Displaying publications 1 - 20 of 122 in total

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  1. Adler PH, Takaoka H, Sofian-Azirun M, Chen CD, Suana IW
    Acta Trop, 2019 May;193:1-6.
    PMID: 30772330 DOI: 10.1016/j.actatropica.2019.02.017
    A recently described species of black fly, Simulium wayani Takaoka and Chen, from the island of Timor was chromosomally mapped to provide insights into its evolutionary and biogeographic history. The morphologically based species status of S. wayani is supported by a suite of fixed chromosomal rearrangements and unique sex chromosomes derived primarily from a large pool of polymorphisms in the S. ornatipes complex in Australia. The banding patterns of its polytene chromosomes indicate that S. wayani is closely related to a pair of homosequential cryptic species (S. norfolkense Dumbleton and S. ornatipes cytoform A2) in the S. ornatipes Skuse complex on mainland Australia; all three species uniquely share the same amplified band in their chromosomal complement. The low level of polymorphism and heterozygosity in S. wayani, relative to Australian populations of the S. ornatipes complex, suggests few colonization events from the larger land mass.
  2. Adler PH, Takaoka H, Sofian-Azirun M, Low VL, Ya'cob Z, Chen CD, et al.
    PLoS One, 2016;11(10):e0163881.
    PMID: 27695048 DOI: 10.1371/journal.pone.0163881
    The increasing attention on Vietnam as a biodiversity hotspot prompted an investigation of the potential for cryptic diversity in black flies, a group well known elsewhere for its high frequency of isomorphic species. We analyzed the banding structure of the larval polytene chromosomes in the Simulium tuberosum species group to probe for diversity beyond the morphological level. Among 272 larvae, 88 different chromosomal rearrangements, primarily paracentric inversions, were discovered in addition to 25 already known in the basic sequences of the group in Asia. Chromosomal diversity in Vietnam far exceeds that known for the group in Thailand, with only about 5% of the rearrangements shared between the two countries. Fifteen cytoforms and nine morphoforms were revealed among six nominal species in Vietnam. Chromosomal evidence, combined with available molecular and morphological evidence, conservatively suggests that at least five of the cytoforms are valid species, two of which require formal names. The total chromosomal rearrangements and species (15) now known from the group in Vietnam far exceed those of any other area of comparable size in the world, supporting the country's status as a biodiversity hotspot. Phylogenetic inference based on uniquely shared, derived chromosomal rearrangements supports the clustering of cytoforms into two primary lineages, the Simulium tani complex and the Southeast Asian Simulium tuberosum subgroup. Some of these taxa could be threatened by habitat destruction, given their restricted geographical distributions and the expanding human population of Vietnam.
  3. Amelia-Yap ZH, Chen CD, Sofian-Azirun M, Low VL
    Parasit Vectors, 2018 Jun 04;11(1):332.
    PMID: 29866193 DOI: 10.1186/s13071-018-2899-0
    Human arboviral diseases transmitted by Aedes aegypti such as dengue, Zika, chikungunya and yellow fever remain global public health threats to date. Of these diseases, dengue fever is particularly prevalent in Southeast Asia. Relentless vector control efforts are performed to curtail disease transmissions through which pyrethroid insecticides are broadly used as the first line of defense to control Ae. aegypti, especially in the course of disease outbreaks. Here, we compile the largest contemporary database for susceptibility profiles and underlying mechanisms involved in Ae. aegypti resistant to pyrethroids in Southeast Asia. The extensive use of pyrethroids inevitably elicit different levels of resistance to numerous populations despite the presence of geographical isolation. The most common mechanisms of pyrethroid resistance that have been identified in Ae. aegypti includes mutations in the voltage sensitive sodium channel gene (Vssc gene) and metabolic-mediated insecticide resistance. Aedes aegypti develops resistance to pyrethroids by acquisition of one or several amino acid substitution(s) in this Vssc gene. Enzymes involved in metabolic-mediated detoxification (i.e. monooxygenases, glutathione-S-transferases and esterases) have been reported to be related to pyrethroid resistance but many specific contributory enzymes are not completely studied. An inadequate amount of data from some countries indicates an urgent need for further study to fill the knowledge gaps. Perspectives and future research needs are also discussed.
  4. Amelia-Yap ZH, Sofian-Azirun M, Chen CD, Lau KW, Suana IW, Syahputra E, et al.
    J Med Entomol, 2019 06 27;56(4):953-958.
