Prior to 1965, Singapore was part of the Malaya (now Malaysia) and was usually not mentioned when mosquito records were reported for Malaya. Consequently, many species that occurred in Singapore were not listed in the world mosquito catalog, and the available checklist for Singapore since 1986 is incomplete, with some imprecise species information. In updating this checklist, we examined and verified mosquito specimens collected from Singapore in various depositories, including a thorough review of past taxonomic literature. Here, we report a checklist of 182 mosquito species, 33 new distribution records, and a consolidated status list of vectors for Singapore. As Singapore is a travel hub and hosts one of the busiest container ports in the world, there is a risk of introducing mosquito species and their associated pathogens of human disease to the country. Hence, the distribution records are important to increase our knowledge on mosquito ecology as well as to understand the risk of newly introduced vectors and their associated pathogens.
Singapore is located 137 km north of the equator (1.28° N, 103.83° E) and about 1.6 km south of Peninsular Malaysia across the Straits of Johor. As a tropical country, Singapore has year-round hot and humid conditions with an average temperature of 27.5°C, mean daily relative humidity of 83.9%, and mean annual rainfall of 232.9 cm (Metereological Services Singapore 2017). Much of Singapore is covered with greenery (56%), which includes nature reserves, urban parks, mangroves, and adventitious vegetation (Yee et al. 2011). These, together with human-made habitats in urban areas, provide an ideal environment for inhabitation by diverse mosquito species (Colless 1957a, Laird 1988).
More than 3,500 species of mosquitoes have been described globally (Harbach 2018, Walter Reed Biosystematics Unit 2018) and at least 871 species are present in Southeast Asia. In Singapore, much of the earlier work on mosquitoes was carried out by a few prominent taxonomists from the 1920s to 1960s (Edwards 1926; Edwards and Given 1928; Reid 1950, 1968; Colless 1957a,b, 1958, 1965; Mattingly 1959, 1965). During this period, species collected in Singapore were often recorded under Malaya, which included contemporary Singapore and Malaysia. Consequently, many species that occurred in Singapore were not listed under Singapore in the world catalogs of mosquitoes (Stone et al. 1959, Knight and Stone 1977). Apiwathnasorn (1986) listed species in 11 Southeast Asian countries (including 126 species in Singapore); however, the list was incomplete and included some imprecise information. Recent sampling efforts on mainland Singapore and surrounding islands had contributed additional records and increased the number of recorded species to 140 in 2012 (Jeffery et al. 2010, Lee et al. 2012). These included three species, Culex (Culiciomyia) fragilis Ludlow, Lutzia (Metalutzia) halifaxii (Theobald), Lutzia (Mlt.) vorax Edwards, which were recorded in the checklist for Ubin Island, but not indicated as new records at that time (Lee et al. 2012). In recent years, considerable advances have been made in mosquito taxonomy, including taxonomic revisions, publication of keys, and new species descriptions (Rattanarithikul et al. 2005, 2006a,b, 2007, 2010), and in molecular tools, such as DNA barcoding (Linton et al. 2005). All of these have aided in species delineation and have improved the accuracy of mosquito identification (Chan et al. 2014).
Historically, Singapore not only has held a significant place in the recognition and documentation of the diversity of mosquitoes, but also the training of many mosquito taxonomists and medical entomologists in the Malay Archipelago, including D. H. Colless, J. A. Reid, and A. A. Sandosham. Much of our knowledge of the taxonomy of mosquitoes and the various pathogens of human diseases they transmit in Southeast Asia come from the works of these scientists. Although considerable efforts have been expended by taxonomists to define the mosquito fauna in Singapore, a comprehensive checklist of vector and nonvector species has never been accrued and published. To show that a species is a vector of pathogens of human diseases, it is necessary to demonstrate all of the following: 1) an association in space and time between species of mosquitoes and cases of disease in humans, 2) evidence of direct contact between the mosquito species and humans through landing/biting catches, 3) evidence that the species collected under natural conditions harbors the pathogen in its infective stage, and 4) proof of efficient transmission of the pathogen in laboratory conditions (Beier 2002, Eldridge and Edman 2012, Wilson et al. 2017). However, it is often difficult to obtain all necessary evidence and many species incriminated in the past were based on inferences and indirect evidence.
Singapore is a travel hub and hosts one of the busiest container ports in the world. Consequently, there is a risk of introducing mosquito species and their associated disease-causing pathogens into the country (Institute of Medicine 2010, Heng 2015). The occurrence records of mosquitoes are important not only to enhance our knowledge of mosquito systematics, but also to assess the risk of associated vector-borne disease agents (Hutchings et al. 2016). Our objectives in this paper are to: 1) present an annotated and updated checklist of mosquito species in Singapore with detailed taxonomic notes, 2) document new distribution records from Singapore, 3) rectify erroneous past species records, and 4) provide a consolidated vector status list.
