Nocturnal man biting habits of mosquito species in Serian, Sarawak, Malaysia ()
1. INTRODUCTION
Host feedings of mosquitoes are important implications for humans since it is by this activity that the biting rhythms of mosquitoes make an important contribution to determine periods of transmission risk and are also basic information for developing methods of personal protection against vector or nuisance mosquitoes.
A biomedical field study of the collaborative programme of the Institute Medical Research and Sabah State Health Department on research in tropical diseases was initiated in the Serian District, Sarawak. Serian, which is the main town in the district, is situated some 64 km from the state capital city of Kuching and is accessible by road transport. It is the focal point for villages situated in this area. Geographically, Serian District is a mountainous area with an equatorial climate which has conventional rain throughout the year. The wettest period is from November to February. The District is inhabited by a mixed number of ethnic groups of Land Dayak, Iban, Malays and Chinese. Their occupations varied with the majority of them being farmers living in villages in the interior of the District. The primary objective of the study was to determine the major mosquito fauna, in particular the vectors of malaria and filariasis. In the course of these studies, other mosquito species collected from Serian were also recorded. The species composition, biting activities and seasonal population dynamics of mosquitoes collected in the study sites were described. The study reported here was undertaken to consolidate and amplify information on distribution and abundance of mosquitoes in Serian district. These data are essential for planning programmes to alleviate health and nuisance problems caused by mosquitoes.
2. MATERIALS AND METHODS
The study was carried out in Balai Ringin, Serian District, Sarawak and was chosen based on 5 consecutive years of high malaria and filarial cases. The villages selected for the study have generally a low lying terrain with few hills and small swamps in between where dry padi and vegetables cultivations are also being practised. Field evaluations were conducted in six villages: Melikin Lama (N00˚58.833' E110˚47.525'), Simpang Melikin (N00˚59.834' E110˚48.007'), Danau Karangas Baru (N01˚00.161' E110˚47.803'), Danau Karangas Lama (N01˚00.313' E110˚47.878'), Danau Melikin (N00˚59.270' E110˚48.390') and Sungai Gudum (N00˚58.100' E110˚47.647'). The villages were chosen based on: high malaria and filaria incidence rate; high vector populations and village accessibility at all times of the year. However, most of these villages are in remote areas and accessible only by four-wheel drive vehicle.
Mosquitoes were caught indoors and outdoors using Human Landing Catching (HLC) technique. Twelve-hour mosquito collections were carried out bi-monthly, overnight from 7:00 pm to 7:00 am with two collectors each simultaneously stationed indoors and outdoors. All mosquitoes landing on human baits were caught using glass vials (50 × 19 mm), which were subsequently plugged with cotton. Two houses were selected for each village during two collection nights for each survey. All mosquitoes were identified using standard taxonomic keys [1,2] the following morning and segregated according to species, village and date. Identified female Anopheles mosquitoes were dissected to determine parity status of the ovaries. The midguts and salivary glands of parous mosquitoes were examined for malaria parasites using standard dissection techniques [3].
Data Analysis for Biological Parameters
Variation in adult mosquito densities between villages and months was compared using Friedman test. Mosquito density was expressed as number of mosquitoes collected per area and was calculated by totaling the mosquito density for all species in each sampling site. Comparisons of indoor and outdoor biting activities were analyzed by paired t-test and all data were analyzed using statistics software (SPSS 11.5 Production Facility).
3. RESULTS
Biting and feeding behavior of antrophophagic mosquitoes were studied in six villages in Balai Ringin, Serian District, Sarawak. Adult mosquito collections were performed for 36 nights during nine entomological surveys. Results are based on cumulative collection from all the study areas. A total of 213 Anophelines and 7059 Culicines were caught during the survey (Table 1). In this study, we detected the presence of four major species which included Ma. bonneae being the largest found in the area (23.8%), followed closely by two Culex species, Cx. vishnui at 22.3% and Cx. pseudovishnui at 19,6%, and lastly at 13.7% was Cx. tritaeniorhyncus.
