Evaluation of insecticide resistance among Malaysian Aedes albopictus Skuse larvae based on revised diagnostic doses of larvicides.

The susceptibility levels of Malaysian Aedes albopictus larvae sampled from several agricultural, fogging-free residential and dengue prone residential areas against different larvicides were evaluated using revised diagnostic doses derived from the 2xLC99 values of the reference strain. Upon 24-hour recovery period of WHO larval bioassay, incipient resistance was observed among Ae. albopictus larvae from rubber estates against fenitrothion (96.67% mortality) and permethin (97.00% mortality) while Ae. albopictus larvae from rice cultivation areas were moderately resistant to fenthion (94.33% mortality). Aedes albopictus larvae from dengue prone residential areas developed moderate to high resistance against dichlorodiphenyltrichloroethane (DDT), fenitrothion, fenthion, propoxur and permethrin (79.67% - 97.33% mortality). Moderate to high resistance were also demonstrated among all populations of Ae. albopictus larvae against temephos and chlorpyrifos (63.00% - 97.67% mortality). Except for Ae. albopictus larvae from oil palm plantations, all Ae. albopictus larval populations were also highly resistant to bendiocarb (65.67% - 89.67% mortality). Cross resistance between larvicides from similar and different insecticide classes were also revealed in this study. The use of revised diagnostic doses established from the local reference strain could reduce the possibility of underestimation or overestimation of the insecticide susceptibility status of field strain populations.

Evaluation of insecticide resistance among Malaysian Aedes albopictus Skuse larvae based on revised diagnostic doses of larvicides

@#The susceptibility levels of Malaysian Aedes albopictus larvae sampled from several agricultural, fogging-free residential and dengue prone residential areas against different larvicides were evaluated using revised diagnostic doses derived from the 2xLC99 values of the reference strain. Upon 24-hour recovery period of WHO larval bioassay, incipient resistance was observed among Ae. albopictus larvae from rubber estates against fenitrothion (96.67% mortality) and permethin (97.00% mortality) while Ae. albopictus larvae from rice cultivation areas were moderately resistant to fenthion (94.33% mortality). Aedes albopictus larvae from dengue prone residential areas developed moderate to high resistance against dichlorodiphenyltrichloroethane (DDT), fenitrothion, fenthion, propoxur and permethrin (79.67% – 97.33% mortality). Moderate to high resistance were also demonstrated among all populations of Ae. albopictus larvae against temephos and chlorpyrifos (63.00% – 97.67% mortality). Except for Ae. albopictus larvae from oil palm plantations, all Ae. albopictus larval populations were also highly resistant to bendiocarb (65.67% – 89.67% mortality). Cross resistance between larvicides from similar and different insecticide classes were also revealed in this study. The use of revised diagnostic doses established from the local reference strain could reduce the possibility of underestimation or overestimation of the insecticide susceptibility status of field strain populations.

Statewide Efficacy Assessment of Insect Growth Regulators Against Aedes albopictus (Diptera: Culicidae) in Sabah, Malaysia: An Alternative Control Strategy?

The efficacy of three groups of insect growth regulators, namely juvenile hormone mimics (methoprene and pyriproxyfen), chitin synthesis inhibitors (diflubenzuron and novaluron), and molting disruptor (cyromazine) was evaluated for the first time, against Aedes albopictus Skuse (Diptera: Culicidae) larvae from 14 districts in Sabah, Malaysia. The results showed that all field populations of Ae. albopictus were susceptible towards methoprene, pyriproxyfen, diflubenzuron, novaluron, and cyromazine, with resistance ratio values ranging from 0.50-0.90, 0.60-1.00, 0.67-1.17, 0.71-1.29, and 0.74-1.07, respectively. Overall, the efficacy assessment of insect growth regulators in this study showed promising outcomes and they could be further explored as an alternative to conventional insecticides.

Bioefficacy of mosquito mat vaporizers and associated metabolic detoxication mechanisms in Aedes aegypti (Linnaeus) in Selangor, Malaysia: A statewide assessment.

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.

Assessment of the susceptibility status of Aedes albopictus (Diptera: Culicidae) from Interior, Sandakan and Tawau divisions of Sabah, Malaysia based on WHO diagnostic doses of larvicides.

