Using seven methods of surveillance, 58 species of mosquitoes from nine genera were in Pantai and the two neighbouring villages during two visits in 1982. Ma. bonneae was the most prevalent species attracted to man. In the forest shade Ma. bonneae and Ma. dives showed activity throughout the 24 hours with peak biting during 1900-2100 hours. An. balabacensis exhibited peak activity shortly after midnight. Inside and outside house, Ma. bonneae showed similar activity except that it ceased during the day. Mansonia was only mildly zoophilic. CDC light traps gave poor yields of mosquitoes. Pyrethrum spray catch inside houses early morning did not include any Mansonia. Outdoor day resting catch included Ma. bonneae fed on man. Transmission of Brugia, probably human filariasis, by Ma. bonneae occurred in Pantai and in the two neighbouring villages. One infection in Ma. dives was found in Pantai. The monthly infective biting rate and monthly transmission potential for Ma. bonneae were estimated at the forest shade and outside the house in Pantai.
Two highly active synthetic pyrethroid insecticides, lambdacyhalothrin and cypermethrin, were evaluated as thermal fogs against houseflies (Musca domestica Linnaeus) and mosquitos (Aedes aegypti Linnaeus). Lambdacyhalothrin (OMS 3021) showed an average of 2.5 times more knockdown activity and over 5 times more adulticidal activity than cypermethrin against Musca domestica and Aedes aegypti. These results demonstrate that lambdacyhalothrin is highly effective at very low rates as a thermal fog against Ae. aegypti and M. domestica. Commercially available formulations of 2.5% and 5% lambdacyhalothrin can be diluted either with water for ULV cold aerosol space-spraying or with diesel/kerosene for thermal fogging at recommended application rates of 0.5-1 g ai/ha for mosquito control and 2 g ai/ha for housefly control. Due to the very low rates of application, formulated products of lambdacyhalothrin are unlikely to present any acute hazards in normal use. The low dosages required to bring about rapid control of houseflies and mosquitos make this new pyrethroid insecticide particularly cost-effective. Coupled with its good residual activity (Jutsum et al, 1984), lambdacyhalothrin can be adopted as a powerful tool in integrated pest management program for the control of medically important pests and vectors.
A nationwide screening program searching for microbial control agents of mosquitos was initiated in Malaysia in 1986. A total of 725 samples were collected and 2,394 bacterial colonies were isolated and screened for larvicidal activity. From such screening, 20 Bacillus thuringiensis, 6 B. sphaericus, 1 Clostridium bifermentans and 2 Pseudomonas pseudomallei larvicidal isolates were obtained. Of these, a new B. thuringiensis named as subspecies malaysianensis was found, while the C. bifermentans was also a new anaerobe individualized as serovar malaysia. It was concluded that this screening program was highly successful.
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)
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.
A screening program searching for indigenous microbial control agents of mosquitos in Malaysia is initiated since 1987 and to date at least 20 isolates of mosquitocidal Bacillus thuringiensis serotypes have been obtained. Preliminary field evaluation of several isolates indicated that they are highly effective in the control of medically important mosquito species. For operational purposes, there is an urgent need to produce this agent utilizing cheap and locally available wastes through fermentation biotechnology. Fermentation studies in shake-flasks containing standard nutrient broth and soya bean waste, respectively, indicate that it takes about 37 hours for a Malaysian isolate of B. thuringiensis serotype H-14 to mature. In the grated coconut waste, fishmeal and rice bran, the bacteria took 28 hours, 26 hours and 126 hours respectively to mature. The endotoxin was harvested from the standard nutrient broth at 55 hours and at 50 hours from soybean, grated coconut waste and fishmeal. The endotoxin could only be harvested 150 hours after inoculation from rice bran medium. However, no bacterial growth was detected in palm oil effluent. In terms of endotoxin and biomass production, fishmeal appears to be a suitable medium. Variations in the pH of the fermenting media were also noted.
Field trials were conducted in two residential areas of Petaling Jaya Municipality to test the adulticidal and larvicidal effects of malathion 96% TG and Resigen on Aedes aegypti. Malathion is the currently used insecticide in Malaysia for the control of dengue. The Leco HD ULV machine was used throught the trials. For malathion the flow rate was 90 ml/minute at a vehicle speed of 8kph and for Resigen the flow rate was 200 ml/minute at the same vechicle speed. Malathion was more effective giving higher mortality rates when compared with Resigen. The mortality rate of adult Ae. aegypti outdoor was higher than in the living room and kitchen. Both insecticides did not show promising larvicidal effects.