Materials and Methods
We examined and verified mosquito specimens collected from Singapore in various depositories and thoroughly reviewed past taxonomic literature. Specimens deposited by past collectors were first examined in two local depositories, Environmental Health Institute of National Environment Agency (EHI) and Lee Kong Chian Natural History Museum (LKCNHM), and the checklist was then supplemented by verifying the collections in foreign depositories, such as the National Museum of Natural History (NMNH) in Washington D.C., the Natural History Museum (NHM) in London, and the Muzium Zoologi Universiti Malaya (MZUM) of the Universiti Malaya (UM) in Kuala Lumpur. Whenever necessary, anatomical characters of the male genitalia were examined to confirm the identification.
Among the local depositories, EHI has amassed the larger mosquito collection of over 7,000 pinned adult specimens and 1,600 larval specimens, belonging to more than 100 species collected from mainland Singapore and a few off-shore islands. The collection dates back to the 1970s when mosquito surveillance was conducted as part of the national-integrated vector control program. It was initially carried out by the Vector Control and Research Department until 2002, when the National Environment Agency and its public health laboratory, EHI, was founded and continued the collection.
The collection represents specimens collected from different habitat types across multiple locations using a range of methods. Larvae were collected from aquatic habitats using standard larval dippers (350 ml, 13 cm diameter; BioQuip, Rancho Dominguez, CA) and plastic pipettes, and locality details were recorded. The larvae were preserved at the larval stage or individually reared to adults, which were preserved as morphological voucher specimens along with their associated larval and pupal exuviae. Adults were collected using traps, including modified CDC Light Traps (CDC-LT; U.S. Centers for Disease Control and Prevention) baited with dry ice, BG-Sentinel traps (Biogents AG, Germany) and Gravitraps (EHI, Singapore). In some military-restricted areas, adults are collected by human landing catch by the Singapore Armed Forces. GPS coordinates were obtained using Garmin handheld devices (Garmin Ltd., USA) or from Google Maps, and expressed in degrees, minutes, and seconds format.
In addition to examining specimens, past taxonomic literature and catalogs (Stone et al. 1959, Knight and Stone 1977, Apiwathnasorn 1986, Townsend et al. 1990) that reported species from Singapore were also crosschecked and reviewed to rectify inaccurate species records and other records that were overlooked. We reviewed over 100 published references (Notes) and provide explanations for the exclusion or inclusion of species, as well as useful taxonomical remarks. To prepare the vector list, we reviewed literature on vector species and their associated diseases in Singapore and neighboring countries (Malaysia, southern Thailand, Indonesia, and Brunei Darussalam).
Results
Mosquito Species Diversity
This study represents the first comprehensive list of mosquitoes from Singapore, including 182 species in subfamilies Anophelinae and Culicinae, based on confirmed records and verified specimens (Table 1). Ten out of the 11 tribes of subfamily Culicinae are reported here (Harbach and Kitching 1998) and of these, 20 genera and 43 subgenera are represented (Wilkerson et al. 2015) (Fig. 1). Culex has the highest number of species (46), followed by Aedes (37) and Anopheles (21) (Fig. 1).
In our updated checklist, 42 species are added (Notes), and 10 species erroneously reported in the older publications are removed (Excluded Species). Among the 182 species listed, 33 new species records with ecological information (Table 2) are reported for the first time. Other new taxonomic records include two genera (Hodgesia and Udaya) and five subgenera, Ae. (Edwardsaedes), Ae. (Finlaya), Ae. (Phagomyia), Cx. (Acalleomyia), and Verrallina (Harbachius).
Among the new records, 21 species were only found in forested areas, 11 species in both forested and urban areas, and one species, Verrallina (Har.) consonensis (Reinert), only in urban areas. In forested areas, the highest number of new species recorded was from Tekong Island (12 species), an offshore island comprising secondary forests, coastal forests, and reclaimed land. This is followed by Bukit Timah (seven species) and Sungei Buloh Wetland Reserve (five species) (Fig. 2), which are areas with primary and mature secondary forests, and mangroves, respectively.
Mosquitoes of Public Health Importance
About 25 mosquito species are known vectors or potential vectors of human disease-causing pathogens in neighboring countries and Singapore (Table 3). Of these, nine are recognized as vectors in Singapore (Table 3). Some of the indicated vector species do not have available natural infection information or published records, but are still included in the list based on past studies. The remaining 16 species are listed as potential vectors in Singapore based on inference from field evidence (Anopheles kochi Dönitz), laboratory susceptibility tests on local species strains (Aedes malayensis), and vector records in neighboring countries (14 species).
Discussion
Mosquito Species Diversity
Our study provides a comprehensive review of the historical literature and confirmation of species that have been recorded from Singapore. The 182 species reported here represent a broad spectrum of culicid taxa from the two subfamilies, Anophelinae and Culicinae. There are 24 recorded genera in Southeast Asia, of which 20 are present in Singapore (Walter Reed Biosystematics Unit 2018). This suggests that the diversity of mosquitoes in Singapore is fairly well represented across the Culicidae (Harbach 2007). The four genera which are not present in Singapore (Bironella, Culiseta, Kimia, and Topomyia) have been recorded in Malaysia and Indonesia, the two countries flanking Singapore geographically. These data highlight the importance of Singapore's mosquito research efforts because of its geographical position between Peninsular Malaysia to the north and the partially different mosquito fauna in the nearby Indonesian islands of Java and Sumatra to the south. This will advance our understanding of the biogeographical distribution of the mosquito fauna in Southeast Asia.
