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Effect of intermittent irrigation on mosquitoes (Diptera: Culicidae) and larvivorous predators in rice fields.

Effect of intermittent irrigation to facilitate rice production on rice-field mosquitoes and larvivorous predators was studied in Saga, Japan. Mosquitoes and associated taxa were sampled by dipping in two rice fields subject to intermittent irrigation and in one rice field that remained flooded throughout the study period of approximately 1 mo. With the onset of intermittent irrigation, larval mosquito (Culex tritaeniorhynchus Giles and Anopheles sinensis Wiedemann) abundance decreased; reirrigated fields were colonized initially by first instars. Abundance of aquatic arthropod predators and larvivorous fish also decreased drastically. Water from irrigation canals was considered to be a major source of recolonization by these predators with limited breeding seasons and longer developmental periods than mosquitoes. Richness (number of taxa) of aquatic insect communities decreased, but the percentage mosquitoes among insects increased with repeated intermittent irrigation. Manipulation of rice fields and associated canals as a whole is essential to rice-field mosquito control by water management.

Agriculture↗

Isolation of indigenous larvicidal microbial control agents of mosquitos: the Malaysian experience.

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.

Animals↗

Community-based rice ecosystem management for suppressing vector anophelines in Sri Lanka.

Sri Lanka is one of the Asian countries most affected by mosquito-borne diseases, especially malaria. This 18-month study assessed the effectiveness of a new community-based ecosystem management programme to control mosquito vectors in the country's rice ecosystem. Farmers in a malaria-prone village were educated and motivated to engage in source reduction as well as measures to restore and maximise rice ecosystem functions. Over the course of the programme, the impact of farmers' ecosystem management on local mosquito ecology was also examined. Although little impact was detected on Culex and Aedes densities, adult Anopheles density was significantly suppressed in the southwest monsoon season. Rice farmers who manage their ecosystems can reduce the burden of Anopheles mosquitoes, interrupt malaria transmission and prevent the destruction of ecosystems.

Adolescent↗

Carbamate-resistance in mosquitos. Selection of Culex pipiens fatigans Wiedemann (=C. quinquefasciatus Say) for resistance to Baygon.

The authors investigated the rate of development and other characteristics of Baygon-resistance in Culex pipiens fatigans (=C. quinquefasciatus) recently colonized from Southern California. Selective pressure against the larvae (strain L) for 35 generations resulted in 25.4-fold resistance in larvae, but only 3-fold and 4.8-fold resistance in adults, as determined by contact and topical application, respectively. Conversely, selective pressure on adults (strain A) for 24 generations resulted in 8.4-fold (contact) and 5.3-fold (topical) resistance in adults, but only 2.7-fold resistance in larvae. About 10% of strain A adults survived 1-hour contact exposure even when the concentration of Baygon was increased 100-fold. This was not due to enhanced phototropism in this stage. Larvae of strain L metabolized (14)C-labelled Baygon at a rate 2.5-fold greater than the non-selected strain. Cross-resistance in strain L to carbamates closely related to Baygon was high, but was extremely low to remotely related carbamates.The authors consider the relatively slow rate of development of resistance to Baygon, the reduced expressivity of the resistance character in adults, and its specificity for the selective agent and for closely related carbamates to be encouraging indications as to the usefulness of this class of compounds for mosquito control.

Carbamates↗

Field efficacy and nontarget effects of the mosquito larvicides temephos, methoprene, and Bacillus thuringiensis var. israelensis in Florida mangrove swamps.

We compared the efficacy and nontarget effects of temephos, Bacillus thuringiensis var. israelensis (B.t.i.), and methoprene applied by helicopter to control mosquito larvae in mangrove swamps on Sanibel Island, FL, in May 1997. Three sites per treatment and 3 untreated sites were used. Temephos (Abate) was applied at 37 ml/ha (43% active ingredient [AI]), B.t.i. granules (Vectobac G) were applied at 5.606 kg/ha (200 International Toxic Units/mg), and methoprene (Altosid ALL) was applied at 213 ml/ha (5% AI). Efficacy was quantified by monitoring the survival of caged and uncaged larval Aedes taeniorhynchus. We quantified mortality of sentinel nontarget amphipods (Talitridae) at all sites, monitored the effect of temephos on flying arthropods using light traps, and collected dead insects in tarps suspended under mangroves in areas treated with either temephos or methoprene. Each pesticide showed good overall efficacy but occasional failures occurred. No detectable mortality of amphipods or flying insects attributable to pesticides was found. The inconsistent field efficacies of the pesticides indicate a need for reinspection of treated sites in this habitat.

