Cytogenetic study of Anopheles albitarsis (Diptera: Culicidae) by C-banding and in situ hybridization.

The C-banding pattern and the size and location of the nucleolar organizer regions (NORs) are described for the first time in Brazilian populations of Anopheles (Nyssorhynchus) albitarsis sensu lato. C-banding revealed variation in the size of the centromeric heterochromatic blocks in autosomal chromosomes and in the acrocentric (X) and puntiform (Y) sex chromosomes. Fluorescence in situ hybridization showed that the NORs were located in the pericentromeric region of the sex (XX/XY) chromosomes and that this coincided with the number and location of centromeric constitutive heterochromatin blocks previously revealed by C-banding. The NORs varied in size among the homologues of the three populations. These findings of the populations studied support the hypothesis that the stability of NORs in the A. albitarsis complex is characterized by the presence of clustered and conserved sites in a unique pair of chromosomes.

Karyotype of Brazilian Anopheles albitarsis sensu lato (Diptera: Culicidae)

Anopheles (Nyssorhynchus) albitarsis sensu lato is an important malaria vector in Brazil, especially in the Brazilian Amazon region. Chromosome preparations of fourth-instar larvae of A. albitarsis from Iranduba and Coari (AM) and Ilha Comprida (SP) were analyzed for karyotype determination and to improve cytogenetic identification of this species. Anopheles albitarsis possesses 2n = 6 chromosomes, with two pairs (submetacentric and metacentric) of autosomes and one pair of sex chromosomes, with X-Y dimorphism. The sex pair is homomorphic and acrocentric in females and heteromorphic in males, with a punctiform Y chromosome. Somatic pairing was detected in the prometaphase and metaphase chromosomes of the three A. albitarsis populations. Apparently, sex chromosome evolution in the Culicidae does not function as does evolution in the Culicidae, since it occurs in the subfamily Anophelinae, which possesses heteromorphic sex chromosomes and is regarded as primitive, based on several criteria. These karyotype data on the albitarsis complex reinforce the hypothesis that sex chromosome evolution in the subfamily Anophelinae is conserved, and the variation revealed in the mean size of chromosomes in three populations indicates that selective pressure in these populations is occurring only at a genetic level.

Vector competence of rural and urban strains of Aedes (Stegomyia) albopictus (Diptera: Culicidae) from São Paulo State, Brazil for IC, ID, and IF subtypes of Venezuelan equine encephalitis virus.

Aedes albopictus (Skuse) is an Asiatic mosquito species that has spread and colonized all continents except Antarctica. It has major public health importance because it is a potential vector of several pathogens. The objectives of our study were to analyze the vector competence of urban and rural strains of Ae. albopictus from São Paulo State (Brazil) for Venezuelan equine encephalitis virus (VEE) subtypes IC, ID, and IF, and to evaluate the effect of infection with subtype IC of VEE on mosquito longevity. Both mosquito strains were susceptible to subtypes IC and ID, but the infection rate for subtype IF was low. Infection and transmission rates of Ae. albopictus for subtype IC were similar to those reported for Ochlerotatus taeniorhynchus (Wiedemann). The high infection, dissemination, and transmission rates for subtype ID reported for Oc. fulvus (Wiedemann) and Culex (Melanoconion) spp. are comparable with those found in this study. We found significant differences in the susceptibility to subtype IC between rural and urban populations of São Paulo. Significant survival rate differences were observed between uninfected and infected mosquitoes, but there were no differences in survival between rural and urban mosquito strains.

[Emergence of Aedes albopictus in artificial containers]. / Emergência de Aedes albopictus em recipientes artificiais.

OBJECTIVE: To estimate the potential of daily average emergence of Aedes albopictus adult females. Since this species is very close to Aedes aegypti, although it has not been implicated in the spread of dengue in Brazil. METHODS: Observations were carried out fortnightly and incessantly in Pedrinhas, in the state of São Paulo, Brazil, between 1996 and 2000. Breeding productivity was measured using the emergence index (E). Two large reservoirs of more than 10 liters of water were used, and their permanent character was assured by replacing water every time its level was low. The other reservoirs were six pots, initially filled out with a liter of distilled water. The water content was constantly replaced after every collection, regardless of rainfall. The associations with climatic factors were calculated using the correlation index of Pearson. RESULTS: The emergence (E) in the uncovered reservoir was 66.5, much higher than the one found at the covered water tank, which was 12.2. The permanent character of both breeding settings was assured by water replacement when there was a decrease in the water levels. There was no significant association between rainfall and temperature variations. It was observed in some of the six pots an association between rainfall and the emergence index, with a lesser productivity in the months with lower rainfalls. That period, June to November, would be the most propitious time to perform the mechanical removal of the containers. CONCLUSION: The differences in productivity of the two permanent reservoirs could be explained, at least in part, to the existence of organic matter that allows larval growth. Regarding the temporary containers, it seems that the best time for cleaning up would be during the dry months. Having organic matter in the water of breeding settings could enable the isolation of these two mosquito populations, Aedes aegypti and Aedes albopictus.

