SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH BIONOMICS STUDIES OF MANSONIA MOSQUITOES INHABITING THE PEAT SWAMP FOREST Chamnarn Apiwathnasorn1, Yudthana Samung1, Samrerng Prummongkol1, Achara Asavanich1, Narumon Komalamisra1 and Philip Mccall2 1Department of Medical Entomology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand; 2Liverpool School of Tropical Medicine, University of Liverpool,Liverpool, United Kingdom Abstract. The present study was conducted in the years 2000-2002 to determine the bionomics of Mansonia mosquitoes, vectors of nocturnally subperiodic Brugia malayi, inhabiting the peat swamp forest, “Phru Toh Daeng”, Narathiwat Province, Thailand. Fifty-four species of mosquitoes belonging to 12 genera were added, for the first time, to the list of animal fauna in the peat swamp forest. Mansonia mosquitoes were the most abundant (60-70%) by all collection methods and occurred throughout the year with a high biting density (10.5-57.8 bites per person-hour). Ma. bonneae was most prevalent (47.5%) and fed on a variety of animal hosts, including domestic cats, cows, mon- keys, and man with a maximum biting density of 24.3 bites per person-hour in October. The infec- tive bites were found for the first time in Ma. annulata collected at Ban Toh Daeng (13 00-14 00 hours) and also Ma. bonneae at forest shade (16 00-17 00 hours) and in a village (20 00-21 00 hours) with rates of 0.6, 1.1 and 1.0%, respectively.The biting activities of these two species oc- curred in both the day and night time, with two lower peaks at 10 00 hours (18.5 bites per person- hour) and 13 00-15 00 (8.5-10.0 bites per person-hour) hours, but the highest peak was 19 00-21 00 hours (31.5-33.0 bites per person-hour) The biting activity patterns corresponded with the peri- odicity found in man and domestic cats and may play an important role in either transmission or maintenance of the filarial parasites in the peat swamp forest. The relative role of Ma. bonneae and Ma. uniformis in different environmental settings (primary swamp forest and open swamp) on the transmission of nocturnally subperiodic B. malayi merits further study. INTRODUCTION differences in the strains of the parasites can affect mosquito susceptibility to infection Mosquito species of the genus Mansonia, (Edeson and Wilson, 1964). In spite of the epi- subgenus Mansonioides, are vectors of lym- demiological importance of Mansonia mosqui- phatic filariasis in Thailand. Six species in this toes in Narathiwat Province, few observations subgenus have been shown to be natural vec- have been carried out regarding their biono- tors of lymphatic filariasis (WHO, 1984). In Thai- mics, although data on biting densities has been land, Ma. bonneae, Ma. indiana and Ma. uni- collected by field workers from the Division of formis were firstly incriminated as vectors of Filariasis Control, Ministry of Public Health. brugian filariasis by Harinasuta et al (1970). Since Considerable information exists regarding filariasis transmission and epidemiology can be the bionomics of Thai mosquitoes (Iyengar and locally specific, vector ecology in different envi- Menon, 1956; Thurman, 1959, 1963; Bram, ronments should be investigated. Differences in 1967; Harrison and Scanlon, 1975; Huang, the species and strains of the mosquitoes and 1979; Gass et al, 1982), but little is known of the ecology of mosquitoes inhabiting peat Correspondence: Dr Chamnarn Apiwathnasorn, De- partment of Medical Entomology, Faculty of Tropical swamp forests. The peat swamp in Thailand is Medicine, Mahidol University, 420/6 Ratchawithi Road, estimated to occupy approximately 64,000 hec- Bangkok 10400, Thailand. tares (Phlengklai, 1989), of which 26,600 hec- Tel: 66 (0) 2354-9100-19 ext 1571: Fax: 66 (0) 2643- tares are in Narathiwat Province (Vijarnson and 5582 Pinichapong, 1987). Geographically, the study E-mail: [email protected] area was rather homogeneous, occupied by an 272 Vol 37 No. 2 March 2006 BIONOMICS OF MANSONIA INHABITING THE PEAT SWAMP FOREST extensive area of peat swamp forest with some as 8.25% (Ministry of Public Health, 1986). The variation in density of trees and vegetation. The average annual temperature is 27.6 ºC, with 77- average annual rainfall was 2,560 mm with 171 83% relative humidity, and an average annual rainy days; relative humidity and average tem- rainfall of 2,560 mm with 171 rainy days. The perature were 77-83% and 28ºC, respectively heaviest part of the rainy season, causing yearly (Phlengklai, 1989). flooding, is from November-December and the This study aimed to determine the mosquito driest period is from February-April. fauna of the peat swamp forest and the bio- Human biting and landing rates nomics of the vector species in relation to The collection stations were set at Ban Toh brugian filariasis, such as seasonal variation, bit- Daeng and