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Pilot experiments in the control of bancroftian filariasis in Japan and Ryukyu.

In this paper the author reviews the literature on the distribution and epidemiology of filariasis in Japan and discusses the extensive programme of research on the disease that is at present being carried out there. As part of this programme, comparative pilot experiments were started in 1958, in several areas of differing filariasis endemicity, with the object of determining the most effective and economical methods for preventing and treating the disease. The results so far obtained from these pilot experiments, which are still in progress, suggest that a close approach to the eradication of filariasis from the endemic areas could be reached through the administration of diethylcarbamazine at a suitable dosage to microfilaria carriers and the simultaneous application of control measures against the vector mosquitos.

Animals↗

[Control of malaria using mosquito nets impregnated with pyrethroids in Burkina Faso].

An experimental trial of malaria control was carried out in the village of Karangasso in the south-west Burkina Faso. It was based on the use by the whole population of deltamethrin impregnated bed nets at 25 mg/m2. During the first year pretreatment data on entomology, parasitology and pathological incidence of malaria were collected in the whole village. During the second year a quarter of the village with a population of 1,200 was chosen for the experiment and impregnated bed nets were given to everybody while the other quarter of the same population size was kept as a control area. Malaria transmission was reduced by 82% due to the decrease of both vector populations and sporozoitic indexes. It should be pointed out that this reduction in transmission was evaluated on non-protected catchers and consequently was underestimated for the villagers sleeping under nets. Parasitic index remained about the same but the mean parasitic load decreased significantly. Pathological incidence, based on the number of clinical malaria cases confirmed by blood examination, decreased by 59%. This trial shows that mass use of deltamethrin impregnated bed nets should be considered as a valuable tool for malaria control. The purchase of bed net is expensive but could be reduced sharply. The cost of the impregnation is very low regarding the residual effect which remains one year. The acceptance by the population was good.

Animals↗

Apparent influence of the stage of blood meal digestion on the efficacy of ground applied ULV aerosols for the control of urban Culex mosquitoes. I. Field evidence.

The impact of ULV resmethrin on urban Culex mosquitoes was evaluated in 4 field trials by monitoring daily oviposition rate. A well-defined oscillation of effect, with a period corresponding to the duration of the gonotrophic cycle, was observed. We postulate that this oscillation arises from changes in susceptibility following blood feeding and/or behavioral factors. The data indicate that a single treatment with ULV may be inadequate for the effective control of vector mosquitoes.

Aerosols↗

Spatial occurrence and hatch of field eggs of the tadpole shrimp Triops newberryi (Notostraca: Triopsidae), a potential biological control agent of immature mosquitoes.

The tadpole shrimp (TPS), Triops newberryi (Packard) (Notostraca: Triopsidae) is a potential biological control agent for immature mosquitoes breeding in ephemeral habitats. The occurrence of TPS eggs in soil and their hatch were investigated in 11 flood-irrigated date gardens in the Coachella Valley of southern California in 1999. Each garden was sampled several times after the rows were recently irrigated. All these date gardens harbored from very few to a large number of eggs in the soil. Overall, the average density of total eggs on ranches with clay loam soil was significantly higher than that on ranches with silt loam soil. The average densities of total eggs were significantly lower on the ranches that were disked compared to those on the ranches that were undisked before sampling. Two types of eggs were found and designated as "fresh" (yellowish to brownish) and "old" (blackish) eggs. This is the first time that these dimorphic eggs have been reported. The density of fresh eggs was lower than that of old eggs in most soil samples. The date gardens with high egg densities were sampled for determination of vertical occurrence, where soil was sampled up to 38.5 cm deep. Fresh eggs were recovered from soil in depths up to 25.6 cm, but the densities progressively declined with depth. The old eggs, however, were recovered from all soil depths studied, and there was no obvious relationship between soil depth and their density. This pattern of vertical occurrence of TPS eggs is the result of frequent disking for weed control and fruit harvest. Hatch of TPS eggs in surface soil samples ranged from 0 to 7.2 per 100 g dried soil. Hatch of viable eggs had an inverse relationship with soil depth. No TPS hatched out from the soil samples taken deeper than 15.4 cm. Fresh and old eggs distinguished by color were subjected to hatching tests. Fresh eggs exhibited high hatch, with hatching rates of 35.5-45.0% and 40.2-60.3% for the 1st and 1st plus the 2nd hydrations respectively. The old eggs, however, did not hatch at all. These findings provide quantitative information with regard to occurrence of natural TPS populations in flood irrigated agricultural fields, which could serve as a potential regulatory force of immature mosquito populations sharing ephemeral habitats with TPS.

Animals↗

Telephonic survey of surveillance and control procedures for the mosquito vectors of West Nile virus near naval installations in the eastern United States.

Surveillance and control procedures for the mosquito vectors of West Nile virus (WNV) and other arboviruses are described in response plans that vary among states. To ensure that naval installations in the eastern United States follow WNV response plan criteria similar to those of their host states, we conducted a telephone survey of 25 personnel who directed surveillance and control procedures in areas near these installations. For adult mosquito surveillance, 76% of respondents used Centers for Disease Control and Prevention miniature light traps baited with dry ice; 68% of respondents used these and baited Centers for Disease Control and Prevention gravid traps. We report a summary of the mosquito species that were most problematic among states. In the eastern United States, these species have tested positive for WNV and some have been reported as potential vectors of WNV and other arboviruses. Among respondents, numerical thresholds or the presence of WNV-positive mosquito pools facilitated decision-making (i.e., whether to increase surveillance or to initiate control procedures). The presence of mosquito larvae, abiotic variables, and historical databases were also important. Reports of dead birds and human serology data were used by 92% and 64% of respondents, respectively. Adult control was accomplished with synthetic pyrethroids; larvae were controlled with microbial insecticides and growth regulators. Geographic information systems and public awareness/education were used by 60% and 88% of respondents, respectively. We discuss our results in light of response plan variability and implications for the future.