Susceptibility status of Aedes albopictus (Skuse) sampled from residential areas in Interior, Sandakan and Tawau divisions of Sabah, Malaysia, was evaluated based on the WHOrecommended doses of organochlorine and organophosphate larvicides. To determine susceptibility status, larval bioassays were carried out and post 24-hour mortalities based on WHO resistance classifications were adopted. The results demonstrated that Ae. albopictus larvae were resistant toward 5 out of the 8 larvicides tested. Larvae from all populations were resistant against bromophos, fenitrothion, malathion, temephos and dichlorodiphenyltrichloroethane (DDT), with mortalities ranging from 0.00 to 89.33%. Dieldrin, on the other hand, could induce 100.00% mortalities in all populations, followed by fenthion and chlorpyrifos, with mortalities ranging from 97.33 to 100.00% and 81.33 to 100.00% respectively. Despite most populations exhibiting similitude in their resistance status, larvae from Sandakan exhibited the highest resistance level whereas the lowest level was observed in Keningau. In view of the inadequacy of some larvicides in controlling Ae. albopictus in this study, integrated management such as insecticide rotation or combination of interventions is warranted.

Bioefficacy of mosquito mat vaporizers and associated metabolic detoxication mechanisms in Aedes aegypti (Linnaeus) in Selangor, Malaysia: A statewide assessment

@#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.

Assessment of the susceptibility status of Aedes albopictus (Diptera: Culicidae) from Interior, Sandakan and Tawau divisions of Sabah, Malaysia based on WHO diagnostic doses of larvicides

@# Susceptibility status of Aedes albopictus (Skuse) sampled from residential areas in Interior, Sandakan and Tawau divisions of Sabah, Malaysia, was evaluated based on the WHOrecommended doses of organochlorine and organophosphate larvicides. To determine susceptibility status, larval bioassays were carried out and post 24-hour mortalities based on WHO resistance classifications were adopted. The results demonstrated that Ae. albopictus larvae were resistant toward 5 out of the 8 larvicides tested. Larvae from all populations were resistant against bromophos, fenitrothion, malathion, temephos and dichlorodiphenyltrichloroethane (DDT), with mortalities ranging from 0.00 to 89.33%. Dieldrin, on the other hand, could induce 100.00% mortalities in all populations, followed by fenthion and chlorpyrifos, with mortalities ranging from 97.33 to 100.00% and 81.33 to 100.00% respectively. Despite most populations exhibiting similitude in their resistance status, larvae from Sandakan exhibited the highest resistance level whereas the lowest level was observed in Keningau. In view of the inadequacy of some larvicides in controlling Ae. albopictus in this study, integrated management such as insecticide rotation or combination of interventions is warranted.

Descriptions of the female, male and mature larva of Simulium contractum Takaoka (Diptera: Simuliidae) from Sulawesi, Indonesia.

Simulium (Simulium) contractum Takaoka from Sulawesi, Indonesia was known only as the pupa. Its female, male and mature larva are described for the first time. The tentative assignment of this species in the Simulium dumogaense species-group is confirmed by the adult characters including the female and male genitalia. The female and male of this species are similar to those of Simulium (Simulium) tumpaense Takaoka and Roberts but are distinguished by the yellowish femora.

Morphological characteristics of microfilariae in blood smears of the common treeshrew Tupaia glis (Mammalia: Scandentia) in Gemas, Negeri Sembilan, Malaysia

@#Some filarial nematodes, such as Wuchereria bancrofti, Brugia malayi, and Brugia timori, cause lymphatic diseases in humans in the tropics, whereas other filarial parasites from wild animals cause zoonotic diseases in humans worldwide. To elucidate the prevalence and diversity of filarial parasites in Malaysia, we investigated the filarial parasites from wild animals in Gemas, Negeri Sembilan. To find adult filarial parasites, we dissected 26 animals, which included five frogs, one skink, one snake, two birds, six common treeshrews, and 11 rats. Then, we examined microfilariae in the blood smears and skin snips obtained from each animal. We found two types of microfilariae in the blood smears of common treeshrews: one was very similar to Malayfilaria sofiani and the other closely resembled Brugia tupaiae. These findings indicate an additional distribution of these filarial parasites in Gemas.

Descriptions of the female, male and mature larva of Simulium contractum Takaoka (Diptera: Simuliidae) from Sulawesi, Indonesia

@#Simulium (Simulium) contractum Takaoka from Sulawesi, Indonesia was known only as the pupa. Its female, male and mature larva are described for the first time. The tentative assignment of this species in the Simulium dumogaense species-group is confirmed by the adult characters including the female and male genitalia. The female and male of this species are similar to those of Simulium (Simulium) tumpaense Takaoka & Roberts but are distinguished by the yellowish femora.

Insight into the origin of chikungunya virus in Malaysian non-human primates via sequence analysis.

