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Study on the neurotoxicity of the temephos impregnated kenaf cellulose nanofiber (KCNF+T) aerosols against the female Aedes aegypti mosquitoes

Sabri N, Kamaldin J, Sivanathan M, Rasli R

Trop Biomed, 2024 Sep 01;41(3):283-289.
PMID: 39548782 DOI: 10.47665/tb.41.3.008

The study has generated visible aerosols with the diameter of 11 to 35 µm from the kenaf cellulose nanofiber (KCNF) impregnated with the temephos (KCNF+T) in water suspension. The study aimed to determine whether the KCNF+T aerosols are capable to elicit neurotoxicity in the adult mosquitoes via the respiratory exposure route by observing their behavioural response and measuring its body acetylcholine esterase (AChE) activity. Adult Aedes aegypti mosquitoes were assigned to one negative control group and three treatment groups namely, distilled water (vehicle control), KCNF and KCNF+T. The study adopted the MS1911 whereby the aerosols generated are released into the insecticide bioassay glass chamber (IBGC) separately to achieve four different aerosols concentrations of 6.4 ml/m3, 12.8 ml/m3, 19.2 ml/m3, and 25.6 ml/m3. Then the 20 sugar-fed mosquitoes were released free-flying into each IBGC to observe its behavioural response (knockdown) at 30, 60, 120, 180, 240, 300 minutes intervals and 24th hour mortality. Results showed that only mosquitoes exposed to KCNF+T aerosols exhibited persistent knockdown. There was significant difference (p< 0.05) between observation intervals with the cumulative knockdown of 84.8%, 92.8%, 99.0%, 100.0%, 100.0%, 100.0% compared with the KCNF aerosols. Further, it was distinctive that only KCNF+T is capable to cause the female mosquitoes moribund/mortality at the 24th hour with 90% at the lowest aerosol concentration of 6.4 ml/m3. The neuroenzyme assay on the mosquito that died from the KCNF+T exposure verified to have reduced AChE enzyme activity. The behavioural response and reduction of the AChE activity strongly suggests the temephos from the KCNF+T aerosols has been released into the mosquito body causing the neurotoxicity but KCNF alone is not neurotoxic.
Fulltext Entomological Surveillance Associated with Human Zika Cases in Miri Sarawak, Malaysia

Ali R, Azmi RA, Wasi Ahmad N, Abd Hadi A, Muhamed KA, Rasli R, et al.

Am J Trop Med Hyg, 2020 May;102(5):964-970.
PMID: 32228777 DOI: 10.4269/ajtmh.19-0339

Two confirmed human cases of Zika virus (ZIKV) were reported in the district of Miri, Sarawak, in 2016. Following that, a mosquito-based ZIKV surveillance study was conducted within 200-m radius from the case houses. Mosquito surveillance was conducted using five different methods, that is, biogents sentinel mosquito (BG) sentinel trap, modified sticky ovitrap, resting catch, larval surveillance, and conventional ovitrap. A total of 527 and 390 mosquito samples were obtained from the case houses in two localities, namely, Kampung Lopeng and Taman Shang Ri La, Miri, Sarawak, respectively. All mosquitoes collected were identified, which consisted of 11 species. Aedes albopictus, both the adult and larval stages, was the dominant species. Resting catch method obtained the highest number of adult mosquitoes (67%), whereas ovitrap showed the highest catch for larval mosquitoes (84%). Zika virus was detected in both adults and larvae of Ae. albopictus together with adults of Culex gelidus, and Culex quinquefasciatus using the real-time reverse transcriptase polymerase chain reaction (PCR) technique. It was noteworthy that Ae. albopictus positive with ZIKV were caught and obtained from four types of collection method. By contrast, Cx. gelidus and Culex quinquefasciatus adults collected from sticky ovitraps were also found positive with ZIKV. This study reveals vital information regarding the potential vectors of ZIKV and the possibility of transovarian transmission of the virus in Malaysia. These findings will be essentials for vector control program managers to devise preparedness and contingency plans of prevention and control of the arboviral disease.
Fulltext Insecticide resistance in dengue vectors from hotspots in Selangor, Malaysia

Rasli R, Cheong YL, Che Ibrahim MK, Farahininajua Fikri SF, Norzali RN, Nazarudin NA, et al.

PLoS Negl Trop Dis, 2021 Mar;15(3):e0009205.
PMID: 33755661 DOI: 10.1371/journal.pntd.0009205

BACKGROUND: In Malaysia, dengue remains a top priority disease and usage of insecticides is the main method for dengue vector control. Limited baseline insecticide resistance data in dengue hotspots has prompted us to conduct this study. The present study reports the use of a map on the insecticide susceptibility status of Aedes aegypti and Aedes albopictus to provide a quick visualization and overview of the distribution of insecticide resistance.
METHOD AND RESULTS: The insecticide resistance status of Aedes populations collected from 24 dengue hotspot areas from the period of December 2018 until June 2019 was proactively monitored using the World Health Organization standard protocol for adult and larval susceptibility testing was conducted, together with elucidation of the mechanisms involved in observed resistance. For resistance monitoring, susceptibility to three adulticides (permethrin, deltamethrin, and malathion) was tested, as well as susceptibility to the larvicide, temephos. Data showed significant resistance to both deltamethrin and permethrin (pyrethroid insecticides), and to malathion (organophosphate insecticide) in all sampled Aedes aegypti populations, while variable resistance patterns were found in the sampled Aedes albopictus populations. Temephos resistance was observed when larvae were tested using the diagnostic dosage of 0.012mg/L but not at the operational dosage of 1mg/L for both species.
CONCLUSION: The present study highlights evidence of a potential threat to the effectiveness of insecticides currently used in dengue vector control, and the urgent requirement for insecticide resistance management to be integrated into the National Dengue Control Program.

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