The high number of new records found in Tekong Island (12 species) may be in part due to the broad range of habitats present in its coastal and forested areas, and the regular mosquito surveillance program in place (Lee et al. 2010). Nonetheless, infrequent collections from forested areas in Bukit Timah, Sungei Buloh, and Mandai have resulted in new records of seven, five, and four species, respectively. It is likely that the mosquito fauna in those areas is under sampled, and more extensive sampling activities may yield additional species records.
During the preparation of this checklist, the identifications of several genus groups such as Cx. (Lophoceraomyia), Ae. (Downsiomyia), Verrallina, Hodgesia, and Tripteroides remained unresolved. They require further collection and examination of more specimens to describe larval and male genitalia morphology and utilization of molecular techniques to resolve some taxonomic problems in these groups.
While carrying out a complete literature review, we found a few species records that were erroneously included or excluded in previous checklists. This was partly due to many authors using the term ‘Malaya’ to encompass both Peninsular Malaysia and Singapore in many publications prior to Singapore's independence in 1965. After Singapore's independence, many of the species records listed under Malaya were not corroborated and were either excluded from Singapore or included erroneously (Notes and Excluded Species). In addition, several cryptic and morphologically similar species were misidentified, resulting in the incorrect reporting of their distributions (Notes and Excluded Species).
Mosquitoes of Public Health Importance
In Singapore, important arboviral diseases include dengue, chikungunya, Zika, and Japanese encephalitis (Table 3). Aedes aegypti is the primary vector of dengue in Singapore, whereas Ae. albopictus is a secondary vector (Chung and Pang 2002, Lee et al. 2013). Both species are also involved in the local transmission of chikungunya and Zika viruses (Ng et al. 2009, Tan et al. 2017, Ho et al. 2017). Mendenhall et al. (2017) reported that Ae. malayensis showed high susceptibility to dengue and chikungunya viruses and should be considered a potential vector. Through studies conducted in the 1960s, three malaria vectors have been identified in Singapore—Anopheles maculatus Theobald, Anopheles epiroticus Linton and Harbach, and Anopheles letifer Sandosham (Chan 1969, Chan et al. 1976, Goh 1983). Anopheles sinensis, an important malaria vector in China and South Korea (Rueda et al. 2005), was the predominant species in two localities (Mandai-Sungei Kadut and Sembawang) where local transmission of Plasmodium vivax was detected in 2009 (Ng et al. 2010). All dissected adults of An. sinensis and other Anopheles species, however, were found to be negative for sporozoites and oocysts. Nevertheless, recent infection experiments using blood from infected patients showed that An. sinensis is susceptible to P. vivax infection (Pang et al. 2017), thus implicating its role in earlier transmission (Ng et al. 2010).
Although transmission of Plasmodium knowlesi has been reported in Singapore (Ng et al. 2008), the vector has not been determined (Wong et al. 2011). Routine mosquito surveillance carried out in the affected areas found six species of Anopheles, including An. kochi Dönitz. It was suggested that An. kochi might be a potential vector as previous laboratory studies have shown it to be susceptible to P. knowlesi (Coatney et al. 1971). Species belonging to the An. leucosphyrus group have been incriminated as vectors of P. knowlesi (Wharton and Eyles 1961; Vythilingam et al. 2006, 2008; Tan et al. 2008). They were previously reported from Singapore (Colless 1956, Chew 1968), but have not been found since 1969, despite evidence of P. knowlesi transmission in Singapore (Ng et al. 2008). This could be due to the lack of sampling in the canopy as their natural monkey hosts are arboreal in nature (Faust and Dobson 2015). Hence, further epidemiological and entomological surveillance (including canopy sampling) needs to be done to incriminate the vector species for P. knowlesi in Singapore.
Fig. 2.
Map of Singapore showing the locations of new species records. Numbers in parentheses indicate the new records in each location as shown in Table 2, first column.
Concerning filariasis, Culex quinquefasciatus is incriminated as the primary vector of Wuchereria bancrofti in Singapore (Danaraj et al. 1958, as Culex fatigans, Colbourne and Ng 1972). There were also several local cases reported in the 1980s and the Cx. quinquefasciatus adults caught from the surroundings of patients' houses were positive for filarial worms (Lim and Phua 1997). Since then, there have been no further reports of local filarial disease, except for a recent imported asymptomatic microfilaremia in a relapsing P. vivax case (Chavatte and Jureen 2017).
As for Japanese encephalitis virus, Culex tritaeniorhynchus and Culex gelidus are considered vectors in Singapore, and field-caught samples have been found to be positive for the virus (Yin-Coggrave and Pong 1964). Japanese encephalitis virus was endemic in Singapore in the earlier years, but the incidence of reported cases has become very low since the complete phasing out of pig farming in 1992. In general, Japanese encephalitis virus is transmitted principally by Cx. tritaeniorhynchus (Koh et al. 2006) and less frequently by Cx. gelidus Theobald. In other countries, Japanese encephalitis virus has been detected in Mansonia uniformis (Theobald), Culex bitaeniorhynchus Giles, Culex pseudovishnui Colless, and Culex vishnui Theobald (Vythilingam et al. 1995).