Chikungunya virus (CHIKV) is maintained in the sylvatic cycle in West Africa and is transmitted by Aedes mosquito species to monkeys. In 2006, four verified CHIKV isolates were obtained during a survey of arboviruses in monkeys (Macaca fascicularis) in Pahang state, Peninsular Malaysia. RNA was extracted from the CHIKV isolates and used in reverse transcription polymerase chain reactions (RT-PCR) to amplify PCR fragments for sequencing. Nucleic acid primers were designed to generate overlapping PCR fragments that covered the whole viral sequence. A total of 11,238 base pairs (bp) corresponding to open reading frames (ORFs) from our isolates and 47 other registered isolates in the National Center for Biotechnology Information (NCBI) were used to elucidate sequences, amino acids, and phylogenetic relationships and to estimate divergence times by using MEGA 7.0 and the Bayesian Markov chain Monte Carlo method. Phylogenetic analysis revealed that all CHIKV isolates could be classified into the Asian genotype and clustered with Bagan Panchor clades, which are associated with the chikungunya outbreak reported in 2006, with sequence and amino acid similarities of 99.9% and 99.7%, respectively. Minor amino acid differences were found between human and non-human primate isolates. Amino acid analysis showed a unique amino acid at position 221 in the nsP1region, at which a glycine (G) was found only in monkey isolates, whereas arginine (R) was found at the same position only in human isolates. The time to the most recent common ancestor (MRCA) estimation indicated that CHIKV probably started to diverge from human to non-human primates in approximately 2004 in Malaysia. The results suggested that CHIKV in non-human primates probably resulted from the spillover of the virus from humans. The study will be helpful in understanding the movement and evolution of CHIKV in Malaysia and globally.

Adulticide Resistance Status of Aedes albopictus (Diptera: Culicidae) in Sabah, Malaysia: A Statewide Assessment.

Resistance status of Aedes albopictus (Diptera: Culicidae) collected from Sabah, East Malaysia, was evaluated against four major classes of adulticides, namely pyrethroid, carbamate, organochlorine, and organophosphate. Adult bioassays conforming to WHO standard protocols were conducted to assess knockdown and mortality rates of Ae. albopictus. Among tested pyrethroid adulticides, only cyfluthrin, lambda-cyaholthrin, and deltamethrin were able to inflict total knockdown. The other adulticide classes mostly failed to cause any knockdown; the highest knockdown rate was only 18.33% for propoxur. With regards to mortality rate, Ae. albopictus was unanimously susceptible toward all pyrethroids, dieldrin, and malathion, but exhibited resistance toward bendiocarb, propoxur, dichlorodiphenyltrichloroethane, and fenitrothion. Additionally, correlation analysis demonstrated cross-resistance between bendiocarb and propoxur, and malathion and propoxur. In conclusion, this study has disclosed that pyrethroids are still generally effective for Aedes control in Sabah, Malaysia. The susceptibility status of Ae. albopictus against pyrethroids in descending order was cyfluthrin > lambda-cyhalothrin > deltamethrin > etofenprox > permethrin.

Preliminary dengue vector surveillance in the Sunda Islands, Indonesia: Interchange of breeding habitat preferences of Aedes aegypti and Aedes albopictus.

Ovitrap surveillance was conducted to determine the infestation patterns of dengue vectors in fourteen study sites across eight provinces located in the Sunda Islands, Indonesia. High ovitrap indices up to 70% and 90% were obtained from indoor and outdoor areas, respectively. Mean numbers of Ae. aegypti and Ae. albopictus larvae ranged from 0.13 to 14.50 and 0.10 to 18.60, respectively. Mixed infestation (<10%) and interchange of breeding habitat preferences of Ae. albopictus and Ae. aegypti were also observed in the present study.

A new species of the Simulium (Simulium) crocinum species-group (Diptera: Simuliidae) from Vietnam.

A new black fly species, Simulium yukawai, is described on the basis of one female and its pupal exuviae from Vietnam. This new species is placed in the S. crocinum species-group of Simulium (Simulium) (Diptera: Simuliidae). It is characterized in the female by the paraproct covered with 48-50 distinct hairs on its ventral and lateral surfaces, and in the pupa by the frons and most of the thorax bare, gill with six dark filaments in three pairs closely arising from the base, of which the two outer filaments of the dorsal and middle pairs are much longer than other filaments, abdomen with distinct spine-combs on the dorsal surface of segments 7-9, and cocoon wall-pocket shaped, with a large anterolateral window on each side. Taxonomic notes are given to separate this new species from related species. This species is the fourth member of the S. crocinum species-group known from Vietnam.

Risk factors associated with flea infestation on cats.

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.

Monitoring Insecticide Resistance Profiles of Aedes aegypti (Diptera: Culicidae) in the Sunda Islands of Indonesia Based on Diagnostic Doses of Larvicides.

