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Onchocerciasis vector breeding along 41 km of the Bussere River in the Wau Area of South-Western Sudan was controlled with temephos (Abate) insecticide for one annual transmission period. Vector biting and transmission was compared to the two years of precontrol data. Up to 70% reductions in vector biting and 80% reductions in transmission were recorded at sites with the highest precontrol levels. The flies invading in the control year (principally those invading from the south-west in the main part of the rainy season) were found to be much less infective - 2390 fly bites would be needed to transmit 100 larvae in the control year, compared to 1490 in the precontrol years. It was concluded that localized vector control could have a major impact on onchocerciasis transmission and that in this, and many other foci in Sudan, permanent reductions could be achieved by causeway removal and selective vegetation clearance.
Following larval insecticide treatment, resistance to the organophosphates temephos and chlorphorxim appeared in a population of the Simulium soubrense/sanctipauli group of the S. damnosum complex on the Bandama Rivers, Ivory Coast. Resistant populations were subsequently identified from other river basins in the north of Ivory Coast. A small chromosomal rearrangement, IIL-A, was found to be associated with resistant populations. Monitoring the presence of this inversion was used to detect the spread or resistance eastwards into untreated areas.
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Larval susceptibility to temephos, malathion and fenitrothion were studied in 6 Aedes, 2 Culex and one Anopheles species from areas with the following agricultural characteristics: VdT, intensively irrigated crops; Zone A, cereals and some irrigation; Zone B, cereals and grasslands; Zone C, oak and pine forests. The susceptibility of adult Anopheles from VdT and Zone B areas to dieldrin and DDT was also studied. The use of insecticides in these areas probably decreases from VdT, to Zone A, to Zone C, to Zone B. Tests of larval and adult susceptibility of mosquitoes in these areas followed the recommendations of WHO re materials and methods. In the absence of any baseline data concerning the susceptibility of the tested mosquito population, the test results only allow one to suspect changes in susceptibility to temephos, malathion and fenitrothion in larvae of An. atroparvus and Cx. theileri from VdT and resistance in adults of An. atroparvus to dieldrin and DDT.
The impact of mosquito control on nontarget organisms using Abate-4-E was investigated in terms of immediate mortality and residual activity. Three 10 year old, man-made ponds having similar community structures and population densities were studied. The residual activity, determined by bioassays with 4th instar Aedes communis, was significantly longer in a relatively cooler pond. Populations of copepods and Cladocera took longer to return to control densities in that same pond. The role played by the physicochemical characteristics of the pond water as well as the intrinsic susceptibility and recovery capacity of the populations considered are discussed.
The relative effectiveness of 4 organophosphate compounds was tested in the laboratory against Culicoides spp. larvae obtained from salt marsh areas on the Gulf coast of Florida. Larvae were exposed to the insecticide either in estuarine water or in a combination of estuarine water and dried substrate from the salt marsh habitat. The relative potency of the 4 chemicals varied greatly, with chlorpyrifos being the most toxic. Nine times as much temephos, 22 times as much fenthion, and 176 times as much malathion were required to achieve the 50% mortality level compared to chloryprifos (LC50, 0.5 ppb) in water. Addition of habitat soil did not change the order of effectiveness, but 9 times as much chlorpyrifos, 2.3 times as much temephos, and 1.3 times as much fenthion or malathion were required to cause the same mortality as in estuarine water alone.
Formulations of temephos (Abate) and Bacillus thuringiensis var. israelensis (B.t.i.) on corncob and dried coconut husk carriers were tested for slow-release insecticide properties against Aedes aegypti larvae in Puerto Rico. Granular formulations of 5% and 10% temephos gave continuous larval control in used automobile tires for 27 to 124 days and 34 to 162 days, respectively. Temephos on radial sections of corncob and coconut husk chips gave good larval control in tires for 27 to 63 and 61 to 134 days, respectively, depending on the size of the carrier. Small (2-3 g) and large (3-5 g) coconut husk chips tested in 167 liter drums provided continuous control for 55 to 105 days, respectively. Granular formulations of B.t.i. controlled Ae. aegypti in tires for 19 to 33 days, and B.t.i. briquets exhibited larvicidal activity in large containers for 26 to 78 days.