Among the 25 vector species identified, nine species are recognized as vectors and two species have potential epidemiological importance in Singapore (Table 3). The remaining 14 species are known as vectors or potential vectors in neighboring countries, but have thus far not been implicated in disease transmission in Singapore. Nevertheless, their presence may pose risks to local transmission and should be assessed, in the event that their associated pathogens are introduced into the country.
This revised checklist provides the most updated species records in Singapore and should form the basis for future works, including the development of identification tools, research on mosquito bionomics and distribution, and risk assessment of mosquito–borne disease transmission.
Notes
Aedes (Cancraedes) masculinus Mattingly, 1958.
This species was initially reported in Singapore as Aedes (Skusea) curtipes Edwards, by Edwards (1928) and Edwards and Given (1928). Knight and Hull (1953) transferred Ae. curtipes from subgenus Skusea to subgenus Cancaedes of genus Aedes. Mattingly (1958) determined the species called Ae. curtipes in Singapore represented a new species, which he named and described Ae. masculinus.
Aedes (Downsiomyia) leonis Colless, 1958.
This species was originally reported from Singapore as Aedes (Finlaya) niveus ssp. leonis by Colless. Considering the recommendation of Dr. Kenneth L. Knight, who worked on the subgenus Finlaya species, including Ae. niveus for many years, Harrison et al. (1990) agreed with the recommendation and elevated this subspecies to species status. Subsequently, Wilkerson et al. (2015) placed it in subgenus Downsiomyia following the recognition of this group of species by Reinert et al. (2004).
Aedes (Lorrainea) amesii (Ludlow, 1903).
Edwards (1926) mistakenly described that larvae he thought were this species from Singapore. In 1928, he determined the larva figured in 1926 was actually a new species, which he described as Aedes (Skusea) fumidus. He also renamed the other specimens he described in 1926 as Aedes (Skusea) furvus, which was done because the first available synonym, Stegomyia fusca Leicester 1908, for Ae. amesii, was already occupied. Subsequently, Ae. fusca (Leicester) and Ae. furvus Edwards were both synonymized (Stone et al. 1959) under Ae. amesii. Fortunately, Mattingly (1959) was able to obtain sufficient specimens to determine that both Ae. amesii and Ae. fumidus occurred in Singapore. Thus, the first record of Ae. amesii collected in Singapore was the specimens mistakenly named Ae. furvus by Edwards (1928), and not the Ae. (Lor.) amesii specimens reported as a new record by Jeffery et al. (2010).
Aedes (Phagomyia) near khazani Edwards, 1922.
During this study, a single female of this species from Singapore was located and examined in the Lee Kong Chian Natural History Museum (LKCNHM), Singapore. Although this female is clearly similar to Ae. khazani, there are slight differences from the original description based on Indian specimens and also specimens from Thailand (Rattanarithikul et al. 2010).
Aedes (Stegomyia) malayensis Colless, 1962.
This species was initially recorded in Singapore as Aedes (Stegomyia) hensilli Farner, by Colless (1957c). Colless (1962) recognized that he misidentified those specimens, and that they were part of the Aedes scutellaris group. Consequently, he named them Ae. (Stg.) scutellaris ssp. malayensis. Huang (1972) elevated this subspecies to species status.
Anopheles (Anopheles) barbirostris sensu lato.
Colless (1959a) recorded this species (as An. barbirostris) collected in net-traps in Singapore. Recently, at least four new cryptic species have been described in the An. barbirostris complex (Townson et al. 2013, Taai and Harbach 2015) and one new species remains undescribed (Saeung et al. 2008). This raises the number of species in the An. barbirostris subgroup (Harbach 2013) to seven species. Currently, morphological identification of females of the An. barbirostris Subgroup is unreliable. Thus, the identity of the specimens that Colless collected is unknown, as is the identity of specimens recently collected by Lee et al. (2012) on Ubin Island.
Anopheles (Anopheles) fragilis (Theobald, 1903).
This species is recorded in Singapore for the first time in Table 2. The fine aciculae on the middle portion of larval seta 2-C are difficult to see without >50× magnification, but are diagnostic for An. fragilis regardless of the variable 2-C single to trifid branched stem illustrated in Reid (1968, p. 235) and Rattanarithikul et al. (2006a, p. 98). We suspect that Colless (1957a) did not see the minute aciculae on larval seta 2-C of the specimens he identified as Ae. aitkenii James, whose distribution has been restricted to the Indian Subregion (Harrison and Scanlon 1975) of the Oriental Region.
Anopheles (Anopheles) paraliae Sandosham, 1959.
