Evaluation of the effectiveness of Bacillus thuringiensis ssp. israelensis (B.t.i.) against mosquito larvae dispersed by ultralow volume (ULV) spraying was conducted in simulated field trials. Effectiveness was measured using 3 different indicators: larval mortality, colony-forming unit enumeration, and droplet analysis. B.t.i. was dispersed with a ULV generator using 2 different flow rates: 0.3 and 0.5 liter/min on 2 different days. Based on the results of this study, it can be concluded that an output of 0.3 liter/min is effective for controlling Aedes aegypti. although a dosage of 0.5 liter/min can be used when high residual activity is desired. For Culex quinquefasciatus control, both dosages were effective but with low residual activity. For Anopheles maculatus control, only a discharge rate of 0.5 liter/min was effective with low residual activity. B.t.i. application at both dosages penetrated tires well, indicating that B.t.i. ULV application is an effective method for controlling container-inhabiting mosquitoes. Good coverage of target area and penetration were attributed to satisfactory droplet profiles.
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.
Emulsifiable concentrates of DursbanR (chlorpyrifos) and Dowco 214 (chlorpyrifos-methyl) were tested as mosquito larvicides using Hudson knapsack sprayers on small plots of rice-fields on Penang Island. The mosquitoes found in these rice-fields are predominantly Anopheles campestris and Culex tritaeniorhynchus. At dosages of 14, 28 and 56 gm hectare-1, Dursban is effective in maintaining the rice-fields free of Anopheles larvae for at least 2, 3 and 7 days respectively. Dowco 214 at 56 gm hectare-1 is able to keep the fields free of all mosquito larvae for at least 2 days.
The safety of bacterial cells of Clostridium bifermentans serovar malaysia, which is highly toxic to mosquito larvae, was tested on mice, guinea pigs, rabbits, and goldfish. Inoculations of at least 1 x 10(8) cells per animal by routes recommended by World Health Organization (subcutaneous, percutaneous, inhalation, force-feeding, intraperitoneal, intravenous) and tests of subacute toxicity, anaphylactic shock, persistence in heart blood, and virulence by successive passages, were performed on mice, guinea pigs, or both. Growth was monitored for 1 mo before necropsy. Ocular irritation and skin scarification were tested with rabbits. C. bifermentans serovar malaysia did not induce any mortality or abnormal reactions in mammals at a dose 1,000 times higher than the level established by W.H.O. for the demonstration of safety. Bacterial cells are not toxic to goldfish at a dose 1,000 times higher than the LD50 for the target-mosquito larvae. We conclude that C. bifermentans serovar malaysia bacterial cells are safe for laboratory mammals and goldfish.
This study was conducted using the glass chamber method to determine the susceptibility status of the dengue vector, Aedes aegypti (L.) from 11 states in Malaysia to commercial mosquito coils containing four different active ingredients, namely metofluthrin, d-allethrin, d-trans allethrin, and prallethrin. Aedes aegypti exhibited various knockdown rates, ranging from 14.44% to 100.00%, 0.00% to 61.67%, 0.00% to 90.00%, and 0.00% to 13.33% for metofluthrin, d-allethrin, d-trans allethrin, and prallethrin, respectively. Overall, mortality rates ranging from 0.00% to 78.33% were also observed among all populations. Additionally, significant associations were detected between the knockdown rates of metofluthrin and d-allethrin, and between metofluthrin and d-trans allethrin, suggesting the occurrence of cross-resistance within pyrethroid insecticides. Overall, this study revealed low insecticidal activity of mosquito coils against Ae. aegypti populations in Malaysia, and consequently may provide minimal personal protection against mosquito bites.
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.