    PMID: 30942885 DOI: 10.1093/jme/tjz035
    Resistance to pyrethroid insecticides is widespread in Indonesian Aedes aegypti (Linnaeus), the primary vector of dengue viruses. This study aims to investigate the mutations in the voltage-gated sodium channel (Vgsc) conferring pyrethroid resistance against Ae. aegypti populations from Indonesia. Molecular genotyping of mutations using polymerase chain reaction assay and direct DNA sequencing were performed at positions 989 and 1,016 in IIS6 region, and 1,534 in IIIS6 region of the voltage-gated sodium channel (Vgsc) in nine populations of Indonesian Ae. aegypti. The V1016G and S989P genotyping identified the RR genotype to be predominant in six out of nine populations of Ae. aegypti, whereas the SS genotype occurred only in minority. Interestingly, co-occurrence of the V1016G and S989P mutations was detected in the aforementioned six populations with high frequency. Genotyping of F1534C showed all nine populations exhibited the SS genotype, with merely two individuals from a population were heterozygous (RS). Significant correlations were demonstrated between the allele frequencies of the V1016G mutation and the survivability rates as well as resistance ratios in pyrethroid adult bioassays. This signifies the V1016G can contribute more to the insensitivity of Vgsc than the F1534C. Homozygous 1016G mosquitoes were likelier to survive pyrethroid exposure. Identification of underlying mechanisms resulting in insecticide resistance is advantageous in developing effective mosquito control programs in Indonesia.
  5. Amelia-Yap ZH, Sofian-Azirun M, Chen CD, Suana IW, Lau KW, Elia-Amira NMR, et al.
    J Med Entomol, 2019 04 16;56(3):811-816.
    PMID: 30715464 DOI: 10.1093/jme/tjz007
    The emergence of pyrethroid resistance in Aedes aegypti (L.) has limited the success of vector control. Early detection of resistance could assist authorities in deciding well-suited control strategies to minimize operational failures of Ae. aegypti control. Herein, biochemical analysis was performed to investigate the mechanisms involved in pyrethroid resistance in nine populations of Indonesian Ae. aegypti. Enzymes of adult Ae. aegypti such as esterases (ESTs), glutathione-S-transferases (GSTs), and mixed-function oxidases (MFOs) were characterized. Elevated MFO activity was correlated with resistance phenotype, indicating the role of this enzyme in contributing to pyrethroid resistance. No significant correlations were shown between pyrethroid resistance phenotype and α-ESTs, suggesting that marginally exceeded enzyme levels relative to the reference strain in some pyrethroid-susceptible populations were causative factor for insecticide resistance in other groups of insecticides. However, significant correlation was demonstrated between β-ESTs and pyrethroid resistance phenotype. The lowest enzyme levels in GSTs indicated that this enzyme was not predominant in causing pyrethroid resistance, despite the presence of significant correlations. Because metabolic detoxification fails to comprehensively explain the pyrethroid resistance in some Indonesian Ae. aegypti, additional mechanisms such as altered target sites in voltage-gated sodium channel may also contribute to the high pyrethroid resistance in Ae. aegypti.
  6. Amelia-Yap ZH, Chen CD, Sofian-Azirun M, Lau KW, Suana IW, Harmonis, et al.
    J Econ Entomol, 2018 12 14;111(6):2854-2860.
    PMID: 30265353 DOI: 10.1093/jee/toy296
    Aedes aegypti (L.) (Diptera: Culicidae) is the primary vector of several arthropod-borne viral infectious diseases globally. Relentless vector control efforts are performed to curtail disease transmissions, insecticides remain as the first line of defense in Indonesia. With a dearth of publication on the efficacy of mosquito coil in Indonesia, this is the first report related to mosquito coil despite its common use in households. Ae. aegypti mosquitoes were sampled from nine regencies in Indonesia and tested using the glass-chamber method against three commercially available local pyrethroid-based mosquito coils containing d-allethrin, transfluthrin, and metofluthrin. The 50% knockdown time of female Ae. aegypti tested with d-allethrin, transfluthrin, and metofluthrin containing coils ranged from 0.65 to 14.32; 0.8 to 16.4; and 0.78 to 20.57 min, respectively. Mortality rates in accordance with WHO resistance indicators showed that strains from Denpasar, Mataram, Kuningan, Padang, Samarinda, and Sumba Timur were resistant (<80% mortality rate), whereas strains from Manggarai Barat, Dompu, and Pontianak were susceptible (>98% mortality rate) to the active ingredients assayed. Moreover, the knockdown rates between d-allethrin and transfluthrin, d-allethrin and metofluthrin, as well as transfluthrin and metofluthrin displayed significant associations, portraying the presence of cross-resistance within pyrethroid insecticides. The minimal insecticidal effect of mosquito coils against some Indonesian Ae. aegypti also pointed out the development of pyrethroid resistance, prompting a revamping of the vector control system.