During 1984, larval susceptibility tests of temephos were performed on Aedes taeniorhynchus and Culex nigripalpus collected from the same general areas as in 1980-82, and the results compared to the susceptible laboratory strains. No resistance was detected against these two species. When strains of Culex quinquefasciatus from some new areas were tested against temephos, malathion, naled, fenthion and chlorpyrifos, their tolerance varied according to the insecticide tested and the origin of the strain. Some strains ranged from 1.6 to 43.0X more tolerant to temephos when compared to the West Florida Arthropod Research Laboratory strain (WFARL strain).
In laboratory tests, cypermethrin was highly toxic to mosquito larvae and pupae. It was more toxic at low temperatures after a 24 hr exposure. Larvae of Aedes stimulans were less susceptible than Culex restuans. Technical cypermethrin was more toxic than an emulsifiable concentrate formulation. In outdoor simulated pools cypermethrin 40% EC was consistently effective against larvae and pupae of Ae. stimulans at 10 g AI/ha and Culex spp. at 50 g AI/ha. When stickleback fish were tested, no mortality occurred at the lowest effective dosage in each trial. The residual toxicity of cypermethrin increased with dosage and was much higher in a test at 8 degrees C than at 20 degrees C. In natural snowmelt pools, cypermethrin at 20 g AI/ha provided 92-100% control of Aedes spp. larvae and pupae by 7 days after treatment. Non-target amphipod, anostracan, cladoceran and insect populations were usually reduced 80-100% while copepods, ostracods and hydracarinid mites were generally less affected. No significant mortality of caged stickleback fish occurred in these pools.
Temephos, Bacillus thuringiensis var. israelensis (B.t.i.) and methoprene were tested for larval control of Coquillettidia perturbans. Neither temephos nor B.t.i. treatments at their maximum recommended dosages consistently reduced larval numbers. Larval emergencies were reduced 99% in test plots treated with experimental, controlled release methoprene briquets (Altosid SR-10). Breeding sites of Cq. perturbans in a 5,000 km2 area were treated using methoprene briquets in the 1984 season. Adult populations in a 7,700 km2 area were 2.5 times higher in untreated areas than treated areas. Methoprene can effectively control larval populations of Cq. perturbans.
Chemical treatment of step wells to kill cyclopoid vectors of guinea worm by temephos (50 per cent E. C.) at the dose of 1 ppm is now an important activity of the guineaworm eradication programme in India. Calculation of correct volume of water in step wells, to determine the exact quantity of temephos to be applied, therefore, deserves adequate attention to prevent over and underdosing of stepwells by the chemical. The prescribed method of calculation of water volume includes two formulae; pi r2h and 1 x b x h (where h = mean depth for uneven bottoms and is a single depth measurement for almost even bottoms). Field observations revealed that in many stepwells there were marked variations in depth within the same well. These differences in depth ranged from small to very large in some wells. Since these depth variations would lead to miscalculation of water volume by existing method and the dose of temephos to be applied, with eco-epidemiological consequences, new formulae have therefore been deduced for conceivable patterns of depth variations by geometrical and algebric applications. The new formulae will permit calculation of, nearest to, exact quantity of temephos required for application. These formulae have been validated by an example.
The distribution, persistence, and toxicity of the mosquito larvicide temephos was monitored following aerial applications to an intertidal mangrove community in Lee County, Florida. The amount of temephos penetrating to the mangrove floor ranged from 15 to 70% of the amount entering the upper leaf canopy, with 50-60% of that applied remaining on the mangrove leaves. Rainfall caused an additional influx of temephos from the leaves to the mangrove floor. Residues were detected in intertidal water at 2 h, but not 4 h after application. However, temephos was observed to persist in simulated tidal pools and on mangrove leaves for up to 72 h and in oysters for up to 48 h after application. Marine organisms placed in cages at 3 test sites and a control site were monitored for toxic effects. Mortality among natural mosquito larvae was simultaneously monitored. Mysids (Mysidopsis bahia) exhibited a significant mortality at one site during 1 of 3 applications monitored; however, no correlation was observed between mortality and temephos concentration in water. No significant mortality was observed for the other organisms, which included: brown shrimp (Panaeus aztecus), grass shrimp (Palaemonetes pugio), juvenile snook (Centropomis undecimalis) and sheepshead minnow (Cyprinodon variegatus).
Three pesticides were tested in the laboratory (Chlorpirifos, Temephos and Fenthion) against Culex pipiens larvae. The study was conducted in the Area of Tunis during the years 1984 to 1988. After several years of treatment with there organophosphoric compounds, the resistance rates reached by the treated larval population never exceeded 15, which is much lower than the rates observed in other countries.
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