Mosquito population control through the use of chemosterilants.
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In an effort to develop a more effective technique in dispersing a microbial control agent, Bacillus thuringiensis (Bt), a truck-mounted ultra low volume (ULV) generator (Scorpion) was used to disperse B. thuringiensis israelensis (Bti) and Bti with malathion. Complete larval and adult mortalities for all tested mosquito species within the first 70-80 feet from the ULV generator were achieved. Beyond that distance less than 50% mortality was achieved as insufficient sprayed particles reached the area. A minimum of 10(3) Bti colony forming units per ml is required to cause 100% larval mortality. The sprayed Bti larvicidal toxins were persistent in the test water 7 days post ULV. The effectiveness of B. thuringiensis jegathesan (Btj), a new mosquitocidal Bt serotype was also evaluated. Similar mortality results as Bti were achieved except that the Btj toxins underwent degradation in the test water, since less than 50% less in larval mortality was observed in 7 days post ULV samples. This ULV method has the potential to disperse Bt and malathion effectively for a simultaneous control of mosquito adults and larvae.
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The action of bacterial insecticides based on Bacillus thuringiensis H-14 and B. sphaericus in a dose of 0.005-2 mg/l on the mermithids Romanomermis iyengari, R. culicivorax and R. jingdeensis was studied. It was shown that though bacterial agents suppressed mermithid preparasite larvae density about 30-40%, the survivors might invade 100% of mosquito larvae. The viability and fertility of adult mermithids did not change under the influence of bactoculicide in doses 5-50 times higher than those used against mosquitoes in practice. In combined field trials of sphaerolarvicide (1.5 kg/ha) and R. iyengari mermithids the infectivity of Anopheles sacharovi larvae reached 96%. Mermithids in combination with bactoculicide and sphaerolarvicide might be useful in integrated control systems because these bacterial agents are harmless for mermithids of all stages in doses useful against mosquito larvae.
A field trial was conducted in Block F of the Moti Bagh area of New Delhi Municipal Committee to demonstrate composite control of Anopheles stephensi and Aedes aegypti by spraying deltamethrin at 100 mg/m2 on window and door curtains of habitations. Results revealed drastic reduction (87.9-93.7%, P < 0.05) of target species in the experimental area. The impact of deltamethrin-treated curtains was also evident against nontarget species (67.9-85.7%. P < 0.05). Treated curtains provided 100% kill of An. stephensi and Ae. aegypti for 3-4 months, followed by a gradual decline in successive months. Use of deltamethrin-treated curtains resulted in 92.0 reduction in slide positivity rate and 95.4% reduction in malaria cases per thousand population. The cost of deltamethrin treatment was Rs 41.15 (<$1 U.S.) per house per annum. Insecticide-treated mosquito window and door curtains, along with legislative measures, may provide cost-effective concurrent control of mosquitoes and other domestic pests.
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Recently, because of concern about the effects of insecticide on the environment, increased attention is being given to the use of biological agents for controlling the vectors of human disease. Biological control may encompass the use of predators, pathogens, parasites, pheromones, insect growth regulators, and other factors. Of these agents only fish and bacteria have so far been used operationally in mosquito control. Since 1988 fish have been employed for controlling Aedes larvae in water containers in Liuchiu, Pingtung. A review of larvivorous fish (mainly Gambusia affinis) and the present status of the use of fish in mosquito control in Mainland China are thus made for ready reference for the workers in mosquito control in Taiwan.
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A dense plexus of axons, immunoreactive to antisera against 5-hydroxytryptamine (5-HT, serotonin) and surrounding the proximal medial lobe of the salivary gland of adult female Aedes aegypti mosquitoes, was demonstrated by means of whole-mount fluorescence immunocytochemistry. This innervation originates in the stomatogastric nervous system. 5-HT-immunoreactive innervation is absent in male salivary glands, suggesting that 5-HT is involved in blood-feeding. Furthermore, female mosquitoes treated with the 5-HT-depleting agent alpha-methyltryptophan (AMTP) and then allowed to feed on a rat exhibited a significantly longer mean probing period and a lower blood-feeding success rate than did control mosquitoes. When female mosquitoes were experimentally induced to salivate into mineral oil, AMTP-treated individuals secreted significantly less saliva than did control mosquitoes. These samples of saliva also contained significantly lower concentrations of apyrase, an enzyme important in blood-feeding. Injection of 5-HT into both AMTP-treated and control mosquitoes elicited significant increases in the volume of secreted saliva and/or its apyrase content. We conclude that 5-HT plays an important role in the control of salivation in adult female A. aegypti.