Aedes↗

Using GIS and historical records to reconstruct residential exposure to large-scale pesticide application.

Investigation of pesticide impacts on human health depends on good measures of exposure. Historical exposure data are needed to study health outcomes, such as cancer, that involve long latency periods, and other outcomes that are a function of the timing of exposure. Environmental or biological samples collected at the time of epidemiologic study may not represent historical exposure levels. To study the relationship between residential exposure to pesticides and breast cancer on Cape Cod, Massachusetts, historical records of pesticide use were integrated into a geographic information system (GIS) to estimate exposures from large-scale pesticide applications between 1948 and 1995. Information on pesticide use for gypsy moth and other tree/vegetative pest control, cranberry bog cultivation, other agriculture, mosquito control, recreational turf management, and rights-of-way maintenance is included in the database. Residents living within or near pesticide use areas may be exposed through inhalation due to drift and volatilization and through dermal contact and ingestion at the time of application or in later years from pesticides that deposit on soil, accumulate in crops, or migrate to groundwater. Procedures were developed to use the GIS to estimate the relative intensity of past exposures at each study subject's Cape Cod addresses over the past 40 years, taking into account local meteorological data, distance and direction from a residence to a pesticide use source area, size of the source area, application by ground-based or aerial methods, and persistent or nonpersistent character of the pesticide applied. The resulting individual-level estimates of relative exposure intensity can be used in conjunction with interview data to obtain more complete exposure assessment in an epidemiologic study. While the database can improve environmental epidemiological studies involving pesticides, it simultaneously illustrates important data gaps that cannot be filled. Studies such as this one have the potential to identify preventable causes of disease and guide public policies.

Agrochemicals↗

Novel fermentation media for production of Bacillus thuringiensis subsp. israelensis.

The production of Bacillus thuringiensis subsp. israelensis (deBarjac) (Bti) as a biopesticide is not cost-effective using existing fermentation technology. In this study, we explored the use of several less expensive alternative culture media (potato, common sugar, and Bengal gram) for the growth and production of Bti. Growth was obtained in all tested media and was comparable to that obtained in conventional medium (Luria-Bertani). Toxicity assays showed that the toxin produced from the novel growth media were effective in killing larvae of Culex quinquefasciatus, Anopheles stephensi, and Aedes aegypti and toxicity was comparable to that produced from Luria-Bertani medium. These observations suggest that potato can be used as a cheap source of culture medium for the production of Bti toxin in mosquito control programs.

Aedes↗

[Biological control of vectors of human and tropical diseases. Present means and prospects (author's transl)].

Biological control is "direct or indirect use of natural enemies of the injurious species to increase its mortality" (W.H.O., 1963). The more and more frequent apparition of resistant insects populations, the fears as regards the environment, the increase cost of hydrocarbur products and also some technic and operational difficulties to stop transmission by the use of only insecticide pulvérisation, impose this process. Nevertheless, practic use of natural enemies of vectors is yet unusual in spite of important research. (Identification problems, dynamic of species, insufficiency of ethology knowledge particulary of the host specificity, difficulties of application on the vectors which are the most usually widely scattered). For control of insects of medical importance (mosquitoes, black flies, tse-tse flies) it has been used either pathogen agents such as virus bacteria, microsporida or parasit agents such as fungi, mermithid nematods or at last, predators, essentially larvivorus fish. Actually, no biological agent is able to take the place of chemical and physical "traditional" means. In case of mosquito control which is more advanced, the only biological mean which is operational is the use of larvivorus fish and specially Gambusia.

Africa↗

West Nile virus in the United States: an update on an emerging infectious disease.

West Nile virus is a mosquito-borne flavivirus and human neuropathogen. Since the virus was recognized in New York City in 1999, it has spread rapidly across the United States, with human disease documented in 39 states and the District of Columbia. West Nile virus can cause a broad range of clinical syndromes, including fever, meningitis, encephalitis, and a flaccid paralysis characteristic of a poliomyelitis-like syndrome. Approximately one in 150 infections results in severe neurologic illness. Advanced age is the greatest risk factor for severe neurologic disease, long-term sequelae, and death. Physicians should consider West Nile virus infection when evaluating febrile patients who have unexplained neurologic symptoms, muscle weakness, or erythematous rash during late spring through early fall, or throughout the year in warm climates. West Nile virus infection has no characteristic findings on routine laboratory tests, although anemia, leukocytosis, or lymphopenia may be present. Testing for IgM antibody to West Nile virus in serum or cerebrospinal fluid (samples from the acute and convalescent phases, submitted at least two weeks apart) is the most common diagnostic method. Local or state health departments usually can perform the test within 24 to 36 hours of submission. Treatment is supportive. Prevention relies on comprehensive mosquito-control programs and measures to avoid mosquito bites, including the use of mosquito repellents containing N,N-diethyl-m-toluamide.