This species was originally described as a subspecies in Malaya of Anopheles (Ano.) lesteri Baisas and Hu described from the Philippines. Harrison et al. (1990) elevated An. (Ano.) lesteri ssp. paraliae to species status based on its distribution in Southeast Asia and basic biological differences of this species from An. lesteri. Anopheles paraliae is a lowland coastal species whose larvae are usually found in brackish water, whereas An. lesteri from the Philippines extends north onto mainland Asia to northern China, Korea, and Japan. Larvae of the latter species are found in freshwater in the Philippines and far inland in China. Recently, Taai et al. (2013) provided evidence suggesting that these two taxa are very closely related or possibly conspecific; however, they refrained from synonymizing An. paraliae under An. lesteri until further work was conducted. Behavioral and biological differences play important roles in the process of speciation. Comparing two species from two very widely separated sites (thousands of miles in this case) does not prove that they will be compatible where they occur near to each other. We contend that crossing experiments and/or rDNA ITS2 molecular analysis should be conducted between An. paraliae from Malaysia, Thailand, or Vietnam and An. lesteri from near the type locality in the Philippines instead of comparing a strain of An. paraliae from southern Thailand and An. lesteri from South Korea. Thus, we will list this species in Singapore until this taxonomic problem is resolved.
Anopheles (Anopheles) nitidus Harrison, Scanlon, and Reid, 1973.
Colless (1957a) recorded this species in Singapore as Anopheles (Ano.) indiensis Theobald. Harrison et al. (1973) determined that An. indiensis of Reid (1953, 1968) did not occur in Madras, India, the type locality of An. indiensis Theobald. Furthermore, the type of An. indiensis is lost and no other specimens have been found. Thus, Harrison et al. (1973) synonymized An. indiensis with Anopheles nigerrimus Giles, 1900, and renamed An. indiensis of Reid in Malaysia, Singapore, and Thailand as An. nitidus. Additional information about this species is provided in Harrison and Scanlon (1975).
Anopheles (Cellia) epiroticus Linton and Harbach, 2005.
Initially, this species was reported to be common in Singapore by James and Stanton (1912, as ludlowi (sic) Theobald). Rodenwaldt (1925) determined that the name ludlowi should be applied to a Philippine species and the correct name for the species in Malaya (which included Singapore at that time) was actually Anopheles sundaicus (Rodenwaldt 1925). Reid (1968) briefly discussed differences he recognized between An. sundaicus from Peninsular Malaya and those from the Malay States on the Island of Borneo. Linton et al. (2005) designated a neotype for An. sundaicus from Sarawak, Borneo, and described a new species, An. epiroticus Linton and Harbach, based on those mainland specimens previously called An. sundaicus in Cambodia, Peninsular Malaysia, Thailand, and Vietnam. They also retained the name An. sundaicus for the species in East Malaysia. The accuracy of this identification was confirmed by the ITS2 sequences of Singapore specimens in the collections of the Natural History Museum, London (Linton, personal communication). Accordingly, we accept An. epiroticus as the species in Singapore, which is only 1.6 km from Peninsular Malaysia.
Anopheles (Cellia) maculatus sensu lato.
The importance of An. maculatus as a vector of malaria in Malaya was documented by Reid (1968). Reid (1970) suggested that An. maculatus may be a complex of species that could not be identified by morphology. Chan (1969) documented An. maculatus in Singapore, but by that time it was in low numbers. Green et al. (1985) discovered that at least three cryptic species were masquerading under the name An. maculatus. In that study, it was determined that Form B occurred primarily in Thailand, whereas Form E occurred primarily in Malaysia. Rattanarithikul and Green (1986) formally recognized and described two new species in the An. maculatus group. Kittayapong et al. (1992) conducted a malaria study in Perak, Malaysia, and the primary vector was Form E, with a high percentage of the studied specimens infected with one to three human malaria parasites. By 2007, eight species were recognized in the An. maculatus group (Walton et al. 2007), but species status for Form E remains unresolved. Although we suspect An. maculatus Form E is what occurs in Singapore, this has not been proven.
Anopheles (Cellia) subpictus Grassi, 1899.
This species was recorded in Singapore as Anopheles rossii Giles, by Leicester (1908). Anopheles rossii was recognized as a junior synonym of An. subpictus by Edwards (1932).
Armigeres (Armigeres) subalbatus (Coquillett, 1898).
Colless (1957a) reported Armigeres obturbans (Walker) as one of the two common species in Singapore. Macdonald (1958) listed “Ar. obturbans (= subalbatus)” ranging from India through the Malay Archipelago to New Guinea and northern Australia. Ramalingam (1987) and Jeffery et al. (2010) clarified the Ar. obturbans versus Ar. subalbatus records, pointing out that although Lee et al. (1988a) determined that Ar. obturbans is a valid species, it is restricted to the island of Sulawesi (= Celebes) and Ar. subalbatus is the correct name for the common Southeast Asian species previously called Ar. obturbans. Recently Lee et al. (2012) collected nine females of Ar. subalbatus on Ubin Island, Singapore.
Coquillettidia (Coquillettidia) crassipes (van der Wulp, 1881).
Edwards and Given (1928) illustrated the antenna of a larva collected in Singapore that they cautiously called Taeniorhynchus (Coquillettidia) sp., which they said was probably Taeniorhynchus brevicellulus Theobald or Taeniorhynchus ochraceus Theobald ‘both of which were found to be common in Singapore’. Brug and Bonne-Wepster (1947) reported Mansonia crassipes in Singapore. Wharton (1962) determined that the unidentified larval description and illustration from Singapore (Edwards and Given 1928) was Ma. (Coq.) crassipes. T. brevicellulus is now recognized as a junior synonym of Cq. crassipes (Stone et al. 1959, Knight and Stone 1977). Lee et al. (2012) collected two females of Cq. crassipes on Ubin Island, Singapore.