The efficacy of two formulations, wettable powder and emulsifiable concentrate, of cyfluthrin sprayed on plywood [10 mg (ai)/m2] was assessed against six species of mosquitos. The bioassay followed the WHO standard method, with some modification for the bioassay of insecticidal deposits on wall surfaces. The results indicated that these two formulations of cyfluthrin were effective against Anopheles dirus and Mansonia uniformis, moderately toxic to Aedes aegypti and Ae. albopictus in decreasing mortality through out the study period. It was least effective against Culex quinquefasciatus and An. maculatus, respectively. There was no statistically significant difference between these two formulations.
In spite of more than 30 years of control activities, malaria continues to be the most important parasitic infection in Malaysia, accounting for 39,189 confirmed cases in 1991, giving an annual parasite incidence rate of 2.2 per 1,000 population. Some factors contributing to the continued transmission of malaria are the development of drug resistant Plasmodium falciparum, changes in vector behavior, and ecological changes due to socio-economic reasons. Malaria parasite rates are higher among the Aborigines, land scheme settlers and those in intimate contact with the jungle, like loggers. There has been no substantial change in the proportion of the three common malaria species responsible for infections, P. falciparum, P. vivax, P. malariae and mixed infections accounting for about 70%, 28%, 1% and 1%, respectively of all infections. Drug resistant P. falciparum is unevenly distributed in Malaysia, but based on clinical experience and in vitro drug sensitivity studies, chloroquine resistance is frequently encountered. There has been clinical and laboratory evidence of resistance to sulfadoxine/pyrimethamine combination as well as quinine, but all these have so far been successfully treated with a combination of quinine and tetracycline. The eradication of the disease is impossible in the near future but there is confidence that with better surveillance techniques and the use of alternative control measures like permethrin impregnated bed-nets to complement existing ones, the target of bringing down the annual parasite incidence to 2 per 1,000 population during the Sixth Malaysian Plan period (1991-1995) can be achieved.
Insecticide-impregnated bed nets act as a physical barrier to repel and kill mosquitos. Community intervention trials suggest that these nets are effective in preventing malaria-related mortality and morbidity--but not malaria infection--in areas of low and moderate transmission; the results from areas of high transmission are not so encouraging. Comparison of the results from these trials and their interpretation are difficult because of variations in the epidemiology of malaria and several methodological flaws. Problems such as defining appropriate health indicators, monitoring bed-net usage, introducing bed nets randomly, selecting adequate controls, performing statistical analysis, and comparing bed nets with other available interventions are considered. Further community intervention trials are needed, paying attention to the methods and to assessment of their impact on malaria.
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 residual effectiveness of 0.005mg/ml of cyhalothrin applied to cattle was determined against three species of mosquitos: Anopheles maculatus Theobald. Anopheles dirus Peyton and Harrison Mansonia uniformis Theobald. Twenty-four hour post exposure mortality and the degree of successful blood engorgement were determined by exposing mosquitos for 10 minutes to cattle. Three replicated assays were conducted and mortality determined at 1, 2, 7, 14 and 21 days after each treatment. An initial mortality of 92-94% for An. dirus and Ma. uniformis and 79% for An. maculatus was obtained. Percentage mortality declined to 10%, 18% and 31% for An. maculatus, An. dirus and Ma. uniformis respectively on day 7 post application. On day 21 post application, percentage mortality was 2-3% for the three species of mosquitos.
A novel method for the control of Mansonia larvae was developed and tested. In this method, foliar absorption and translocation of a chemical insecticide, monocrotophos, a known systemic insecticide was studied in the Eicchornia plant. Acetone solution of the insecticide was painted onto leaves of the plant. At daily intervals, stems were severed and divided into equal sections which were introduced into bowls. Larvae of Aedes aegypti were tested for the presence of monocrotophos. It was found that translocation of the insecticide occurred at different rates in the stems and in some plants the chemical was also released into the surrounding water. Based on these results, 2 insecticides namely, monocrotophos and temephos were painted onto leaves of the host plant and their translocation to the root and water environment was examined by testing with Mansonia and Aedes aegypti larvae. The results again confirmed the translocation process and it was found that the insecticides were secreted into the surrounding water, thereby killing the larvae. However, in leaves painted with permethrin (synthetic pyrethroid) or flufenoxuron (chitin synthesis inhibitor), such a process was not detected. The potential of this new concept in Mansonia larval control is examined.