  7. Amelia-Yap ZH, Tan TK, Prakash BK, Chen CD, Sofian-Azirun M, Low VL
    J Vector Borne Dis, 2020 10 1;57(4):359-361.
    PMID: 34856717 DOI: 10.4103/0972-9062.313959
  8. Azidah AA, Sofian-Azirun M
    Bull. Entomol. Res., 2006 Dec;96(6):613-8.
    PMID: 17201979
    The incubation period of Spodoptera exigua (Hübner) was not influenced by the host plant, whereas larval development time and pupal period were affected. Larval development time was longest on shallot and lady's finger, followed by cabbage and long bean. Larvae did not develop beyond the first instar when fed on chilli. The pupal period was longer on lady's finger than on cabbage, shallot and long bean. Overall, adult longevity was not influenced by the host plant but there was a difference between female and male longevity among the host plants. Survival of S. exigua was affected by the host plant at the larval stage. The number of larval instars varied between 5 and 8 within and between the studied host plants. Long bean was found to be the most suitable host plant and provide the best food quality for S. exigua compared to the other host plants, as it allowed faster development, fewer larval instars and a higher survival rate.
  9. Azratul-Hizayu T, Chen CD, Lau KW, Azrizal-Wahid N, Tan TK, Lim YAL, et al.
    Trop Biomed, 2021 Sep 01;38(3):327-337.
    PMID: 34508340 DOI: 10.47665/tb.38.3.073
    This study aims to examine the efficacy of mosquito mat vaporizers on Aedes aegypti and their associated metabolic detoxication mechanisms. For this purpose, Aedes aegypti (Linnaeus) was collected from nine districts in Selangor, Malaysia and tested with mosquito vaporizing mat bioassays. The same populations were also subjected to biochemical assays to investigate activities of detoxifying enzymes, namely non-specific esterase (EST), glutathione-S-transferase (GST) and mixed function oxidase (MFO). The efficacy of Ae. aegypti on the active ingredients tested in decreasing order were d- allethrin > dimefluthrin > prallethrin with PBO > prallethrin. The results further indicated significant enhancement mean levels of EST, GST and MFO in pyrethroid-resistant populations. The mortality rate of Ae. aegypti in response to pyrethroid active ingredients was associated with MFO activity, suggesting it is an important detoxification enzyme for the populations tested. In view of the presence of resistance against household insecticide products, pyrethroid efficacy on Ae. aegypti populations needs to be monitored closely to ensure the implementation of an effective vector control program in Malaysia.
  10. Azratul-Hizayu T, Chen CD, Lau KW, Azrizal-Wahid N, Tan TK, Lim YAL, et al.
    Parasitol Int, 2022 Feb;86:102483.
    PMID: 34678492 DOI: 10.1016/j.parint.2021.102483
    This study examines the biological efficacy of four mosquito mat vaporizers each containing different active ingredients: prallethrin with PBO, dimefluthrin, prallethrin, and d-allethrin. The glass chamber assay was used to evaluate their efficacy on Aedes albopictus (Skuse) (Diptera: Culicidae) from nine districts in Selangor, Malaysia. Aedes albopictus exhibited different knockdown rates, with 50% knockdown times, KT50, varying from 1.19 to 2.00 min, 1.22 to 2.20 min, 1.39 to 5.85 min, and 1.39 to 1.92 min for prallethrin with PBO, dimefluthrin, prallethrin and d-allethrin, respectively. In general, all populations of Ae. albopictus were completely knocked down after exposure to all active ingredients except Hulu Selangor population, which showed 96.00% knockdown against d-allethrin. On the contrary, mortality rates were observed from 84.00-100.00%, 84.00-100.00%, 90.67-100.00% and 90.67-100.00% in populations tested with prallethrin with PBO, dimefluthrin, prallethrin and d-allethrin, respectively. Moreover, significant correlations between mortality rates of prallethrin with PBO vs dimefluthrin (r = 0.836, P = 0.003), prallethrin with PBO vs prallethrin (r = 0.760, P = 0.011), and prallethrin vs d-allethrin (r = 0.694, P = 0.026) were also observed, suggesting cross-resistance among pyrethroids. d-allethrin was found to be high in insecticidal activity, followed by prallethrin, prallethrin with PBO, and dimefluthrin. In consistent with mortality due to insecticide exposure, elevated levels of enzyme activities were also demonstrated in Sabak Bernam, Hulu Selangor, Gombak, Petaling, Hulu Langat and Klang populations.