Sirindhorn Research and Nature ing behavior, and vector incrimination. Study Center. Previously, the seasonal preva- lence of Mansonia mosquitoes was determined MATERIALS AND METHODS in the swamp-fringed areas in Khosit Subdistrict by the Division of Filariasis Control (Ministry of Study areas Public Health, 1999). This was used as a guide- The present study was carried out in a peat line to set an appropriate sampling period (April- swamp forest, Sirindhorn Research and Nature October) and time for the present study. Study Center located in Su-ngai Kolok District, Narathiwat Province, Thailand (6º 4’N, 101º 58’ Guptavanij et al (1973) reported that the E). In 1991, the Royal Forest Department de- ratio of outdoor/indoor collections of Mansonia clared approximately 50,000 acres (20,234 hect- mosquitoes in Narathiwat Province was 1.6:1, ares), or 66.8% of the total Phru Toh Daeng area, therefore, outdoor collections were performed as a wildlife conservation zone in honor of Her in the present study. To determine monthly den- Royal Highness Princess Maha Chakri sity of Mansonia species, mosquito collections Sirindhorn. The research center was established were conducted outdoors between 18 00-22 00 to be a field station for research study, and a hours for two consecutive nights per month at recreation place for people to learn and under- Ban Toh Daeng from April-October 2000. It was stand the peat swamp forest by observation not possible to extend the sampling period into along the study trail. Topographically, the peat the following year because of heavy flooding in swamp forest is low-lying flatland and year-round the collection sites. water logged. Rain-fed water drains out of the To determine mosquito biting cycles, hu- forest floor very slowly. The peat water is brown- man biting and landing counts were made hourly ish in color resulting from decomposition of tan- for 50 minutes for two groups, each with two nic substances disintegrated from dead plants persons, for three consecutive nights per month in water with a pH of 4.5-6.0. This peat swamp in September and October 2000. The captures forest has a high level of biodiversity with a re- were performed at 06 00-17 00 hours in the for- corded 470 plant species and 335 animal spe- est shade near the walking trail at the research cies, including birds (196), mammals (62), rep- center, and at 13 00-23 00 hours at Ban Toh tiles (50), amphibians (17), and rare animals (10). Daeng. The plant community is made up of large trees, Mosquito identification and dissection for shrubs, vines and various short-lived herbaceous filarial parasites were performed at a field labo- flora. There is no record of mosquito fauna and ratory at the Pikun Thong Development Study mosquito vectors inhabiting the peat swamp for- Center. All mosquito specimens were identified est. as to species using a standard dissecting mi- The selected village, Ban Toh Daeng, which croscope using taxonomic keys (Thurman, 1959; has a population of 129, is 1.5 km from the re- Wharton, 1962; Peyton and Scanlon, 1966; search center. In 1986, in the Annual Report of Bram, 1967; Harrison and Scanlon, 1975; the Division of Filariasis Control, the highest mi- Huang, 1979; Rattanarithikul, 1982). Dissection crofilarial infection rate in this region was reported for filarial parasites was performed on the head Vol 37 No. 2 March 2006 273 SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 60 10 and thorax portions of Mansonia mosquitoes as Average rainfall Ma. bonneae 9 described by Leemingsawat et al (1987). 50 Ma. annulata 8 Total Mansonia 7 40 RESULTS 6 30 5 Seasonal abundance of Mansonia sp 4 Rainfall (mm) 20 A total of 1,361 mosquitoes belonging to 3 2 19 species were collected at Ban Toh Daeng, of No. of mosquito bites/person-hour 10 which 1,192 were Mansonia mosquitoes: Ma. 1 0 0 annulata, Ma. annulifera, Ma. bonneae, Ma. Apr May Jun Jul Aug Sep Oct dives, Ma. indiana, and Ma. uniformis. The re- Month mainder were Aedes albopictus, Ae. caecus, Fig 1a Anopheles letifer, An. nigerrimus, Armigeres 14 10 Average rainfall subalbatus, Coquillettidia crassipes, Cq. 9 12 Ma. uniformis nigrosignata, Culex bitaeniorhynchus, Cx. Ma. indiana 8 Ma.dives 10 7 gelidus, Cx. pseudosinensis, Cx. sinensis, Cx. Total Mansonia tritaeniorhynchus, and Cx. vishnui. The most 6 8 abundant species was Ma. bonneae (47.5%) 5 6 followed by Ma. annulata (32.8%), Ma. uniformis 4 (9.8%), Ma. indiana (6.0%), and Ma. dives Rainfall (mm) 4 3 (3.9%). 2 No. of mosquito bite/person-hour 2 Wharton (1962) published a detailed study 1 of the biology of Mansonia mosquitoes in rela- 0 0 tion to filariasis in Malaysia. He reported that Ma. Apr May Jun Jul Aug Sep Oct Month annulata and Ma. bonneae bred in dense swamp Fig 1b forests where larvae were attached to the pneu- Fig 1–Monthly variation in man-biting rates (total no.