Culex (Culex) alis Theobald, 1903.
Colless (1957b) first recorded this species in Singapore as Culex (Culex) litoralis Bohart. Sirivanakarn (1976) examined the specimens Colless identified from Pulau Hantu, Singapore and determined that they are Culex alis.
Culex (Culex) quinquefasciatus Say, 1823.
For years, Culex (Culex) fatigans Wiedemann was the name used for this species, particularly in the Orient, and Colless (1957b) considered this species common in Singapore. However, Sirivanakarn (1976) determined that Cx. fatigans is a junior synonym of Cx. quinquefasciatus. Danaraj et al. (1958) presented an overview of the importance of this vector species in the transmission of filariasis in Singapore. Lee et al. (2012) collected this species on Ubin Island, Singapore.
Culex (Culex) vishnui Theobald 1901.
Colless (1957a,b) recorded this species, as Culex (Culex) annulus Theobald as common in Singapore. Reuben (1969), after having the type specimens for these two species reexamined at the British Museum, determined that Cx. annulus is a junior synonym of Cx. vishnui, and Sirivanakarn (1976) agreed with this finding, but considered most of the females in the Vishnui Subgroup to be inseparable.
Culex (Eumelanomyia) brevipalpis (Giles, 1902).
Theobald (1901) first described this species as Culex longipes, with the type specimen from Singapore, but this name was preoccupied by Cx. longipes Fabricius, and not available for use. Thus, the next available name was Stegomyia brevipalpis Giles, which was corrected to Cx. brevipalpis by Theobald (1903). In the world catalogs of mosquitoes (Stone et al. 1959, Knight and Stone 1977), Cx. longipes is recognized as a junior synonym of Cx. brevipalpis and Theobald's type for Cx. longipes is located in the Natural History Museum, London (Sirivanakarn 1972). Five larvae of this species were recently collected on Ubin Island, Singapore by Lee et al. (2012).
Culex (Lophoceraomyia) minor (Leicester 1908).
Edwards (1928) and Edwards and Given (1928) recorded Cx. minor from rock pools in Singapore. More recently there has been a problem separating Cx. minor from Culex bicornutus. Colless (1965) examined 114 males and found Cx. minor specimens from Singapore, and said that Cx. bicornutus ‘probably’ occurred there. However, Sirivanakarn (1977) apparently overlooked the record of Cx. minor in Singapore by Colless (1965). Because of the larval habitat differences for these two species discussed in Colless (1965), we have decided to follow Colless and record Cx. minor from Singapore.
Culex (Lophoceraomyia) reidi Colless 1965.
Edwards and Given (1928) recorded this species in Singapore as Culex quadripalpis Edwards. Colless (1965) determined that the larval specimens identified as Cx. quadripalpis by Edwards and Given were actually a new species, which he described as Cx. reidi based on Singapore specimens.
Heizmannia (Heizmannia) scintillans Ludlow, 1905.
This species was first recorded in Singapore as a larva of Heizmannia funerea (Leicester) by Edwards and Given (1928). Mattingly (1957b) examined the larva and determined it was Hz. scintillans, not Hz. funerea. Also, Mattingly (1970) examined additional specimens of Hz. scintillans from Singapore.
Mimomyia (Etorleptiomyia) luzonensis (Ludlow, 1905).
Leicester (1908) established the first record of this species in Singapore when he described Etorleptiomyia completiva, which is now considered to be a junior synonym of Mimomyia luzonensis. Edwards and Given (1928) described a larva of this species, as Mimomyia species, but being uncertain they suspected it was Ficalbia minima (Theobald). Mattingly (1957a) provided an enhanced description for Mi. luzonensis.
Orthopodomyia albipes Leicester, 1904 (in Theobald, 1904).
The three species, Orthopodomyia albipes, Orthopodomyia andamanensis and Orthopodomyia anopheloides, are extremely difficult to distinguish without reared specimens that also have associated larval and pupal exuviae. Zavortink (1968) resolved some, but not all, of the identification problems and documented Or. andamanensis and Or. anopheloides in Singapore, but not Or. albipes. Finally, Zavortink (1971) found one larva that he identified as Or. albipes from Singapore.
Orthopodomyia anopheloides Giles, 1903 (in Thomson, 1903).
Zavortink (1968) determined that the Edwards (1926) record of Orthopodomyia maculipes Theobald in Singapore was a specimen of Orthopodomyia anopheloides.
Toxorhynchites (Toxorhynchites) splendens (Wiedemann, 1819).
Brunetti (1920) recorded this species in Singapore. However, Lee et al. (1988b) considered the record of Toxorhynchites speciosus (Skuse) in Singapore by Colless (1957a) a ‘probable’ misidentification of Tx. splendens.
