Currently, dengue fever is considered as the main health problem in several parts (Mekkah, Jeddah, Jazan and Najran) of Kingdom of Saudi Arabia (KSA) with dramatically increase in the number of cases reported every year. This is associated with obvious ineffectiveness in the recent control and management programs for the mosquito vector (Aedes aegypti). Here, we suggested promoting the health education and public awareness among Saudi people to improve the control of dengue mosquito vector. Several suggestions and recommendations were highlighted here to ensure effectiveness in the future control and management programs of dengue mosquito vector in KSA.
A field trial of the use of expanded polystyrene beads (EPSB) to control the breeding of mosquito larvae in household septic tanks was conducted in Sarawak. One week after treatment, the breeding of Culex quinquefasciatus and Aedes albopictus was reduced by 100% and 68.7% respectively. For both species combined, a 57.25% reduction in the adult emergence rate was achieved. No adult was caught in the emergence trap one month after treatment. A reduction in mosquito biting rates was reported by 87.3% of respondents. All households regarded the EPSB treatment as effective. This study has reduced the relatively high infestation rate of A. albopictus in the septic tanks to 16-20%. The EPSB treatment is feasible and practical. Post-treatment assessment using adult emergence traps and the implications for the vector control programme of the local authority are discussed.
The spraying of insecticide on foliage to provide an insecticidal barrier may serve as part of the vector control measures to combat the increasing threat of Aedes-borne diseases. The effectiveness of insecticide barrier spraying was evaluated by assessing the residual efficacy of deltamethrin sprayed on foliage against Malaysian Ae. aegypti (L.) and Ae. albopictus (Skuse). In this semi-field study, landscape plants grown within the vicinity of the Institute for Medical Research (IMR), Malaysia, were treated with deltamethrin suspension concentrate (SC) with the dosage of 30 mg/m2 and 50 mg/m2 in three rounds of spraying. Deltamethrin residual activity on treated and untreated leaves was investigated using standard WHO cone bioassays. Wild Aedes populations at both deltamethrin-treated and untreated plant clusters were monitored by ovitrap surveillance. Ovitrap monitoring revealed that the mean number of Ae. albopictus larvae at deltamethrin-treated were significantly lower than the mean number of larvae of the same species at the untreated plant cluster. Cone bioassay results showed that the insecticide remained effective for up to 4 weeks (> 80% mortality), but the insecticide residual activity was affected by rainfall. These results suggest that insecticide barrier spraying is a promising tool and may be used along with other mosquito control tools such as indoor residual spray and space spraying to reduce the dengue burden.
Fogging with insecticides is one of the main control measures for adult mosquito populations employed in countries that are affected by dengue. In many such countries, urban communities are increasingly characterised by high-density residence in high-rise condominia. Although fogging is typically applied at the ground level, its efficacy in three-dimensional urban environments is poorly understood. Here, we investigated the effect of fogging on vector mosquito distribution and abundance in high-rise condominia by conducting a before-after fogging survey. We showed that although mosquitoes were significantly concentrated at the lower levels in high-rise condominia, they were found throughout the three-dimensional environments. Fogging did not significantly alter this distribution or abundance pattern across any floor level. Thus, any fogging effect was short-lived as mosquito populations recovered within a few days before the subsequent scheduled treatment. In addition, increasing fogging frequency within practicable limits did not prolong the intended control effect. As urban mosquitoes are increasingly insusceptible to fogging due to insecticide resistance and vertical avoidance, this study demonstrates the need to implement other mosquito control strategies for high-rise condominia to manage mosquito populations.