This study was conducted to monitor the susceptibility status of Aedes aegypti (Linnaeus) larvae in the Sunda Islands of Indonesia against various organophosphates and organochlorines. Larval bioassay was performed in accordance with the World Health Organization standard protocol. Field-collected and reference strains of Ae. aegypti larvae were tested against diagnostic doses of eight larvicides belonging to organophosphates and organochlorines, namely bromophos (0.050 mg/liter), chlopyrifos (0.002 mg/liter), fenitrothion (0.020 mg/liter), fenthion (0.025 mg/liter), malathion (0.125 mg/liter), temephos (0.012 mg/liter), DDT (0.012 mg/liter), and dieldrin (0.025 mg/liter). Mortality rates of larvae were recorded at 24-h posttreatment. This study showed that Ae. aegypti larvae from Padang, Samarinda, Manggarai Barat, and South Central Timor were susceptible to both fenitrothion and dieldrin (mortality rates ≥ 98%). About 6 out of 10 field strains of Ae. aegypti larvae were resistant (<80% mortality rates) against fenthion, whereas Ae. aegypti larvae from Kuningan, Samarinda, Sumba, and South Central Timor exhibited some degrees of resistance (mortality rates 80-98%). All field-collected Ae. aegypti larvae were resistant against diagnostic doses of chlorpyrifos, malathion, temephos, and DDT with mortality rates ranging from 0 to 74.67%. Continued insecticide susceptibility studies are essential to identify the efficacy of insecticides for an improved dengue vector control and to delay the development of insecticide resistance.

Risk factors associated with flea infestation on cats

@#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.

A new species of the Simulium (Simulium) crocinum species-group (Diptera: Simuliidae) from Vietnam

@#A new black fly species, Simulium yukawai, is described on the basis of one female and its pupal exuviae from Vietnam. This new species is placed in the S. crocinum species-group of Simulium (Simulium) (Diptera: Simuliidae). It is characterized in the female by the paraproct covered with 48–50 distinct hairs on its ventral and lateral surfaces, and in the pupa by the frons and most of the thorax bare, gill with six dark filaments in three pairs closely arising from the base, of which the two outer filaments of the dorsal and middle pairs are much longer than other filaments, abdomen with distinct spine-combs on the dorsal surface of segments 7–9, and cocoon wall-pocket shaped, with a large anterolateral window on each side. Taxonomic notes are given to separate this new species from related species. This species is the fourth member of the S. crocinum species-group known from Vietnam.

Preliminary dengue vector surveillance in the Sunda Islands, Indonesia: Interchange of breeding habitat preferences of Aedes aegypti and Aedes albopictus

@#Ovitrap surveillance was conducted to determine the infestation patterns of dengue vectors in fourteen study sites across eight provinces located in the Sunda Islands, Indonesia. High ovitrap indices up to 70% and 90% were obtained from indoor and outdoor areas, respectively. Mean numbers of Ae. aegypti and Ae. albopictus larvae ranged from 0.13 to 14.50 and 0.10 to 18.60, respectively. Mixed infestation (<10%) and interchange of breeding habitat preferences of Ae. albopictus and Ae. aegypti were also observed in the present study.

Bioefficacy Evaluation of Commercial Mosquito Coils Containing Metofluthrin, d-Allethrin, d-Trans Allethrin, and Prallethrin Against Aedes albopictus (Diptera: Culicidae) in Malaysia.

The bioefficacy of commercial mosquito coils containing four different active ingredients, namely metofluthrin, d-allethrin, d-trans allethrin, and prallethrin against Aedes albopictus (Skuse) (Diptera: Culicidae) from 10 states in Malaysia, was evaluated using the glass chamber method. In this study, Ae. albopictus exhibited various knockdown rates (50% knockdown time, KT50), ranging from 2.50 to 5.00 min, 2.50 to 7.00 min, 3.00 to 8.00 min, and 5.00 to 17.00 min for metofluthrin, d-trans allethrin, d-allethrin, and prallethrin, respectively. Overall, all strains of Ae. albopictus were most susceptible to metofluthrin, with mortality rates >80%. On the other hand, mortality rates ranging from 5.0 to 100% were observed from all populations exposed to d-trans allethrin, d-allethrin, and prallethrin. In addition, significant correlations between KT50 of metofluthrin and d-allethrin (r = 0.758, P = 0.011), metofluthrin and prallethrin (r = 0.676, P = 0.032), d-allethrin and d-trans allethrin (r = 0.832, P = 0.003), d-allethrin and prallethrin (r = 0.921, P = 0.000), and d-trans allethrin with prallethrin (r = 0.941, P = 0.000) were detected, suggesting some levels of cross-resistance within the pyrethroid insecticides. This study demonstrated that metofluthrin can induce high insecticidal activity in Ae. albopictus in Malaysia, followed by d-trans allethrin, d-allethrin, and prallethrin.