  11. Azrizal-Wahid N, Sofian-Azirun M, Low VL
    PMID: 33609991 DOI: 10.1016/j.cimid.2021.101621
    Flea-borne pathogens were screened from 100 individual cat fleas using a PCR approach, of which 38 % were infected with at least one bacterium. Overall, 28 % of the flea samples were positive for Bartonella as inferred from ITS DNA region. Of these, 25 % (7/28) were identified as Bartonella clarridgeiae, 42.9 % (12/28) as Bartonella henselae consisted of two different strains, and 32.1 % (9/28) as Bartonella koehlerae, which was detected for the first time in Malaysia. Sequencing of gltA amplicons detected Rickettsia DNA in 14 % of cat flea samples, all of them identified as Rickettsia asembonensis (100 %). None of the flea samples were positive for Mycoplasma DNA in 16S rRNA gene detection. Four fleas were co-infected with Bartonella and Rickettsia DNAs. Statistical analyses reveal no significant association between bacterial infection and mtDNA diversity of the cat flea. Nevertheless, in all types of pathogen infections, infected populations demonstrated lower nucleotide and haplotype diversities compared to uninfected populations. Moreover, lower haplotype numbers were observed in infected populations.
  12. Azrizal-Wahid N, Sofian-Azirun M, Low VL, Chen CD, Shohaimi S
    J Appl Anim Welf Sci, 2021 Sep 07.
    PMID: 34493142 DOI: 10.1080/10888705.2021.1975539
    A structured questionnaire was distributed to a total of 531 cat owners in Peninsular Malaysia to evaluate their perceptions toward fleas and flea-borne diseases (FBD) using a knowledge-attitude-practice (KAP) approach. This study showed that majority of cat owners (50.5%) had a moderate level of knowledge on fleas, while 65.3% of them had a relatively low level of knowledge on FBD. However, most of them had positive attitudes (87.9%) and good practices (94.5%) toward efforts on prevention from flea infestation and FBD. Statistical analysis showed significant associations between knowledge on fleas and FBD toward demographic and pet ownership profiles of the respondents. Educated cat owners from urban area were more likely to have positive attitudes toward prevention of fleas and FBD. Female cat owners with monthly income of RM 5,001-7,000 ($1143-1600) were more likely to have good practices. Middle-aged cat owners showed the highest odds toward both positive attitudes and good practices. Correlation analyses indicated significant linear relationships between both knowledge, which were also associated with attitudes, but not with practices.
  13. Azrizal-Wahid N, Sofian-Azirun M, Low VL
    Trop Biomed, 2019 Dec 01;36(4):810-821.
    PMID: 33597453
    Fleas are the common cause of skin disorders in cats. They are well-known for transmitting various pathogens to both cats and humans. Accordingly, this study was conducted to gain insights on the risk factors associated with flea infestation on cats. Flea combing conducted on 426 cats from four distinct regions in Peninsular Malaysia revealed a relatively high rate of flea infestation on 306 cats (71.83%). A total of 651 fleas were collected, all of them were identified as Ctenocephalides felis with the total intensity of 2.13 and abundance of 1.53. The sex ratio of fleas was female-biased at 2.5:1 (♀=464, ♂=187). Statistical analysis of the data revealed that flea infestation was significantly (P<0.05) associated with several risk factors including region, age, weight, status (stray, sheltered, pet), body condition, and hair length. Higher flea prevalence was also observed in female cats (77.99%), big-sized cats (91.76%), stray cats (84.94%), cats with clean body condition (73.35%), and cats with long hairs (78.38%) as compared to their contemporaries within the same comparison variables. The high infestation of fleas in this study is indicative of cats as a flea reservoir particularly C. felis. Thus the findings of this study and the knowledge gained on the risk factors can be used to develop and improve control measures and management of flea infestations.