A field evaluation on the effectiveness of a modified approach of chemical fogging of insecticides against the conventional method was carried out in the Seremban district within the state of Negeri Sembilan, Malaysia from 7th February 2003 to 7th September 2003. In the 3 months period, November 2002 to January 2003, prior to institution of modified approach of chemical fogging, 27 of 42 (64.3%) dengue outbreaks were successfully controlled within the stipulated time frame of 14 days by the conventional approach of thermal chemical fogging. However, during the period when the modified approach of chemical fogging was instituted, 25 of 27 (92.6%) dengue outbreaks within the same district were successfully controlled within the 14-days time-line. Statistically, the modified approach of chemical fogging significantly improved the success rate of achieving dengue outbreak control within the stipulated time frame (chi2 = 5.65, p = 0.01745). The modified approach of chemical fogging also appeared to reduce the number of dengue cases recorded in the same district. This small pilot study shows that the modified approach of chemical fogging reduced cost in carrying out each fogging activity to control dengue outbreak. It also substantially reduced the required time taken to complete each fogging activity in comparison to the conventional approach. Thus, it enabled similar number of workers to cover more localities simultaneously affected by the outbreaks. In addition, the modified approach reduced the exposure time to hazardous insecticides for each worker doing hand-held thermal fogging.
Comparative field efficacy studies of four mosquito coil formulations containing active ingredient of d-allethrin (0.19 or 0.28 w/w) and d-transallethrin (0.12 or 0.16% w/w) and blank coils without active ingredient were carried out in living rooms (mean size 54.1 m3) of residential houses in a squatter area in Butterworth, Malaysia. The major indoor biting mosquitos collected in the test site were that of Culex quinquefasciatus Say (84.7%). Mean percentage reduction of blank coils, coils with 0.19 and 0.28% d-allethrin and coils with 0.12 and 0.16% d-transallethrin were 29.0, 71.7, 70.9, 75.0 and 72.6%, respectively. The use of coils as a mean of personal protection against mosquitos is discussed.
Mating is a physiological process of crucial importance underlying the size and maintenance of mosquito populations. In sterile and incompatible insect technologies (SIT and IIT), mating is essential for mass production, persistence, and success of released individuals, and is a central parameter for judging the effectiveness of SIT/IIT programs. Some mosquitoes have an enormous reproductive potential for both themselves and pathogens and mating may contribute to persistence of infection in nature. As Aedes albopictus can transmit flaviviruses both sexually and horizontally, and as infected insects are usually derived from laboratory colonies, we investigated the implications of mating between a long-term laboratory colony of Ae. albopictus and wild populations.
A field trial was carried out to study the effect of lambdacyhalothrin on Anopheles maculatus in trap huts in Jeram Kedah, Negeri Sembilan, Malaysia. Two trap huts were built, of which one was sprayed with lambdacyhalothrin at a dosage of 25 mg ai/m2 and the other served as control. Eight collectors commenced collecting mosquitos from 1900 to 2400 hours, two each indoors and outdoors. Bioassay was also carried out in the treated and control huts to determine susceptibility of adult mosquitos to lambdacyhalothrin. In the treated hut more mosquitos were present during the pre- spraying period. Lambdacyhalothrin gave a mortality of 100% against An. maculatus for 8 months.