For more than a decade, Bacillus thuringiensis israelensis (Bti) and B. sphaericus have been used successfully as biological control agents against mosquitoes in Germany. Over 1000 km(2) of breeding areas have been treated with Bti, resulting in a yearly reduction of the mosquito population by more than 90%, without evidence of any harmful impact on the environment. Here, Norbert Becker describes the control strategy and operational use of Bti and B. sphaericus in Germany.
Since the incidence of mosquito-borne disease was drastically reduced by the use of DDT in the 1950s, the problem has again worsened and no single method of eradication seems likely to achieve lasting success. It now seems that the best hope lies in the combination of various methods of chemical control and perhaps genetic control to rid the Third World of its most important disease sector.
The impact of the mosquito adulticide naled on honey bees, Apis mellifera L., was evaluated by exposing test beehives to nighttime aerial ultra-low-volume (ULV) applications using a high-pressure nozzle system. The tests were conducted during routine mosquito control missions at Manatee County, Florida, in summer 2000. Two treatment sites were sprayed a total of four times over a 10-wk period. Honey bees, which clustered outside of the hive entrances, were subjected to naled exposure during these mosquito control sprays. The highest average naled ground deposition was 2,688 microg/m2 at the Port Manatee site, which resulted in statistically significant bee mortality (118) compared with the controls. At the Terra Ceia Road site, an intermediate level of naled deposition was found (1,435 microg/m2). For this spray mission, the range of dead bees per hive at Terra Ceia was 2 to 9 before spraying and 5 to 36 after naled application. Means of all other naled ground depositions were < 850 microl/m2. We concluded that substantial bee mortality (> 100 dead bees) resulted when naled residue levels were > 2,000 kg/m2 and honey bees were clustered outside of the hive entrances during mosquito adulticide applications. Compared with the flat-fan nozzle systems currently used by most of Florida's mosquito control programs, the high-pressure nozzle system used in this experiment substantially reduced environmental insecticide contamination and lead to decreased bee mortality. Statistical analysis also showed that average honey yield at the end of the season was not significantly reduced for those hives that were exposed to the insecticide.
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.
The ways in which repellents and attractants could be used to interrupt the transmission of bancroftian filariasis, especially by Culex pipiens fatigans, are assessed. Dimethyl phthalate (DMP) is an effective repellent against C. p. fatigans. It is also very toxic to all larval stages of Wuchereria bancrofti. The median lethal time to microfilariae of a solution of about 0.2% in normal saline is about 10 minutes. Other stages are similarly sensitive. Contact with DMP in very thin films is almost immediately lethal. It is highly unlikely that infection could take place under ordinary conditions through skin treated with DMP for at least many hours afterwards. This toxicity made it impossible to evaluate repellency in vitro. An in vivo test of the effect of skin applications of DMP on microfilaria counts gave anomalous results. A schedule for filariasis control, involving education, garbage disposal, rodent control, sewage disposal, and mosquito control, is proposed, and the research needed to allow repellents and attractants to play a full role in such a schedule is delineated.
Since West Nile virus (WNV) was first recognized in the United States in 1999, the geographic distribution has widened progressively, and the resulting human morbidity and mortality has increased. The cornerstones of WNV control and prevention are 1) surveillance with sustained and integrated mosquito control to detect the presence of WNV in areas where humans are at risk and 2) public education on the use of personal protective behaviors (PPBs) and peridomestic mosquito control to reduce the risk for mosquito bites. In Connecticut, strategies to improve public education and WNV-risk awareness consist of issuing graded warnings after assessing local surveillance findings during the transmission season. In 2002, three of the 17 Connecticut patients with confirmed WNV infection reported having used any PPBs. To assess knowledge, attitudes, and behaviors about WNV during the transmission season, the Connecticut Department of Public Health added questions about WNV to its Behavioral Risk Factor Surveillance System (BRFSS) survey conducted during August-November 2002. This report summarizes the results of that analysis, which indicate that general awareness of WNV and knowledge of elderly persons being at risk for more severe illness were high; however, awareness of local surveillance findings was poor, and belief in the local presence of WNV did not predict the use of PPBs. The findings underscore the need for continued public education about the risk for WNV infection and the use of PPBs and the need for regular systematic evaluations of knowledge, attitudes, and behaviors to refine and improve public health messages effectively.
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