Wiener diversity index was higher in the gallery forest, followed by the rural chicken roost. The lowest rates were found in the pigsty and in the urban chicken house (Table 2). The species richness was higher in the urban (15 species) than in the rural area (12 species). Among the species found in the urban areas, all of them were present in the gallery forest, where seven were exclusive for this environment, while eight were also recorded in the peri and intradomiciliary ecotopes. In the rural area, seven species were found in all collecting sites, with Lu. monstruosa (Floch & Abonnenc) and Lu. sordellii (Shannon & Del Ponte) being collected only in the intradomicile, while Lu. flaviscutellata (Mangabeira) and Lu. pilosa (Damasceno & Causey) were present only in the rural cerrado fragment (Table 2).

Monthly and seasonal distribution. Lutzomyia longipalpis, Lu. evandroi, Lu. termitophila, Lu. whitmani, Lu. lenti and Lu. trinidadensis (Newstead) were defined as constant species as they were sampled in more than 50% of collections. The accessory species, Lu. sordellii, Lutzomyia sp. 1 and Lu. saulensis occurred between 25% and 50% of the collections. The remaining species were considered accidental, as they were sampled in less than 25% of collections (Table 3).

Fourteen sand fly species were sampled in the rainy season while thirteen were captured in the dry season. Only ten species were present in both seasons. Lutzomyia borrouli (Barreto & Coutinho), Lu. chagasi (Costa Lima) and Lutzomyia sp. 2 were only found in the rainy season, while and Lu. gomezi, Lu. pilosa and Lutzomyia sp. 3 only in the dry season (Table 3). The relative abundance of individuals was higher in the rainy season, especially in May (64.2%) (Table 3). The most common species in the rainy season were Lu. longipalpis, Lu. evandroi, Lu. saulensis and Lu. sordellii.

Discussion

The species richness found in the cerrado region of Chapadinha was relatively high, comparable to that obtained from forested areas of the state capital São Luís (Marinho et al 2008) and from Buriticupu, Amazonian part of the state (Rebêlo et al 2000a,b) and higher from the average 10 species inventoried for other municipalities of Maranhão (Rebêlo et al 1999a,b), Araújo et al 2000, Barros et al 2000, Carvalho et al 2000, Martin & Rebêlo 2006).

Several species reported herein have already been found in other ecological areas of Maranhão. Lutzomyia saulensis, Lu. monstruosa and Lu. gomezi are poorly registered in the western Amazonian areas of the state (Rebêlo et al 2000a,b), being the presence of these species first recorded in the eastern section of Maranhão. These species also occur in other regions of the Brazilian legal Amazonia (Biancardi et al 1982, Castellón et al 1994). Lutzomyia saulensis was already reported to the cerrado region of Tocantins state (Andrade Filho et al 2001). Our report also extends the limits of distribution of Lu. chagasi to the far east of the Amazonian basin, including Maranhão. The remaining species are commonly found in the São Luís Island and in other eastern areas of Maranhão (Rebêlo et al 1999a, Martin & Rebêlo 2006, Marinho et al 2008).

Lutzomyia longipalpis was the most prevalent species occurring in all sampling sites all year round. This is a well adapted species to anthropogenic environments, vectoring Leishmania chagasi in several Brazilian regions (Soares & Turco 2003, Lainson & Rangel 2005, Nunes et al 2008), including Maranhão (Rebêlo et al 1999b, Martin & Rebêlo 2006).

The occurrence of Lu. whitmani in the peridomiciliary area shows that this species is highly adapted to human conditions, a fact already noted in other regions of Maranhão (Rebêlo et al 1999a,b, Martin & Rebêlo 2006, Leonardo & Rebêlo 2004). This vector has previously been found naturally infected with Leishmania species from the braziliensis complex, which is involved in the cutaneous leishmaniasis transmission in Maranhão (Oliveira-Pereira et al 2006), and in other Brazilian areas as well (Rangel & Lainson 2003, Costa et al 2007).

Although rarely trapped in most entomological inventories carried out in cutaneous leishmaniasis transmission areas in Maranhão, the low abundance of Lu. flaviscutellata should not be neglected, since this is a well known vector of Le. amazonensis, the causative agent of diffuse cutaneous leishmaniasis (Shaw et al 1972).

Two more species of medical interest concerned in leishmaniasis transmission were found: Lu. gomezi, incriminated in transmitting cutaneous leishmaniasis in Equador, Panama and Venezuela (Jorquera et al 2005, Sharma & Singh 2008), and Lu. chagasi, implicated in the transmission cycle of Le. braziliensis complex in the Amazonian region (see Rangel & Lainson 2003).

The role of chicken houses in attracting and maintaining sand fly populations has been discussed (Alexander et al 2002), possibly indicating that these artificial shelters may be an important reservoir of visceral leishmaniasis focus in human surroundings. Chicken rearing is a very common activity among the inhabitants of Maranhão (Dias et al 2003) and the presence of animals in the peridomicile, along with other environmental elements, is thought to be a risk factor for visceral leishmaniasis transmission (Moreno et al 2005). The forest area in which a light trap was set up for capturing sand flies presents environmental aspects of gallery forest. It is known that Amazonian and Atlantic gallery forests can be found along the humid valleys in the cerrado biome, and this feature may explain the phlebotomine sand fly fauna and the diversity values found for those environments. The physiognomic characteristics found in the gallery forest seem to work as a refuge for the sand fly species commonly found only in humid forests such as Lu. gomezi and Lu. saulensis (Castellón et al 1994, Rebêlo et al 2000b).

The seasonal profile of phlebotomine sand flies depicted herein corroborates other inventories carried out in Maranhão, where a great amount of individuals have constantly been trapped in the rainy season. The annual occurrence of Lu. longipalpis suggests that the visceral leishmaniasis transmission is not dependent on the rainy period, even though an increased sand fly population has been collected during the highest pluviometric index season, as previously reported (Rebêlo et al 1999b, Carvalho et al 2000, Araújo et al 2000). Lutzomyia whitmani occurred almost all year round and mostly in the rainy season, as already observed in cerrado region (Rebêlo et al 1999b) and in the Amazonian areas of Maranhão (Rebêlo et al 2001).

This work contributes for a better understanding of the phlebotomine species occurring in Maranhão, mainly in the northeastern cerrado domain, for which new records of sand fly species distribution were presented. The finding of potential vectors of Leishmania parasites in Chapadinha also raises the possibility that autochthonous cases of leishmaniasis may have already been in place.

Acknowledgments

We would like to acknowledge Rosa Maria Marques and Stephane Silva Sousa for allowing insect samplings at their houses. We also thank the support of Secretaria de Estado da Saúde de Chapadinha for the loan of light traps.

Received 01/VI/09.

Accepted 16/VI/10.

Edited by Neusa Hamada - INPA

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Publication Dates

• Publication in this collection
  17 Jan 2011
• Date of issue
  Dec 2010

History

• Received
  01 June 2009
• Accepted
  16 June 2010