MEM INST OSWALDO CRUZ, RIO DE JANEIRO, 94(6) Nov/Dez 1999
PAGES: 715-718 DOI: Full paper
Role of Anopheles (Kerteszia) bellator as Malaria Vector in Southeastern Brazil (Diptera: Culicidae)

Oswaldo Paulo Forattini +, Iná Kakitani, Roseli La Corte dos Santos, Helene Mariko Ueno, Keilla Miki Kobayashi

Departamento de Epidemiologia, Núcleo de Pesquisa Taxonômica e Sistemática em Entomologia Médica, Faculdade de Saúde Pública, Universidade de São Paulo, Av. Dr. Arnaldo 715, 01246-904 São Paulo, SP, Brasil

Abstract

New research concerning Anopheles bellator in the southeast of the State of São Paulo, Brazil, are reported. Adult females of this mosquito showed remarkable endophily and endophagy which was even greater than An. cruzii. The epidemiological role of this anopheline as a malaria vector is discussed.

Among the Kerteszia subgenus of Ano-phelinae, Anopheles bellator has been considered as a vector of endemic malaria in southeastern Brazil. Despite the endemic situation at the present time declining to a low epidemiological level, the potential role of this vector has been a matter for assessment by investigations, particularly with respect to the anthropic environment represented by human dwellings in comparison to the sylvan behaviour of An. cruzii, another sympatric species of the same subgenus.

Early data regarding blood-seeking and general parity patterns have already been published (Forattini et al. 1993, 1996). According to these findings, despite there being no tendency towards resting within dwellings, both mosquitoes were present in man-made settlements. Even if the An. cruzii was more abundant, the local population of An. bellator showed greater endophagy, higher parity rates and maintained a greater abundance in natural environment.

To clarify the regional environmental influence and to confirm the behaviour of this population, new observations were planned and undertaken in the same region. The results obtained are presented and discussed below.

Study area - Adult catches were performed in the same study area as described elsewhere (Forattini et al. 1996). At the "Sítio Gentil" (Gentil Farm) mosquito collections were undertaken in the same previously mentioned house. This dwelling is located nearly 20 m, in a straight line, from the Atlantic Rain Forest which covers the regional Paratiu mountain slopes. To determine the influence of the estuary system hypothesis on An. bellator behaviour, a place near Pedrinhas village in the Ilha Comprida County covered by woody coastal lowland vegetation ("restinga"), situated nearly 4 km away from any house was chosen to perform catches.

With the objective of observing mosquito behaviour in a natural environment but contiguous to an urban center, the "Morro de São João" (Saint John's Hill) was selected. This hill is completely covered by Atlantic Rain Forest and is surrounded by Cananéia town, except on the seaward side.

 

MATERIALS AND METHODS

Biting activity was monitored fortnightly using two human bait collectors working simultaneously, one of them indoors and the other outdoors near the house. Mosquitoes landing on the host were collected with a hand-held aspirator. Landing collections began at sunset and continued for 2 hr. Due to seasonal variation, daily crepuscular data were obtained from the Nautical Almanac tables issued annually for local time. Mosquito collections started in May 1996 and continued until September 1997.

For purposes of comparison, other adult collections were undertaken in the natural environment with the use of a Shannon trap also operating fortnightly from 17:00 to 20:00 hr. At the "Sítio Gentil" forest, catches were carried out over the same period. In the Pedrinhas region, into the "restinga" (coastal lowland vegetation), collections were undertaken from May to September 1996. At Cananéia city, collections were made in the forest, on the "Morro de São João" during the evening hours 17:00-20:00 hr, starting in May 1996 and ending in August 1997.

The data obtained from all collections were analyzed statistically by the Man-Whitney test.

 

RESULTS

In the human dwelling environment the human bait yielded a total of 7,886 females of the two Kerteszia combined and including both indoor and outdoor catches. Among these mosquitoes, 2,546 were captured from inside the house and 5,340 were collected outside. The p value was 0.019 and therefore showed significance for the latter. Notwithstanding the results obtained for the two species, demonstrated the prevalence of An. bellator in the anthropic environment (Table I). The p values for the indoor and outdoor data were 0.009 and 0.004 respectively, verifying that as the differences observed between the two anopheline species were statistically significant.

Data on the collections made in the natural environments are presented in Tables II and III. In the "Sítio Gentil" slope forest, no significant differences were detected between An. cruzii and An. bellator as the value was 0.770. The same evidence was found in the Pedrinhas lowland vegetation with a value of 0.347. However, fewer collections were made there and this fact may have influenced the results. For Cananéia town (Morro de São João) the difference was significant (= 0.030), suggesting that An. cruzii was the most abundant species.