Description of immature stages of Culex ocossa Dyar & Knab, Culex delpontei Duret and Culex pereyrai Duret of the Melanoconion subgenus (Diptera: Culicidae).

The larva and pupa of Culex (Melanoconion) ocossa Dyar & Knab are redescribed and those of Culex (Melanoconion) delpontei Duret and Culex (Melanoconion) pereyrai Duret are described from specimens collected in the states of São Paulo and Paraná, Brazil. The pupa of Cx. ocossa differs from those of the other two species in having seta 5-IV-VI dark with strongly aciculated branches, and caudolateral angle of segment VIII produced into sharp point, and seta 1-P present; Cx. delpontei can be distinguished from Cx. pereyrai in possessing paddle lightly tanned, trumpet flared, and wing and leg cases lightly tanned, without pattern of dark spots; Cx. pereyrai can be recognized by having wing case with pattern of dark, discontinuously pigmented, longitudinal lines, and trumpet cylindrical, not flared. The larvae of the three species share the presence of seta 2-C placed medially to seta 1-C.

[Aedes albopictus in bromeliads of anthropic environment in São Paulo State, Brazil]. / Aedes albopictus em bromélias de ambiente antrópico no Estado de São Paulo, Brasil.

OBJECTIVE: Aedes albopictus populations can breed in several kinds of containers, and its presence has also been reported in Bromeliaceae. The purpose of this study was to evaluate the epidemiological importance of the Bromeliaceae plants as potential breeding sites of Aedes albopictus and to document the associated Culicidae entomofauna found in this micro-habitat. METHODS: Collections of Culicidae larvae were carried out fortnightly in aquatic content of bromeliads during 1998 and 1999. Collections took place in urban and periurban areas of Ilhabela island and periurban area of Ilha Comprida island, Brazil. RESULTS: A total of 26,647 Culicidae larvae were collected at both study sites, 14,575 in the urban area and 10,987 in the periurban area of Ilhabela and the remaining 1,085 in the periurban area of Ilha Comprida. There was no statistical difference between the amount of larvae collected in urban and periurban areas of Ilhabela. Regarding the Ae. albopictus, there was found a higher frequency and amount of larvae in the urban area of Ilhabela, followed by the periurban area in the same site, whereas in the periurban area of Ilha Comprida, its presence was considered accidental, since it was reported only in the first three months. CONCLUSIONS: The results show that bromeliads, largely used in landscaping, may contribute to the spread of Ae. albopictus. The presence of this species in domesticated and domiciled bromeliads allows us to suggest that the Culicidae larva is part of the regional fauna and facilitate the contact between humans and etiological agents of the natural ecosystem.

[Adult Aedes albopictus and Ae. scapularis behavior (Diptera: Culicidae in Southeastern Brazil]. / Comportamento de Aedes albopictus e de Ae. scapularis adultos (Diptera: Culicidae) no Sudeste do Brasil.

OBJECTIVE: Aedes albopictus and Ae. scapularis were found living together in the Pedrinhas Village, Southeastern of São Paulo State, Brazil. This finding was a good opportunity to make observations about the mosquitoes' behavior. METHODS: From October 1996 to January 2000 observations were carried out through systematic collections with human bait, environment aspirations and Shannon trap utilization. Synanthropy was estimated by the Nuorteva index and synanthropic ratios. RESULTS: The 87 collections with human bait yield 872 females adults. Williams' means, multiplied by 100, were 118 and 21 for Ae. albopictus at the 7 AM-6PM and 6PM-8PM hours, respectively, 100 and 106 for Ae. scapularis at the same timetable but there was an evening peak. Through environmental aspirations, a total of 1,124 adults samples was collected, 226 Ae. albopictus samples and 898 Ae. scapularis samples. The period between the months of January-May was the one with higher yield for both mosquitoes. There was no Ae. albopictus in the Shannon trap operated inside the adjacent forest. Regarding the sinanthropy, that culicid showed the higher index values, while Ae. scapularis was ubiquitous. CONCLUSIONS: The data obtained allows to form the hypothesis that Ae. scapularis females may have a diapause phase in the resting places and after that period they will retake the hematophagy habit. That might explain the higher activity at the human bait during the dry months, corresponding to the period of July-October.