Animals↗

The control of anopheline mosquitos by the spraying of Deltamethrin on raffia curtains used in miners' huts in areas endemic for malaria.

The residual potential of an aqueous solution of Deltamethrin (FW 25 mg i.a./m) was evaluated on raffia curtains. These are sheets of synthetic material used in the construction of huts to house miners. Experiments were conducted during 420 days and the curtains were always rolled up in the daytime and unrolled in late afternoon. Data analyzed by logarithmic regression indicated that raffia treated with Deltamethrin had higher mortality indices than that covered with DDT. The residual capacity of Deltamethrin on raffia was high. The mortality percentage was above 85% after 360 days and dropped to about 50% at 420 days. The effect of DDT was reduced after 180 days and reached zero by the end of the experiment. Based or the results of these experiments, it is recommended that Deltamethrin be used to spray raffia curtains in mining regions and other areas that are endemic for malaria.

Animals↗

Optimal conditions for rearing the tadpole shrimp, Triops longicaudatus (Notostraca:Triopsidae), a biological control agent against mosquitoes.

Tadpole shrimp (TPS) were reared at 15, 20, 25, and 30 degrees C in the laboratory. Size of TPS was temperature and age dependent with more rapid development at warmer temperatures. Survivorship was inversely related to rearing temperature. Mean age at death was 24.2, 19.2, 14.3, and 11.8 days at 15, 20, 25, and 30 degrees C, respectively. Rearing temperature (excluding 15 degrees C) did not affect lifetime fecundity, but larger TPS laid more eggs than smaller ones. Tadpole shrimp began ovipositing earlier at higher temperatures, and at a smaller size than their counterparts in lower temperatures. Mean age at reproductive maturity was 18.8, 13.1, and 10.2 days and mean carapace length was 10.8, 11.0, and 10.3 at 20, 25, and 30 degrees C, respectively. Embryogenesis required a minimum of 3 days for completion. Hatching rates during the first hydration decreased with increasing egg batch number produced by individuals, ranging from a mean of 74% for the first batch to 31% for the 5th batch. Cumulative hatching rates of eggs after 2 hydrations were consistent across temperatures and egg batches (79 +/- 2%).

Animals↗

Phenotypic and genetic diversity among Bacillus sphaericus strains isolated in Brazil, potentially useful as biological control agents against mosquito larvae.

Thirty mosquitocidal strains of Bacillus sphaericus isolated from different sources and localities in Brazil were characterized phenotypically and genetically to determine their relationship. Among the strains tested, 93.3% were shown to be resistant to lincomycin, 96.6% to novobiocin, 60% to chloramphenicol and all strains were resistant to streptomycin. Resistance to HgCl2, NiSO4.6H2O and CuSO4 was observed in 83.3, 86.6 and 100% of the strains, respectively. All strains were inhibited by the presence of CoSO4. Tolerance to ethanol and variable responses to different amounts of creolin, phenol and xylol was also observed. Amplification of DNA of each of 30 isolates using repetitive primers allowed the identification of 5 groups of similar strains in BOX-PCR and 8 groups in REP-PCR. Using cloned toxin genes from B. sphaericus as probes in hybridization studies, 83% of the strains studied hybridized to the bin probe and 90% to the mtx probe. A comparison of the 30 strains by similarity matrix analysis using the data obtained in all approaches used in this study resulted in 22 groups (16 groups among the 24 high-toxicity strains) at 100% similarity, indicating a high degree of diversity among the strains tested. Some of the strains studied here, which are resistant to different stress conditions, should be considered for further ecological studies.

Animals↗

Control of acidic drain-water-breeding mosquitoes in New South Wales, Australia, by installing controlled leakage holes in tidal flap gates.

Effects on mosquito breeding, acidity, and fish presence were assessed after installation of a small tidal leakage port into an acidic drain's tidal exclusion flap gate. Before gate modification the drain water had pH values as low as 2.7. These water conditions were toxic to fish and continually held mosquito larvae. At 4 wk after gate modification, water pH had risen to 6.0, at least 3 fish species inhabited the drain, and mosquito larval numbers had been reduced by 99.98%.

Animals↗

Laboratory and field comparisons of pyriproxyfen, polystyrene beads and other larvicidal methods against malaria vectors in Sri Lanka.

Hand-dug gem pits are important breeding sites for larvae of malaria vectors in Sri Lanka. Therefore, studies were carried out to help to select an effective, economic and convenient method that could be used to control malaria vector mosquito breeding in gem pits in a mining area. The effectiveness of four types of floating layers of polystyrene was compared in the laboratory and it was found that 2 mm expanded beads were the most effective for suffocating Anopheles larvae and pupae. The insect growth regulator, pyriproxyfen at dosages of 0.01 and 0.1 mg/l were tested in the laboratory and complete inhibition of emergence was found at both concentrations. A small-scale field trial was carried out for over a year to assess the efficacy of two concentrations of pyriproxyfen, 2 mm diameter expanded polystyrene beads, temephos, used engine oil and filling pits with soil. Pyriproxyfen only required re-application twice a year, whereas temephos or oil require 12 applications per year. Due to re-excavation by gem miners, polystyrene beads and filling of pits were not as permanent solutions as was expected. Calculations based on all available data showed that two annual treatments with pyriproxyfen at 0.01 mg/l would be the most cost-effective method with oil only slightly more expensive. However, the reduced required frequency for visiting every pit made the pyriproxyfen method the one of choice. The same low concentration of pyriproxyfen also effectively inhibited emergence of adults from river-bed pools.

Animals↗