  14. Azrizal-Wahid N, Sofian-Azirun M, Low VL
    Vet Parasitol, 2020 May;281:109102.
    PMID: 32289653 DOI: 10.1016/j.vetpar.2020.109102
    The present study investigated the genetic profile of the cosmopolitan cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae) from Malaysia and the reference data available in the National Center for Biotechnology Information (NCBI) GenBank. A set of sequences of 100 Malaysian samples aligned as 550 characters of the cytochrome c oxidase subunit I (cox1) and 706 characters of the II (cox2) genes revealed ten haplotypes (A1-A10) and eight haplotypes (B1-B8), respectively. The concatenated sequences of cox1 and cox2 genes with a total of 1256 characters revealed 15 haplotypes (AB1-AB15). Analyses indicated that haplotype AB1 was the most frequent and the most widespread haplotype in Malaysia. Overall haplotype and nucleotide diversities of the concatenated sequences were 0.52909 and 0.00424, respectively, with moderate genetic differentiation (FST = 0.17522) and high gene flow (Nm = 1.18). The western population presented the highest genetic diversity (Hd = 0.78333, Pi = 0.01269, Nh = 9), whereas the southern population demonstrated the lowest diversity (Hd = 0.15667, Pi = 0.00019, Nh = 3). The concatenated sequences showed genetic distances ranged from 0.08 % to 4.39 %. There were three aberrant haplotypes in cox2 sequences that highly divergent, suggesting the presence of cryptic species or occurrence of introgression. In the global point of view, the aligned sequences of C. felis revealed 65 haplotypes (AA1-AA65) by the cox1 gene (n = 586), and 27 haplotypes (BB1-BB27) by the cox2 gene (n = 204). Mapping of the haplotype network showed that Malaysian C. felis possesses seven unique haplotypes in both genes with the common haplotypes demonstrated genetic affinity with C. felis from Southeast Asia for cox1 and South America for cox2. The topologies of cox1 and cox2 phylogenetic trees were concordant with relevant grouping pattern of haplotypes in the network but revealed two major lineages by which Malaysian haplotypes were closely related with haplotypes from the tropical region.
  15. Chen CD, Low VL, Lau KW, Lee HL, Nazni WA, Heo CC, et al.
    J Am Mosq Control Assoc, 2013 Sep;29(3):243-50.
    PMID: 24199499
    The present study aims to investigate the susceptibility status of Aedes albopictus, Culex quinquefasciatus, and Cx. vishnui collected from a pig farm in Tanjung Sepat, Selangor, toward 11 insecticides representing the classes of organochlorines, carbamates, organophosphates, and pyrethroids. The results of a World Health Organization adult mosquito bioassay revealed that Ae. albopictus, Cx. quinquefasciatus, and Cx. vishnui exhibited different susceptibility toward various insecticides. Overall, pyrethroids were able to induce rapid knockdown for all test mosquito species. The pyrethroids lambdacyhalothrin and etofenprox were able to cause high mortality (> 80%) of all 3 species. The findings of the present study will benefit local authorities in selecting appropriate dosage of insecticides to be used in mosquito control in this area.
  16. Chen CD, Nazni WA, Lee HL, Hashim R, Abdullah NA, Ramli R, et al.
    Trop Biomed, 2014 Jun;31(2):381-6.
    PMID: 25134909 MyJurnal
    This study reported the ant species that were recovered from monkey carcasses in three different ecological habitats in Malaysia. The study was conducted from 9 May - 10 October 2007, 6 May - 6 August 2008 and 26 May - 14 July 2009 in forested area (Gombak, Selangor), coastal area (Tanjong Sepat, Selangor) and highland area (Bukit Cincin, Pahang), respectively. Monkey carcass was used as a model for human decomposition in this study. A total of 4 replicates were used in each of the study sites. Ants were observed to prey on eggs, larvae, pupae and newly emerged flies. This study found that ant species could be found at all stages of decomposition, indicating that ants were not a significant indicator for faunal succession. However, different species of ants were obtained from monkey carcasses placed in different ecological habitats. Cardiocondyla sp. was only found on carcasses placed in the coastal area; while Pheidole longipes, Hypoponera sp. and Pachycondyla sp. were solely found on carcasses placed in the highland area. On the other hand, Pheidologeton diversus and Paratrechina longicornis were found in several ecological habitats. These data suggests that specific ant species can act as geographic indicators for different ecological habitats in forensic entomology cases in Malaysia.