Animals↗

[The recycling of waste water and mosquitoes].

Recycling waste water in the Achères complex (North-West Paris) is based on both sophisticated industrial techniques and simple agricultural methods. The sewage farms and settling pools provide suitable breeding sites for more than ten mosquito species. Aedes caspius is the major pest for the local population. Moreover Culex pipiens (anthropophilic form) breeds in the sewers of the neighbouring towns. Mosquito control is based early ground treatment of breeding sites. Temephos and fenotrothion are used against A. caspius. Spherimos (Bacillus sphaericus) is used to control C. pipiens. The two insecticides have no adverse effect on humans or the environment and Spherimos is harmless. Aedes pest have been virtually eliminated. Urban Culex control is generally good despite being performed by less well trained municipal employees. In the areas treated by the specialized team of the SIAAP, pest mosquitoes have disappeared. The techniques used in the Achères complex do not require sophisticated equipment. Thus, if adapted to local ecological, epidemiological and financial conditions they could be transferred to developing countries.

Aedes↗

Effects of suspended residual spraying and of imported malaria on malaria control in the USA.

The activities of the National Malaria Eradication Programme, a co-operative campaign inaugurated in July 1947 by the United States Public Health Service and certain State and local health agencies, are outlined. Control operations reached their maximal level in 1948, when 1,364,950 dwellings in 13 "malarious" States were sprayed with residual DDT, and the percentage of mosquito control achieved was 83.2.In 1950, only 2,227 cases of malaria were reported, as compared with 16,203 in 1947 and 9,797 in 1948. But the return of infected servicemen from Korea caused a temporary increase in the incidence in 1951 and 1952, when the totals were 5,600 and 7,023, respectively. In 1953, however, only 559 civilian cases were reported; of the cases appraised, 28 were of local origin, and, of these, at least 24 are known to have been infected in 1952.The Public Health Service ceased active participation in the Programme in 1951, but continued to give technical advice. At the same time, State authorities received Federal support in activating malaria surveillance-and-prevention programmes. More-selective anti-anopheline activities have replaced residual insecticide spraying, which is now carried out in only a few isolated areas. It is believed that these measures have prevented imported malaria from increasing the diminishing incidence of primary indigenous cases in the USA.

Biomedical Research↗

Activity of lambda-cyhalothrin applied as an ultralow volume ground treatment against Anopheles quadrimaculatus adults.

Lambda-cyhalothrin was evaluated as an ultralow volume ground adulticide treatment at rates of 0.25, 0.5 and 1.0 g/ha. Resmethrin, a standard adulticide, was applied at a rate of 1.96 g/ha. All treatments provided greater than or equal to 95% control up to 50 m from the spray route. The highest rate of lambda-cyhalothrin and the resmethrin standard provided greater than or equal to 95% control up to 200 m, which is twice the distance normally assessed in this type of testing. Control was reduced at 200 m for the 0.25 and 0.5 g/ha rates of lambda-cyhalothrin, which provided 73 and 88% mortality, respectively. Lambda-cyhalothrin appears to have the insecticidal activity required for operational mosquito control.

Animals↗

Aerial ultra-low-volume assessment of ANVIL 10+10 against Anopheles quadrimaculatus.

Against caged field-collected adults of Anopheles quadrimaculatus, optimized aerial applications of ANVIL 10+10 at 18.4 ml (1.63 g active ingredient)/0.4 ha produced a mean mortality of 92% at 1, 12, and 24 h after treatment. These trials were conducted with 7 stacked passes applied 1,067 m upwind of the target site when wind velocity was 18-21 km/h at an application altitude of 46 m and 5-10 km/h at groundlevel. When the wind velocity aloft was greater than might be operationally acceptable (27 km/h), reduced efficacy (64% mortality) was observed in the bioassay site (1,524 m downwind from 11 stacked passes) in an unreplicated application. Droplets from the 2 tail-mounted Beecomist 360-A-12-V rotary atomizers (fitted with wire sleeve cages of size 40 mesh) collected on spinning Teflon-coated slides in the target area averaged a volume mean diameter (VMD) of 29 microm and a droplet density of 39 droplets/cm2 in 18- to 21-km/h winds. With 27-km/h winds aloft and a greater application offset, the VMD and droplet density dropped to 23 microm and 18 droplets/cm2, respectively. Coupled with unreplicated results from a nonoptimized application, these tests provide further documentation of the efficacy of ANVIL 10+10 for wide-area adult mosquito control and for optimization technology.

