Accurate identification of mosquitoes is crucial for the management and control of vector species. Although Singapore is a tropical country with high mosquito diversity, there are no identification keys specific to its mosquito fauna. An illustrated identification key to the genera of the adult female mosquitoes of Singapore is presented. Twenty genera are characterized and two genera found in Malaysia, Culiseta and Topomyia, are also included. The key will aid non-taxonomically trained operational officers in adult mosquito identification. The key to the genera provides the first crucial step in the process to species identification.
There has been a worldwide surge in the number and severity of dengue in the past decades. In Singapore, relentless vector control efforts have been put in to control the disease since the 1960's. Space spraying, fogging, chemical treatment and source reduction are some commonly used methodologies for controlling its vectors, particularly Aedes aegypti. Here, as we explored the use of a commercially available delthamethrin-treated net as an alternative strategy and the efficacy of the treated net was found to be limited. Through bioassays and molecular studies, the failure of the treated net to render high mortality rate was found to be associated with the knockdown resistance (kdr) mutation. This is the first report of kdr- mutations in Singapore's Ae. aegypti. At least one point mutation, either homozygous or heterozygous, at amino acid residue V1016G of DIIS6 or F1269C of DIIIS6 was detected in 93% of field strains of Ae. aegypti. Various permutations of wild type and mutant amino acids of the four alleles were found to result in varying degree of survival rate among local field Ae. aegypti when exposed to the deltamethrin treated net. Together with the association of higher survival rate with the presence of both V1016G and F1269C, the data suggest the role of these mutations in the resistance to the deltamethrin. The high prevalence of these mutations were confirmed in a country wide survey where 70% and 72% of the 201 Ae. aegypti analysed possessed the mutations at residues 1016 and 1269 respectively. The highest mutated frequency combination was found to be heterozygous alleles (VG/FC) at both residues 1016 and 1269 (37.8%), followed by homozygous mutation at allele 1269 (24.4%) and homozygous mutation at allele 1016 (22.9%). The kdr- type of resistance among the vector is likely to undermine the effectiveness of pyrethroids treated materials against these mosquitoes.
Nine species of mosquitoes in eight genera are recorded for the first time in Singapore. An additional two species were overlooked in a 1986 checklist for mosquitoes in Singapore, and one was described after 1986. Location and habitat data are provided for the nine new records. With the inclusion of these new records the number of species reported from Singapore is 137.
Mosquito-borne flaviviruses are emerging pathogens of an increasing global public health concern because of their rapid increase in geographical range and the impact of climate change. Japanese encephalitis virus (JEV) and West Nile virus (WNV) are of concern because of the risk of reemergence and introduction by migratory birds. In Singapore, human WNV infection has never been reported and human JEV infection is rare. Four sentinel vector surveillance sites were established in Singapore to understand the potential risk posed by these viruses. Surveillance was carried out from August 2011 to December 2012 at Pulau Ubin, from March 2011 to March 2013 at an Avian Sanctuary (AS), from December 2010 from October 2012 at Murai Farmway, and from December 2010 to December 2013 at a nature reserve. The present study revealed active JEV transmission in Singapore through the detection of JEV genotype II in Culex tritaeniorhynchus collected from an Avian Sanctuary. Culex flavivirus (CxFV), similar to the Quang Binh virus isolated from Cx. tritaeniorhynchus in Vietnam and CxFV-LSFlaviV-A20-09 virus isolated in China, was also detected in Culex spp. (vishnui subgroup). No WNV was detected. This study demonstrates the important role that surveillance plays in public health and strongly suggests the circulation of JEV among wildlife in Singapore, despite the absence of reported human cases. A One Health approach involving surveillance, the collaboration between public health and wildlife managers, and control of mosquito populations remains the key measures in risk mitigation of JEV transmission in the enzootic cycle between birds and mosquitoes.
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.