[Finding of Aedes aegypti breeding in bromeliad]. / Nota sobre o encontro de Aedes aegypti em bromélias.

A breeding place of Aedes aegypti immature forms were found in bromeliads domesticated for decorative purposes. Implications for the control measures were considered.

Redescription of the adult and larva and first description of the pupa of Anopheles (Kerteszia) laneanus.

Anopheles (Kerteszia) laneanus is redescribed and compared with other species of the subgenus Kerteszia. The pupal stage is described for the 1st time and information on bionomics is provided.

[Parity and ovarian development of Anopheles albitarsis l.s.in irrigated agroecosystem field]. / Paridade e desenvolvimento ovariano de Anopheles albitarsis l.s. em área de agroecossistema irrigado.

INTRODUCTION: To determine the parity, ovarian development and survival rates of Anopheles albitarsis species, in order to estimate the potential of malaria transmission. METHODS: Two populations of Anopheles albitarsis A and B in an Experimental Farm of S. Paulo State, Brazil were captured during the crepuscular sunset, between 5PM and 8PM, using Shannon traps. Dissections were performed using Polovodova's technique, and the evaluation of follicular development was according to Christophers and Mer's criterion. The Vercruysse method was used to estimate daily survival and we applied Davidson method to determine the duration of the gonotrophic cycle. RESULTS: A total of 2,612 specimens was dissected, of these, 237 of population A and 2,375 of population B. The daily survival rates were 0.5339+/-0.047 and 0.5566+/-0.015, respectively, for the populations A and B. The duration of the gonotrophic cycle for population A was 1,990 days and for population B 2,046 days. CONCLUSIONS: The results help to estimate the malaria transmission potential in the region.

[The synanthropic potential of Kerteszia and Culex mosquitoes (Diptera:Culicidae) in Southeastern Brazil]. / Potencial sinantrópico de mosquitos Kerteszia e Culex (Diptera: Culicidae) no Sudeste do Brasil.

OBJECTIVE: To determine the synanthropic potential of Anopheles bellator and An. cruzii in a village close to a wild environment. For comparative purposes, Culex quinquefasciatus and Cx. sacchettae populations were also investigated. METHODS: From October 1996 to January 2000, vectors investigations were carried out in Pedrinhas village, Southeastern of S. Paulo State, Brazil, through systematic collections with human bait, air aspirations and Shannon traps. The synanthropic index was estimated using Nuorteva's indices plus the Mihályi's endophylic factor. RESULTS: Attraction principle was s=35.7 for both Kerteszia species at the peridomiciliary environment through human bait. Cx. sacchettae showed a sr ratio of 12.8 with a degree of synanthropy. However active search through the aspiration method yielded negative s values, such as -43.1 for An. bellator and -48.2 for An. cruzii. For Cx. sacchettae that value was -3.0. These values were calculated when +100.00 was given to Cx. quinquefasciatus, which showed the highest synanthropic habits, corresponding to s =+93.8. CONCLUSIONS: The present data allow to conclude that what was observed until now for isolated rural dwellings is valid for small villages at the same conditions. This means that female Kerteszia adults tend to be in anthropic environment for blood seeking. After that, they return to the surrounding natural environment of the village. Regarding Cx. Sacchettae, they seem to have an anthropic adaptation tendency.

Role of Anopheles (Kerteszia) bellator as malaria vector in southeastern Brazil (Diptera: Culicidae).

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.

[Marking-release-recapture methods for determining the size of the natural population of Anopheles albitarsis l.s (Diptera:Culicidae)]. / Marcação-soltura-recaptura para determinar o tamanho da população natural de Anopheles albitarsis l.s. (Diptera: Culicidae).

OBJECTIVE: In order to evaluate the size of the Anopheles albitarsis s.l. population in the Ribeira Valley region of the south-eastern S. Paulo State, Brazil, marking-release-recapture experiments were carried out on the Experimental Farm in Pariquera-Açu county where an artificial irrigation system for the cultivation of rice has been installed. The experiments aimed at determining the vectorial capacity of this species. METHODS: During the summer (January, February and March), three marking-release-recapture experiments with field and laboratory reared populations were conducted to evaluate the population size. Simultaneous human bait collections were also carried out to estimate the human biting rate. RESULTS: The population sizes of the three experiments were estimated to be 64,560, 50,503 and 22,684 mosquitoes. The bite/man/night rate varied from 41.5 to 524,5. DISCUSSION: The results indicated high mosquito density in the summer which allow one to infer that, even though the survival rate is low, the number of remaining females is large enough to outlive the parasite's extrinsic developmental period.