Tripteroides (Rachionotomyia) tenax (de Meijere, 1910). Edwards (1926) and Edwards and Given (1928) reported Rachionotomyia aranoides (Theobald) as very common in pitcher plants in Singapore. However, Mattingly (1981) determined that Tripteroides aranoides larvae were found in bamboo habitats, whereas Tp. tenax, a junior synonym of Tp. aranoides, was the species in pitcher plants in Singapore. Accordingly, he elevated Tp. tenax to species status. Based on these actions, Tp. aranoides has been replaced by Tp. tenax and is no longer recognized in Singapore.
Uranotaenia (Pseudoficalbia) moultoni Edwards, 1914.
Based on larvae collected by Dr. Given, Edwards (1926) and Edwards and Given (1928) recorded this species in Singapore as Uranotaenia brevirostris Edwards. Barr and Chellapah (1963) also recorded Ur. brevirostris in Singapore, in pitcher plants. However, Peyton (1972) synonymized Ur. brevirostris with Ur. moultoni.
Verrallina (Verrallina) butleri (Theobald 1901).
Edwards and Given (1928) collected larvae of this species in potholes and crab holes in an uncut mangrove area and identified them as Aedes (Aedes) umbrosus Brug. Knight and Hull (1953) synonymized Ae. umbrosus with Ve. butleri. Reinert (1974) recorded specimens of Ve. butleri from Singapore, and more recently Lee et al. (2012) collected this species on Ubin Island, Singapore.
Table 3.
Mosquito species in Singapore and neighboring countries which are incriminated as vectors or with potential epidemiological importance in transmitting human diseases
Excluded Species
Aedes (Cancraedes) curtipes Edwards, 1915.
Apiwathnasorn (1986) recorded this species in Singapore. However, it was originally described based on a single female from Sarawak, Malaysia (as Borneo). Later, Edwards (1928) described a male from Singapore as Ae. curtipes and Edwards and Given (1928) identified larvae and pupae from Singapore as this species. Mattingly (1958) discovered the male identified as Ae. curtipes by Edwards was not the same species as the female holotype of Ae. curtipes from Sarawak, and the male Edwards identified, and the larvae and pupae identified by Edwards and Given, represented a new species which he described as Aedes (Cancraedes) masculinus (Note 1). Mattingly (1958) listed the distribution of Ae. curtipes as Sarawak (as Borneo), Sulawesi (as Celebes) and Luzon, Samar, and Mindanao in the Philippines. He also said this species ‘is quite distinct and does not occur in Malaya or Singapore.’ Therefore, we have deleted Ae. curtipes from the list of Singapore species.
Aedes (Fredwardsius) vittatus (Bigot, 1861).
Apiwathnasorn (1986) recorded this species in Singapore. It is widely distributed from France, throughout Africa, Aden, Yemen, India, across Southeast Asia to Vietnam, and in China. But according to Huang (1977) and Reinert (2000), it does not occur further south of northern Peninsular Malaysia (Penang and Langkawi Island) in Southeast Asia. Thus, we have deleted Ae. vittatus from the list of Singapore species.
Aedes (Stegomyia) aegypti var. queenslandensis (Theobald, 1901).
Aedes aegypti (L.) and Aedes aegypti var. queenslandensis were recorded in Singapore by Apiwathnasorn (1986). However, Lee et al. (1987) synonymized the varietal name queenslandensis under Ae. aegypti, and this change was entered into the world catalog of mosquitoes (Knight and Stone 1977, Ward 1992, p. 190). Accordingly, the name queenslandensis has no official status other than being a junior synonym of Ae. aegypti. Jeffery et al. (2010) adequately explained this, but it was overlooked by Chan et al. (2014) who again used queenslandensis as an official varietal name. We disagree with this use of the name because the name was not available for use without formal justification; thus, it is not included in the list of Singapore mosquito taxa.
Aedes (Stegomyia) hensilli Farner, 1945.
Apiwathnasorn (1986) did not record this species in Singapore, but Colless (1957c) reported it based on specimens from Pulau Hantu, Singapore. However, during revisionary work on the Scutellaris Group of Southeast Asia, Huang (1971) redescribed Aedes scutellaris malayensis and in 1972 discovered that Colless had misidentified Ae. scutellaris malayensis in Singapore as Ae. hensilli (Note 5). This discovery means Ae. hensilli is not found anywhere near Singapore, because Knight and Stone (1977) listed the distribution of Ae. hensilli as limited to the Caroline and Palau Islands in the South Pacific Region.
Anopheles (Anopheles) aitkenii James, 1903.
Apiwathnasorn (1986) did not list An. aitkenii in Singapore, but Colless (1957a) did. Although Harrison and Scanlon (1975) restricted the distribution of this species to the Indian Region of Asia, there are three other species of the Aitkenii Group in Peninsular Malaysia that might be misidentified as An. aitkenii, and also may possibly occur in Singapore: Anopheles aberrans Harrison and Scanlon, 1975; Anopheles bengalensis Puri, 1930; and Anopheles fragilis (Tables 1 and 2). Currently, we can vouch for only one member of the Aitkenii Group in Singapore, i.e., An. fragilis, which is a new record for Singapore (Tables 1 and 2). Although discussed earlier (Note 7), we suspect that An. fragilis was the species Colless misidentified, but this cannot be proven. Both An. aberrans and An. bengalensis lack the minute aciculae on larval seta 2-C, and both have variable branching of 2-C, i.e., An. aberrans (2–13 branches) and An. bengalensis (single to nine branches) (Harrison and Scanlon 1975). Thus, larval specimens of these two species with head seta 2-C bifid could be confused with An. aitkenii.
