The effectiveness of a floor gully with grating to prevent the oviposition of aedes (Stegomyia) aegypti (Linneaus): a laboratory study

This study was conducted to evaluate the effectiveness of a floor gully come with grating to prevent the oviposition of Aedes aegypti in the floor trap. In order to conduct the test, two containers were placed into a mosquito cage (30 cm × 30 cm × 30 cm). Both containers were filled with declorinated seasoned tap water and covered with floor gully c/w grating and normal floor gully, respectively. A total of 50 gravid Ae. aegypti females were then released into the cage and left for a week. All the eggs obtained from the test were allowed to remain inside the containers for the eggs to hatch. The number of hatched larvae was counted and recorded. Five replicates were conducted concurrently. There was a significant difference of Ae. aegypti larvae obtained between container with floor gully c/w grating and normal floor gully (p < 0.05). A total of 96.41% reduction of Ae. aegypti larvae was obtained in the container with floor gully c/w grating compared with the normal floor gully, indicating that the floor gully c/w grating used in this study was able to prevent oviposition of Ae. aegypti in holding water

Toxicity of imidacloprid gel bait against laboratory strain of Periplaneta americana (L.) (Dictyoptera : Blattidae) and Blattella germanica (L.)(Dictyoptera : Blattellidae)

The efficacy of a 2.15% imidacloprid gel bait against laboratory strain Periplaneta americana and Blattella germanica was evaluated under laboratory conditions. The susceptibility trend of both species towards imidacloprid was: adult male < adult female < nymphs. All stages of both species were dead within 10 days in primary poisoning testing. Periplaneta americana adult male (LT50 = 0.47 h; LT95 = 5.24 h) died fastest, while nymphs of B. germanica took the longest time to reach 95% mortality (LT95 = 43.84 h). In indirect exposure via secondary poisoning, only adult males of P. americana (LT50 = 100.63 h) and B. germanica (LT50 = 54.66 h) obtained 50% mortality before the testing ended. No complete mortalities were achieved in any stages of both species within 10 days of secondary poisoning testing. Therefore, imidacloprid gel bait used in this study was able to cause complete mortalities within less than 2 days of 10-day primary poisoning testing but less effective in the 10-day secondary poisoning testing

Susceptibility of Aedes albopictus skuse (Diptera: Culicidae) to permethrin in Kuala Lumpur, Malaysia

Background: Insects control using insecticides is used extensively and intensively in vector control programs in many countries including Malaysia. Because of this, mosquito species have been found to develop various levels of resistance towards these insecticides, leading to failure in vector control activities. Objectives: We determined permethrin resistance status in laboratory susceptible, permethrin-selected, and field strains of Aedes albopictus. Methods: The susceptibility status of laboratory susceptible strain, permethrin-selected strain, and four field strains of Aedes albopictus collected from Kuala Lumpur were determined using three standard laboratory tests, WHO larval bioassay, WHO adult mosquito bioassay, and microassay of mixed function oxidases (MFOs). Results: The LC50 values of permethrin-selected strain and field strains obtained from the WHO larval bioassay were almost two times higher (0.38-0.44 mg/L) than the LC50 value of the laboratory strain (0.20 mg/L). In the WHO adult bioassay, the susceptibility of permethrin-exposed of both permethrin-selected strain, and field strains (LT50 = 19.39 to 20.65 min) were reduced for 1.31 to 1.72 times after been exposed to the synergist, piperonyl butoxide (PBO) prior to permethrin. Complete mortalities were also recorded in both permethrin-exposed and PBO + permethrin-exposed Ae. albopictus of all strains, twenty-four hours post-exposure. For the MFOs enzyme microassay, a significant difference (p <0.05) in the mean absorbance of elevated oxidase activity at 630 nm was observed between all strains of both the non-exposed and PBO-exposed Ae. albopictus. Strong and significant positive correlations were also observed between LT50 values of permethrin-exposed and PBO + permethrinexposed with oxidase level in Ae. albopictus tested (r = 0.943; p <0.05). Conclusion: These results indicate the association of oxidase activity with permethrin resistance development in Ae. albopictus

Evaluating the efficacy of commercial Bacillus thuringiensis israelensis FOR Aedes albopictus LARVAL control in various land use

A commercial bacterial product of Bacillus thuringiensis israelensis (Bti); Mosquito BTI from USA was tested for its efficacy in exterminating the local populations of Aedes albopictus larvae. Larval surveys were carried out to obtain field populations of Ae. albopictus from various land use namely dengue-risk and dengue-free housing localities as well as agrarian localities like oil palm plantations, rubber estates and paddy fields. A 24-hour larval bioassay using Mosquito BTI was performed on each Ae. albopictus population. Only a maximum of 2.00% mortality was observed by the end of the first four hours of exposure while a maximum of 25.00% mortality was displayed at 24 hours of exposure. Results showed the potential use of Bti in reducing local Ae. albopictus larval populations but more than 24 hours may be required to achieve complete mortalities among these populations upon exposure to Bti. Some limitations of this study were also discusse

Dengue vector surveillance in major towns of Malaysia

Ovitrap surveillance was conducted between February and June 2017 to determine the abundance and distribution of dengue vectors in 13 residential areas located in major towns of different states in Malaysia. Forty ovitraps were placed randomly within the vicinity of buildings which were protected from sunlight and rain. The study revealed that ovitrap index (OI) ranged from 12.50% to 87.50% across all study sites. Both Aedes aegypti and Aedes albopictus were found breeding in all study sites except for the study sites in Alor Setar, Kedah Gambang, Pahang and Kuala Terengganu, Terengganu, Malaysia in which only Ae. albopictus was recorded. The mean number of larvae obtained revealed that Ae. albopictus was a more dominant dengue vector as compared to the mean number of Ae. aegypti larvae in nine out of thirteen study sites (P<0.05). Mixed breeding of both Aedes species were found in 4.00% to 28.57% of the total number of recovered ovitraps from all study sites. This study revealed that OIs obtained from all these major towns were >10%, indicating Malaysia is generally at risk of dengue outbreak, and control approaches must be carried out immediately to reduce the vector population to a level below the threshold of transmission