 

DISCUSSION

As is generally recognized in southeastern Brazil, the behaviour of the Kerteszia anopheline is essentially sylvan, particularly An. cruzii that specifically is charged with the maintenance of hypoendemic malaria in the Atlantic Rain Forest region of the State of São Paulo (Carvalho et al. 1988, Branquinho et al. 1997). However, another local species,An. bellator has not merited any special attention since the early observations of Rachou (1958). For this reason we undertook the present study, since earlier observations in the Ribeira Valley (Forattini et al. 1993) indicated that this mosquito to exhibited a degree of endophily and endophagy.

The degree of endophagy of An. bellator was found to be greater and to occur about four times more frequently in dwellings than that seen for An. cruzii. Therefore, from the epidemiological point of view, it fulfils at least one of the requirements to be considered as a malaria vector. Additionally, more than 30% of An. bellator females attracted to human bait are parous, i.e., seeking at least a second blood meal (Forattini et al. 1996).

The observations reported here confirm those previously published and mentioned above. Under natural environment conditions and depending upon the circunstances, both An. bellator and An. cruzii may occur in equal numbers. Data suggest that primitiveness, i.e., an undisturbed natural environment favours An. cruzii dominance. The results obtained from the catches at Pedrinhas may represent the true pattern because few collections were made there and included a monthly period with low adult production at the Shannon trap (Forattini et al. 1996). However, regarding the man-made surroundings, An. bellator seems to present a greater tendency to frequent dwellings. This synanthropic behaviour may reflect an ability to adapt to new environmental conditions resulting from man-made transformations, i. e., to the anthropic environment.

Another point that must be taken into account is the existence in the region of An. homunculus. This is necessary because it is morphologically closely related to An. cruzii and it has been hypothesized that this mosquito is a sibling species in a possible cruzii complex (Rosa-Freitas et al. 1998).

In conclusion, at least with respect to the population of the southeast of the State of São Paulo, An. bellator shows remarkable ecological and behavioural characteristics that could allow it to be considered as an epidemiologically important vector of malaria.

 

REFERENCES

Branquinho MS, Marrelli MT, Curado I, Natal D, Barata JM, Tubaki R, Carreri-Bruno GC, de Menezes RT, Kloetzel JK 1997. Infecção de Anopheles (Kerteszia) cruzii por Plasmodium vivax e Plasmodium vivax variante VK247 nos municípios de São Vicente e Juquitiba, São Paulo. Rev Panam Salud Pública 2: 189-193.

Carvalho ME, Glasser CM, Ciaravolo RMC, Etzel A, Santos LA, Ferreira CS 1988. Sorologia de malária vivax no foco Aldeia dos Índios, município de Peruibe, São Paulo, de 1984 a 1986. Cad Saúde Públ 4: 276-292.

Forattini OP, Kakitani I, Massad E, Gomes A de C 1993. Studies on mosquitoes (Diptera: Culicidae) and anthropic environment. 1 - Parity of blood seeking Anopheles (Kerteszia) in South-Eastern Brazil. Rev Saúde Pública 27: 1-8.

Forattini OP, Kakitani I, Massad E, Marucci D 1996. Studies on mosquitoes (Diptera: Culicidae) and anthropic environment. 11 - Biting activity and blood-seeking parity of Anopheles (Kerteszia) in South-Eastern Brazil. Rev Saúde Pública 30: 107-114.

Rachou RG 1958. Anofelinos do Brasil. Comportamento das espécies vetoras de malária. Rev Bras Malariol Doenças Trop 10: 145-181.

Rosa-Freitas MG, Lourenço-de-Oliveira R, Carvalho-Pinto CJ de, Flores-Mendoza C, Silva-do-Nascimento T 1998. Anopheline species complexes in Brazil. Current knowledge of those related to malaria transmission. Mem Inst Oswaldo Cruz 93: 651-655.

+Corresponding author. Fax: +55-11-282.1898. E-mail:  This e-mail address is being protected from spambots. You need JavaScript enabled to view it.
Received 15 April 1999
Accepted 24 June 1999

This work was supported by funds from the Fundação de Amparo à Pesquisa do Estado de São Paulo, grants 95/0381-4, 96/08991-9 and 96/09174-4, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Process 300225/95-4 and Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior.

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