Aircraft↗

The perspective of Aedes albopictus from the administrative viewpoint.

Mosquito control administrators should consider a newly introduced species in view of local conditions. Aedes albopictus was discovered in Harris County while surveying for Aedes aegypti. Recognizing a potential threat to public health, local and state officials were notified of the discovery. Questions posed by the introduction of a foreign species requires a cooperative application of research resources. The Centers for Disease Control (CDC) should serve as the coordinator of this effort.

Aedes↗

[Evidence of very high resistance to chlorpyrifos and permethrin in Culex pipiens populations in Tunisia].

Resistance to two organophosphorous insecticides (temephos and chlorpyrifos) and one pyrethrinoid (permethrin) was studied in larvae of five Culex pipiens samples collected in Gafsa, Telalsa, Sayada, Monastir et Sfax. Large variations in the tolerance to these insecticides was observed between samples. Gafsa sample was the most susceptible and disclosed little difference when compared to the susceptible reference strain. In contrast, at LD95 the resistance ratio (RR) was 8 folds with temephos, 9000 folds with chlorpyrifos, and 1500 folds with permethrin in the Sfax sample. These results are discussed in relation to resistance mechanisms and mosquito control.

Animals↗

Oviposition habitat selection in response to risk of predation in temporary pools: mode of detection and consistency across experimental venue.

Natural selection should favor females that avoid ovipositing where risk of predation is high for their progeny. Despite the large consequences of such oviposition behavior for individual fitness, population dynamics, and community structure, relatively few studies have tested for this behavior. Moreover, these studies have rarely assessed the mode of detection of predators, compared responses in prey species that vary in vulnerability to predators, or tested for the behavior in natural habitats. In an outdoor artificial pool experiment, we tested the oviposition responses of two dipteran species, Culiseta longiareolata (mosquito) and Chironomus riparius (midge), to the hemipteran predator, Notonecta maculata. Both dipteran species have similar life history characteristics, but Culiseta longiareolata larvae are highly vulnerable to predation by Notonecta, while Chironomus riparius larvae are not. As their vulnerabilities would suggest, Culiseta longiareolata, but not Chironomus riparius, strongly avoided ovipositing in pools containing Notonecta. An experiment in natural rock pools assessing oviposition by Culiseta longiareolata in response to Notonecta maculata yielded an oviposition pattern highly consistent with that of the artificial pool experiment. We also demonstrated that the cue for oviposition avoidance by Culiseta longiareolata was a predator-released chemical: Notonecta water (without Notonecta replenishment) repelled oviposition for 8 days. Oviposition avoidance and mode of detection of the predator have important implications for how to assess the true impact of predators and for the use of commercially produced kairomones for mosquito control.

Animals↗

Gambusia affinis: dispersal due to floods and its failure to colonize new water bodies in Shahjahanpur District (U.P.).

In villages of District Shahjahanpur, 122 decentralized Gambusia multiplication ponds were established to cover the need of the entire district. Profuse breeding of Gambusia was observed in these ponds. The fishes are being successfully used in mosquito control all over the district. In July 1990 there was a widespread flood due to which 70 Gambusia multiplication ponds were affected and the fish was washed away in large numbers, leaving only a scanty population in the flood-affected ponds. We utilized this opportunity to study the natural dispersal and colonization of Gambusia in different aquatic habitats. The study revealed that Gambusia was either not found in most habitats or was present in very small numbers, and on its own Gambusia was unable to eliminate the local fauna to become a dominant species. Predatory fishes and birds played a major role in eliminating Gambusia. Gambusia is therefore unlikely to pose any ecological hazard in vector-control programmes.

Animals↗

Local knowledge and treatment of malaria in Agusan del Sur, The Philippines.

Information about local knowledge of malaria, its transmission, treatment and prevention were gathered at the outset of a Malaria Control Program in order to incorporate this information into community interventions. Data were collected using focus groups and indepth interviews with caretakers of children who had had a recent episode of malaria. These were supplemented as baseline data through a survey and the ongoing participation of researchers in the intervention. Local knowledge of malaria was influenced by clinical diagnosis and was based on the coexistence of signs of illness. People conventionally self-medicated or used herbs for symptomatic relief prior to seeking clinical diagnosis and treatment, with treatment delay influenced by the logistic difficulties within the region, direct and indirect costs associated with treatment seeking, and delays in the return of results once a blood film for diagnosis was made. People were familiar with mosquito control activities conducted by the Malaria Control Service and, as a result, most respondents associated malaria with mosquitos. However, the role of the mosquito as the sole vector, and the means by which malaria was transmitted, were not well appreciated.

Adolescent↗