Breeding habitats of mosquito larvae in a paddy growing area in Kuala Pilah, Negeri Sembilan, Malaysia

Surveillance of mosquito larvae was performed in a paddy growing area in Kuala Pilah, Negeri Sembilan, Malaysia to uncover different types of breeding receptacles for mosquito larvae and species composition that bred in those positive receptacles. Fifty (50) natural and artificial receptacles were positive with mosquito breeding. About 96.00% of these positive receptacles were found outdoor. All positive indoor and most positive outdoor receptacles were conquered by Aedes albopictus Skuse while the rest were occupied by Culex quinquefasciatus Say. Population dynamics of Ae. albopictus in the study site should be constantly monitored and controlled to avoid the dispersal of mosquito-borne diseases such as dengue and chikungunya among local residents

Single and co-breeding of different mosquito species in fogging-free and dengue risk areas in west Malaysia

Ovitrap surveillance was carried out in fifteen localities encompassing fogging-free and dengue risk areas in West Malaysia to determine on the dispersal and prevalence of single and co-breeding of mosquito larvae particularly Aedes. Ovitraps were sited randomly indoors and outdoors within human settlements in all study areas. All the localities exhibited positive ovitraps with single breeding of Ae. albopictus that ranged between 64.29% and 100.00%. These findings indicated Ae. albopictus as the predominant container-breeding species in all study areas. The co-breeding of Ae. aegypti with Ae. albopictus larvae (34 ovitraps), Ae. albopictus with Culex quinquefasciatus larvae (32 ovitraps) as well as Cx. quinquefasciatus with Armigeres subalbatus larvae (1 ovitrap) were also detected in certain study localities. Interestingly, co-breeding of Ae. albopictus with Ar. subalbatus larvae as well as Ae. albopictus with Uranotaenia sp. larvae in Malaysia is reported for the first time in the present study. Better understanding of the co-breeding scenario involving different species of mosquito larvae is needed to ensure the efficacy of vector control actions to be conducted

Simulated field study on the efficacy of the thermal application of a synergized pyrethroid formulation against Aedes aegypti (Linn.) and Culex quinquefasciatus say

Thermal application of a synergized pyrethroid formulation containing 0.8% w/w s-bioallethrin, 18.7% w/w permethrin and 16.8% w/w piperonyl butoxide was performed to evaluate its efficacy against adult and larva of Aedes aegypti and Culex quinquefasciatus. Three cages each containing 15 mosquitoes and paper cups each containing 25 larvae in 250 ml of water were deployed at each test point between 3 and 20 feet. The formulation was diluted (formulation:water) 1:33, 1:50 and 1:100, respectively, and applied using a thermal fogger. Sixty minutes post spraying, the adult knock down rate of Ae. aegypti and Cx. quinquefasciatus at a maximum distance of 15 feet using all dilution ratios ranged from 96.67 – 100% and 43.33 – 100%, respectively. More than 70.00% adult mortalities were recorded for both mosquito species at the distance between 3 feet and 15 feet 24 hours post spraying. In contrast, complete larval mortalities of Ae. aegypti were obtained at a maximum distance of 10 feet with dilution ratio of 1:33, while more than 80.00% larval mortalities were observed for Cx. quinquefasciatus at similar maximum distance using all dilution ratios. These results showed that thermal application using synergized pyrethroid formulation was effective against both mosquito species tested especially the adult stage

Surveillance of aedes vectors in selected agricultural, fogging-free and dengue-prone areas in Peninsular Malaysia

Distributions of Aedes vectors in fifteen study sites comprising of ag-ricultural, fogging-free and dengue-prone areas in Peninsular Malaysia were investigated using ovitraps during January and May 2016 placed indiscriminately inside and outside human premises in all study sites. Cheras, Federal Territory of Kuala Lumpur, a dengue-prone area showed the highest ovitrap index (OI) (96.00%) while the lowest OI (64.00%) was found in both Padang Serai, Kedah and Temerloh, Pahang, fogging-free residential areas. Aedes albopictus was the most dominant species in all study sites while Ae. aegypti was captured in only five study sites. Mean number of larvae per recovered ovitrap among various species is significantly different for all types of areas except for oil palm planta-tions. The existence of Ae. aegypti in a few and Ae. albopictus in all study sites suggest their roles in the current and forthcoming transmission of dengue virus in these study sites. © 2019, SEAMEO TROPMED Network. All rights reserved

Mosquito Larval Surveillance in a Rice Field in Tanjung Karang, Selangor, Malaysia

Mosquito larval surveillance was carried out in a rice field in Tanjung Karang, Selangor, Malaysia to determine the diversity of breeding habitats of mosquito larvae and species composition of those mosquito larvae that bred in positive habitats within the study area. From 215 potential mosquito breeding habitats inspected, 93.90% outdoor containers and 6.10% indoor containers were positive with mosquito breeding. Artificial containers (71.95%) were favorable breeding habitats of mosquito larvae compared to natural containers (28.05%). Only Aedes albopictus Skuse (80.80%) and Culex quinquefasciatus Say (19.20%) larvae were collected from all positive breeding habitats. This result shows that Ae. albopictus is a predominant outdoor breeder in the study area and could also invade indoors. It is crucial to identify the mosquito species available in the study area and their habitats to ensure the effectiveness of vector control strategies conducted so that the transmission of any mosquito-borne diseases could be avoided or lessened