The effective control of Aedes mosquitoes using traditional control agents is increasingly challenging due to the presence of insecticide resistance in many populations of key mosquito vectors. An alternative strategy to insecticides is the use of toxic sugar baits, however it is limited due to short-term efficacy. Alginate-Gelatin hydrogel beads (AGHBs) may be an effective alternative by providing longer periods of mosquito attraction and control, especially of key vectors of dengue viruses such as Aedes aegypti and Aedes albopictus. Sodium alginate (ALG) and gelatin (GLN) are natural polymers, which can be a potential candidate to develop the AGHBs baits due to their biodegradability and environmental safety. Here we provide an assessment of the preparation of AGHBs optimized by varying the concentrations of ALG, GLN, and its cross-linking time (TIME). Fourier transform infrared spectroscopy (FTIR) analysis results in the determination of liquid bait loaded in the AGHBs. The evaluation of AGHBs' effectiveness as the potential baiting tool based on the mortality rate of mosquitoes after the bait consumption. The 100 % percent mortality of Aedes mosquitoes was obtained within 72 h of bait consumption. The field evaluation also justifies the applicability of AGHBs for outdoor applications. We conclude that the AGHBs are applicable as a baiting tool in carrying liquid bait in achieving mosquito mortality.
Among several vector control methods commonly used, environmental management is one of the control measures to mitigate dengue in such vulnerable communities. Since there is no curative treatment for dengue yet, targeted environmental and ecosystem management is increasingly relevant. Hence, this review was conducted to identify the effectiveness of environmental management intervention strategy to reduce dengue cases. We searched PUBMED, CENTRAL, SCOPUS, Web of Science, CIJE, WHO ICTRP, and ClinicalTrials.gov up to January 2021. A total of 521 articles were screened. Only 16 studies were included in this review. There were 6 studies that applied all three types of environmental management interventions (manipulation, modification and behavior), 8 studies applied two types of interventions (manipulation and behavior) and 2 studies applied one type of intervention (manipulation or behavior). All included studies reported reduction of Aedes entomological indices. The studies showed reduction in dengue cases and density of Aedes population through environmental interventions. It is recommended for the health authority to incorporate environmental management intervention in dengue control activities and enhanced the community involvement to ensure sustainability with high impact on dengue reduction.
Mosquitocidal strains of B. sphaericus serotype H-5a5b were shown for the first time to exhibit antagonistic activities against several human pathogens especially Salmonella. These strains of B. sphaericus also exhibited high larval toxicity against several mosquitoes.
Susceptibility status of Aedes aegypti (L.) and Aedes albopictus Skuse larvae obtained from 12 states in Malaysia were evaluated against five insect growth regulators (IGRs), namely, pyriproxyfen, methoprene, diflubenzuron, cyromazine, and novaluron under laboratory conditions. Field populations of Ae. aegypti exhibited moderate resistance toward methoprene and low resistance toward pyriproxyfen, with resistance ratios of 12.7 and 1.4, respectively, but susceptibility to diflubenzuron, cyromazine, and novaluron. On the other hand, field populations of Ae. albopictus exhibited low resistance against diflubenzuron and novaluron, with resistance ratio of 2.1 and 1.0, respectively, but susceptibility to other tested IGRs. Our study concluded that the tested IGRs provide promising results and can be used to control field population of Ae. aegypti and Ae. albopictus, especially cyromazine. The use of IGR should be considered as an alternative when larvae develop resistance to conventional insecticides.
1. Several experiments were carried out in the field and in the laboratory with various insecticides against A maculatus. 2. Almost all the mosquitoes that came into contact with surfaces sprayed with DDT preparations died in less than 30 hours but the length of life varied with the preparation and depended on various factors that are mentioned. Control mosquitoes lived almost twice as long. 3. Gammexane Dispersible Powder (P 520) killed in a much shorter time than the DDT preparations and holds out a greater hope of success in controlling ‘A maculatus’ malaria with insecticides. 4. It is difficult to assess the value of insecticides in any one year in areas where breeding of the vector is intense. The results of long term field experiments, under strict control, are awaited. 5. Meanwhile, Mass Suppression with drugs still remains the method of choice – in this area.