We examined the species for every genus present and identified four Mansonia species with Ma. bonneae being the dominating species (92%) compared to the other species which contributed only a very small percentage: Ma. dives at 3.7%, followed by Ma. uniformis at 3.5% and finally Ma. annulata at 0.4%. We also captured nine species of Culex mosquitoes during the study. There were two dominating species, Cx. vishnui (30%) and Cx. pseudovishnui (28%). Other Culex species detected in the area were Cx. tritaenorhynchus (19%), Cx. Quinquefasciatus (13%) plus another five species which appeared in a very small percentage (between 1.8% - 0.02%) as follows: Cx. whitmorei, Cx. fuscocephala, Cx. Bitaeniorhynchus, Cx. gelidus, and Cx. hutchinsori. Aedes mosquitoes were also present in Balai Ringin. The species included Ae. albopictus, Ae. ceacus, and Ae. seatoi with Ae. albopictus being the dominant species detected at 83% followed by Ae. ceacus at 11% and Ae. seatoi at 6%.
As far as Anopheles mosquito is concerned, there were four Anopheles species present in the study area. The highest number of Anopheles species captured was An. letifer (90%). The other 10% were represented by three other species: An. separates (7.3%), An. tessalatus (1.8%), and An. argyropus (0.9%). All Anopheles mosquitoes were dissected for malaria parasites but no malaria infection was found in any of the vectors in the six study areas. Based on these findings we therefore listed species most heavily found in the study area based on individual genus as follows: An. letifer, Cx. vishnui, Cx. Peudovishnui, Ma. bonneae, Ar. durhami and Ae. allbopictus (Table 1). Friedman test indicated that significant differences did exist in mosquito collections across the villages [χ2(5, N = 27) = 32.109, p < 0.05]. Danau Karangas Lama (DKL) appears to be the site where highest number mosquitoes were collected during the study period.
Figure 1 demonstrated the number of species collected during each visit made to the area. Throughout the whole study period, nine visits were made to Balai Ringin, Serian, Sarawak. The most common species (detected in every visit) were Cx. vishnui, Cx. pseudovishnui and Ma. bonneae. Among these three species, Ma. bonneae presented a curve in terms of its monthly collection which was almost symmetrical with the highest peak that took place in Oct’08. As for Cx. pseudovishnui and Cx. Vishnui they too showed peaks which took place slightly earlier (Aug’08) than Ma. bonneae. Peak presented by Cx. pseudovishnui was almost two times higher than peak of Cx. vishnui. Cx. vishnui however produced a second peak which was almost two and a half times higher than its first peak during our final visit in Aug’09. A second peak
Table 1. Mosquito species trapped in Balai Ringin, Serian Sarawak.
Figure 1. Total number of adult mosquitoes collected per trip.
was also demonstrated by Ma. bonneae during that same visit but the peak was not as high as the first one and it was also lower than that of Cx. vishnui.
An. letifer was detected in seven out of our nine visits. They were not detected during our Apr’08 and Dec’08 visits. Although it was the most dominant species among the Anopheles mosquito, compared to species from other genus, their total number in those individual seven visits were considered very low (<50). As for Ae. albopictus and Ar. durhami, they were only detected once out of the nine visits. Ae. albopictus was detected in Aug’08 while Ar. durhami in Oct’08. Similar to An. letifer, the number of adults collected for both species was obviously very low compared to other species from other genus (Figure 1).
We then examined the number of adult mosquitoes collected outdoor and indoor for every visit made. The biting habit of Ma. bonneae within 12 hour period (dawn to dust) showed that this mosquito started biting around 7:00 pm and was very active and reached its highest peak at 8:00 pm. The biting activity began to drop drastically when approaching 9:00 pm and continued to drop further around 11:00 pm and then leveled off from 11:00 pm until 6 am. The biting activity of Ma. bonneae was found higher outdoor (110.333 ± 91.866) compared to indoor (33 ± 28.939) as shown in Figure 2.
Figure 3 shows the biting activity of Cx. vishnui indoor and outdoor. Cx. vishnui also started its biting activity after 7:00 pm for both indoor and outdoor. The outdoor activity was very active and reached its highest peak at 8:00 pm, while indoor activity took another two hours to reach its highest peak. At this point (10:00 pm), the outdoor activity dropped to its lowest level throughout the 12 hour period. From that point onwards, both