Two field trials in the control of subperiodic brugian filariasis vectors, mainly Mansonia bonneae and Mansonia dives were carried out in Sarawak, East Malaysia. In the first trial, malathion ultra-low volume (ULV) spray was used to control the Mansonia mosquitos in two filariasis endemic villages. Six spray rounds were applied at biweekly intervals at Kampung Rasau and two spray rounds were applied at monthly intervals in Kampung Triboh. ULV malathion spray reduced biting Ma. bonneae population for 3 days after spraying. The biting density decreased to 50% of the pre-treatment level by the 12th - 13th day and reached the pre-treatment level by the 24th - 25th day. Contact bioassay tests on caged Mansonia mosquitos revealed considerable penetration of the malathion aerosol indoors and relatively adequate coverage outdoors. The estimated number of bites per case per day was 1.09 to 4 times less in the sprayed kampung than in an unsprayed control kampung. The parous and daily survival rates of Mansonia mosquitos were not significantly affected by the spraying. In a second trial, chemotherapy with diethylcarbamazine citrate (DEC) was combined with vector control through indoor residual spraying in Kampung Ampungan. The results were compared with the use of only DEC mass treatment in Kampung Sebangkoi and Kampung Sebamban. The combined control measures in Kampung Ampungan reduced the MfD-50 to 44% of the pre-treatment level over a period of 4 years. In the other two kampungs where only mass DEC therapy was applied, the microfilarial rate and MfD-50 declined significantly in the second blood survey but increased gradually in two subsequent follow-up blood surveys. The total insecticidal impact for Ma. bonneae was 3.9 to 1 indoors and 2.7 to 1 outdoors. These results indicated that quarterly pirimiphos-methyl indoor spraying used in integrated control could reduce indoor transmission by 3.9 times. The infective rate from the Ma. bonneae dissected in all three kampungs after the interventions, irrespective of DEC treatment alone or in combination with pirimiphos-methyl residual spraying were reduced by two fold. However the infection rate of brugian filarial larvae in Kampung Ampungan was significantly reduced after the use of DEC and insecticide. Annual Transmission Potential (ATP) showed a high significant reduction in Kampung Ampungan (p > 0.001) compared with Kampungs Sebangkoi and Schambam. In Ampungan, the ATP was reduced by 8.5 times indoors after the MDA and insecticidal application and 3 times outdoors. The reduction rate for Sebangkoi and Sebamban both indoors and outdoors were less than 2 fold.(ABSTRACT TRUNCATED AT 400 WORDS)
The genus Mansonia is divided into two subgenera, Mansonia and Mansonioides. The subgenus Mansonioides includes the important vectors of lymphatic filariasis caused by Brugia malayi in South and Southeast Asia. Six species of this subgenus are vectors of two types of brugian filariasis, periodic and subperiodic. All six species, viz Mansonia bonneae, Ma. dives, Ma. uniformis, Ma. annulifera, Ma. annulata and Ma. indiana are present in this country. The ecological factors governing the larval and adult biology and their control measures are discussed.
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 effect of permethrin impregnated bednets on Anopheles maculatus Theobald was studied in four villages in Pos Betau, Pahang, Malaysia from August 1990 to July 1992. Collections of mosquitos were carried out indoors and outdoors from 1900 to 0700 hours. All mosquitos were dissected for sporozoites and parity. In May 1991 two villages received bednets impregnated with permethrin at 0.5 g/m2 and two villages received placebo bednets. There was a significant difference in the sporozoite and parous rates between the treated and control villages after the distribution of bednets (p < 0.05). There was no significant difference in the bites/man/night of An. maculatus between the pre and post treatment periods in the control villages. However there was a significant difference in bites/man/night between pre and post treatment in the treated villages (p < 0.001).
Thirteen strains among 3 species of entomopathogenic bacteria were tested against 3 medically important mosquito species in French Polynesia. Two strains of Bacillus thuringiensis were highly toxic to Aedes polynesiensis, Aedes aegypti, and Culex quinquefasciatus. Six of 7 strains of Bacillus sphaericus tested were highly toxic to Cx. quinquefasciatus but not to the Aedes spp. Clostridium bifermentans serovar. malaysia was more toxic to Ae. polynesiensis than to the other 2 species. Entomopathogenic bacteria merit field testing for larval mosquito control in French Polynesia.
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.