The measurement of the ultimate effects of the microbial insecticides on mosquito density is best obtained by assessment of adult populations. The main aims of this study are: (1) to assess the effect of Bacillus thuringiensis israelensis (Bti) FC Skeetal and Bactimos briquettes on the emergence rate of Mansonia bonneae developed from the introduced first-instar stage larvae and (2) to measure the effect of these two formulations of insecticides on Mansonia adult populations emerging from the natural breeding plots. Bti Skeetal and Bactimos briquettes at the lower applied dosages of 2.3 kg/ha and 1 briquette case/20 m2 respectively achieved 39-40% pupation rates and 31.5-34.2% adult emergence rates. At these low applied dosages, there was little or no direct effect on pupation from the surviving larvae and thereafter on the emergence of adults from the pupae. A two-fold increase in dosage, however, produced a drastic decline in the pupation rate and adult emergence rate. The rates dropped to 6.5% (pupation) and 4.3% (adult emergence) of the total larvae for Bactimos briquettes and to merely 1.5% (pupation) and 1.3% (adult emergence) of the total larvae for Skeetal. In studying the effect of Bti on the field populations of Mansonia mosquitos, two plots each were treated with Bactimos at 1 briquette case/10 m2 and Skeetal at 4.6 kg/ha. A wooden pyramid-shaped screened cage was placed on a cluster of host plants for a period of 2 weeks to trap the emerging adult mosquitoes. There were a total of 24 clusters of host plants in each plot.(ABSTRACT TRUNCATED AT 250 WORDS)
The pathogenicity of Bacillus sphaericus strain 1593 was tested against laboratory-reared larvae of four local species of mosquitoes of public health importance in Malaysia; Aedes aegypti, Anopheles balabacensis, Mansonia uniformis and Culex quinquefasciatus. The bacteria was shake-cultured at 28 +/- 1 degrees C for three days, using Glucose-Yeast Extract Salts medium. After which, the spores and vegetative cells were harvested and stored at 4 degrees C before use. Conditions for bioassays were mean temperature of 25 +/- 1 degrees C and relative humidity 65 +/- 5.0. Twenty third-instar larvae of each species were assayed in 90 ml of diluted spore solution. Each concentration and a control were replicated three times for each bioassay. Larval mortalities at 24 hours and 48 hours were taken and analyzed through Probit Analysis using a computer (IBM 370). LC50 values after 48 hours of exposure showed an increasing order of larval susceptibility as follows: Ae. aegypti (417.70 x 10(4)), An. balabacensis (45.84 x 10(4)), Ma. uniformis (18.23 x 10(4)) and Cx. quinquefasciatus (4.14 x 10(4) spores/ml). With the ability to kill 90% of the Cx. quinquefasciatus larvae tested with just a concentration of 10(5) spores/ml, B. sphaericus (strain 1593) has shown good potential as a biocontrol agent for this species of mosquito.
Bacillus thuringiensis israeliensis (BTI) against culicine mosquitoes was tried out in cement sullage drains in Kelang municipal area at a dosage of 0.15 ppm. and 0.6 ppm. The results of the trial showed that at 0.15 ppm. the BTI was not effective, but at 0.6 ppm. it was effective giving about 95% kill. There was no residual effect and treatment had to be repeated weekly.
Adulticidal and larvicidal performances of a water-based pyrethroid microemulsion Pesguard PS 102 (AI d-allethrin and d-phenothrin, both at 5.0% w/w) and Vectobac 12AS, an aqua-suspension Bacillus thuringiensis israelensis (B.t.i.) formulation (AI 1,200 ITU/mg) were assessed against mosquitoes Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus using a Leco ULV Fog Generator Model 1600 and a Scorpion 20 ULV AirBlast Sprayer. Laboratory-cultured mosquito adults and larvae were used for efficacy assessment. For trials using Leco, both pyrethroid and bacterial formulations were dispersed both singly and in combination with Pesguard PS 102 at a dosage of 0.2 liters/ha and B.t.i. at a dosage of 1.0 liter/ha. Similar trials with the Scorpion were also conducted with Pesguard PS 102 at a dosage of 0.2 liters/ha and a higher dosage of B.t.i. (1.5 liters/ha). Experiments were conducted in a football field (200 x 100 m) where five check points at 10, 25, 50, 75, and 100 m downwind from the spray nozzle were chosen for efficacy assessments. Knockdown and mortality were scored at 1 and 24 h postspraying. Results from both trials showed that mortality values varied with distance from spray nozzle. For trials with Leco, fogging with the combination of Pesguard PS 102 and B.t.i. provided larvicidal mortality of > 80% for both Aedes species and of > 60% for Cx. quinquefasciatus larvae at several check points, depending on wind conditions. Complete mortality of adult Aedes mosquitoes at 24 h posttreatment was also achieved, while mortality values for Culex adults reached > 90% under strong wind conditions. As for trials with the Scorpion 20, high adult and larval mortalities were also achieved, with > 90% mortality at some check points. The above study demonstrated the possibility of achieving both larvicidal and adulticidal effects when using a combination of B.t.i. and Pesguard PS 102 in ULV space spray.