  17. Chen CD, Nazni WA, Lee HL, Norma-Rashid Y, Lardizabal ML, Sofian-Azirun M
    Trop Biomed, 2013 Jun;30(2):220-30.
    PMID: 23959487 MyJurnal
    Larvae of Aedes albopictus obtained from dengue endemic areas in Selangor, Malaysia were evaluated for their susceptibility to operational dosage of temephos (1 mg/L). Larval bioassays were carried out in accordance to modified WHO standard methods. Biochemical microassay of enzymes in Ae. albopictus was conducted to detect the emergence of insecticide resistance and to define the mechanisms involved in temephos resistance. The 50% mortality lethal time (LT50) for Ae. albopictus tested against temephos ranged between 58.65 to 112.50 minutes, with resistance ratio ranging from 0.75 - 1.45. This study addressed the fluctuation of time-related susceptibility status of Ae. albopictus towards insecticide. Significant difference on the weekly enzyme levels of non-specific esterases, mixed function oxidases and glutathione S-transferases was detected (p ≤ 0.05). No significant correlation was found between temephos resistance and enzyme activity (p > 0.05). Only glutathione S-transferases displayed high level of activity, indicating that Ae. albopictus may be resistant to other groups of insecticide. The insensitive acetylcholinesterase was detected in some field collected Ae. albopictus populations, indicating the possibility of emergence of carbamate or other organophosphate resistance in the field populations. Continuous resistance monitoring should be conducted regularly to confirm the efficacy of insecticides for dengue control.
  18. Chen CD, Lee HL, Nazni WA, Ramli R, Jeffery J, Sofian-Azirun M
    Trop Biomed, 2010 Aug;27(2):355-9.
    PMID: 20962738
    A study on insect succession of monkey carcass in a forested area in Ulu Gombak, Selangor, Malaysia was conducted from 9 May to 18 June 2007. The third instar of the housefly, Musca domestica (Linnaeus) (Diptera: Muscidae) were only found on dry stage of a decomposed (Day-33) monkey carcass (Macaca fascicularis Raffles). This observation revealed that M. domestica maggots were found together with other muscid fly maggots, Hydrotaea (=Ophyra) spinigera (Stein) (Diptera: Muscidae) on dry stage of a carcass. However, the role of M. domestica on forensic entomological study remains unknown. This study recorded the first finding of M. domestica maggots on primate carcass in Malaysia.
  19. Chen CD, Lee HL, Chan CK, Ang CL, Azahari AH, Lau KW, et al.
    Trop Biomed, 2009 Dec;26(3):360-5.
    PMID: 20237452
    The bioefficacy of nine commercial formulations of temephos against Aedes aegypti, Aedes albopictus and Culex quinquefasciatus larvae were evaluated in the laboratory. WHO larval bioassay with operational dosage of temephos at 1 mg/L was performed. The larval mortality was recorded every 5 minutes until complete mortality was achieved. All formulations of temephos exhibited various toxicity level against Ae. aegypti, Ae. albopictus and Cx. quinquefasciatus. Generally, larvae of Cx. quinquefasciatus was susceptible to all formulations of temephos, followed by Ae. aegypti and Ae. albopictus.
  20. Chen CD, Nazni WA, Lee HL, Sofian-Azirun M
    Trop Biomed, 2005 Dec;22(2):207-16.
    PMID: 16883289 MyJurnal
    Larvae obtained from Taman Samudera (Gombak, Selangor), Kampung Banjar (Gombak, Selangor), Taman Lembah Maju (Cheras, Kuala Lumpur) and Kampung Baru (City centre, Kuala Lumpur) were bioassayed with diagnostic dosage (0.012 mg/L) and operational dosage (1 mg/L) of temephos. All strains of Aedes aegypti and Aedes albopictus showed percentage mortality in the range of 16.00 to 59.05 and 6.4 to 59.50 respectively, after 24 hours. LT50 values for the 6 strains of Ae. aegypti and Ae. albopictus were between 41.25 to 54.42 minutes and 52.67 to 141.76 minutes respectively, and the resistance ratio for both Aedes species were in the range of 0.68 to 1.82 when tested with operational dosage, 1 mg/L temephos. These results indicate that Aedes mosquitoes have developed some degree of resistance. However, complete mortality for all strains were achieved after 24 hours when tested against 1 mg/L temephos.
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