Anopheles (Cellia) minimus, Theobald, 1901.
Reid (1968) and Harrison (1980) agreed that on mainland Southeast Asia, this species does not extend further south than the northern state of Perlis in Peninsular Malaysia. Thus, Apiwathnasorn (1986) erred in recording An. minimus from the nonmainland countries of Indonesia, Singapore, Philippines, and the Island of Borneo (including Brunei, Kalimantan, Sabah, and Sarawak). Harrison (1980, pp. 19–20) determined that the species likely to occur in these last named areas is Anopheles flavirostris Ludlow, 1914; however, An. flavirostris has not been reported in Singapore. Also, we have not found a publication, other than Apiwathnasorn (1986) reporting An. minimus in Singapore. For these reasons, An. minimus is not included in the Singapore list of species.
Armigeres (Armigeres) obturbans (Walker, 1859).
Apiwathnasorn (1986) did not record this species in Singapore. Ar. obturbans was described from Sulawesi, and currently its distribution is restricted to Sulawesi. However, for many years, this species was considered the common peridomestic Armigeres species in the Australiasian and Oriental Regions, and was recorded in Singapore by Colless (1957a). Thurman (1959), Stone et al. (1959), and Knight and Stone (1977) considered this name a ‘doubtful name’ (= nomen nudum) because the type specimen was considered lost and a precise identification of the species was impossible. Ramalingam (1987) also considered this species a nomen nudum, and added that Armigeres subalbatus (Note 13) was the common peridomestic Oriental species extending from Japan, Pakistan, India, Sri Lanka, and through the Southeast Asian countries. Lee et al. (1988a) reported the female holotype of Ar. obturbans had been found and they provided a character found on the holotype that is distinct from other known Armigeres, but they left it as a nomen nudum. We consider Ar. obturbans a valid species based on the distinguishing character described by Lee et al. (1988a). Regardless, Ar. obturbans is not included in the Singapore list of species and is restricted in distribution to Sulawesi, as suggested by Thurman (1959) and confirmed by Lee et al. (1988a).
Culex (Culex) litoralis Bohart and Ingram, 1946.
This species was recorded in Singapore by Colless (1957b) and added to the distribution of this species in the world catalog of mosquitoes (Knight and Stone 1977). After Colless established this record, it was determined that it was a misidentification of Cx. alis (Note 15). Determining that Cx. litoralis did not occur in Singapore solidified the Central and Western Pacific distribution of Cx. litoralis, i.e., Mariana Islands, New Guinea, Samoa Islands, and Society Islands. Thus, Apiwathnasorn (1986) erred in recording this species in Singapore.
Culex (Culex) mimeticus Noe, 1899.
Although Apiwathnasorn (1986) recorded this species in Singapore, we have been unable to find published information documenting this report. According to Sirivanakarn (1976), Cx. mimeticus is widely distributed from southern Europe and northern Africa across the Middle East and northern India, Tibet (up to 3,050 m), China, Taiwan, Japan, Korea, and to high elevations sites in Myanmar, Peninsular Malaysia, and Vietnam. The southern-most collection appears to be in Cameron Highlands, Pahang State, Peninsular Malaysia, in a rock pool at 1,450 m (Macdonald 1957). Sirivanakarn said ‘it appears to be restricted to high elevations in India, Burma (Barraud 1934), Southeast Asia and other adjacent areas’.
According to Jeffery et al. (2010), the highest elevation in Singapore is 166 m. However, specimens of Cx. mimeticus from Singapore were located in the National Museum of Natural History, Smithsonian Institution, Washington, D.C. and their identification is questionable. Until their identification is confirmed using the recent key of Rattanarithikul (2005), Cx. mimeticus is not listed as a Singapore species.
Culex (Culex) whitmorei (Giles, 1904).
Apiwathnasorn (1986) recorded this species in Singapore, but we have been unable to verify this record. It was reported from Peninsular Malaya (Macdonald 1957), and this was included in the world catalog (Knight and Stone 1977). But, in Bram (1967) and the very thorough revision of Culex (Culex) in Southeast Asia (Sirivanakarn 1976), Singapore is not included in the distribution of this species. Thus, we consider the record of Cx. whitmorei in Singapore an error.
Acknowledgments
We thank the staff of the Singapore Armed Forces and National Environment Agency for contributing specimens to the EHI mosquito collection through routine mosquito surveillance. We are grateful to J. Rajarethinam and S. -H. Liang for their help in generating the map. In addition, we thank R. Harbach and I. Vythilingam for their assistance in searching for specimens collected from Singapore in the Natural History Museum (NHM), London, and Museum of Zoology, University of Malaya (MZUM), respectively. Two anonymous reviewers provided useful comments that improved this manuscript. The opinions contained herein are those of the authors and EHI and do not reflect official views of the supporting agency Walter Reed Army Institute of Research (WRAIR).
