The resting behavior of Aedes aegypti (L.) adults was investigated in 14 districts of Panama City, Panama, in relation to ground ultra-low volume (ULV) applications of malathion. Adults primarily rested inside the premises (75.1%) at a distance Ͼ6 m from the street (86.4%). Both sexes rested mainly in bedrooms, living rooms, and bathrooms. The small ULV aerosol droplets (2Ð 4 m) penetrated all indoor resting sites of Ae. aegypti, but in low amounts. Because of the low amount of insecticide reaching the primary resting sites within the premises, limited control of the Ae. aegypti was obtained. This limited the potential effectiveness of ground vehicle ULV applied insecticide as a dengue epidemic control method.KEY WORDS Aedes aegypti, culicidae, resting behavior, ultra-low volume insecticides DURING THE 1950S and 1960s, Ͼ20 countries in the Americas were able to eradicate Aedes aegypti (L.), but in the last 20 yr, almost every one of these countries including Panama has become reinfested and has had sizable epidemics of dengue fever (Gubler and Kuno 1997). Although future outbreaks of dengue fever may be avoided by eliminating larval habitats through community participation, there are still areas with Ae. aegypti infestation that may allow outbreaks of the disease. For this reason, emergency measures must be available for use in future dengue outbreaks.The intervention used during epidemics is the ground application of small quantities of aerosol insecticide (ultra-low volume or ULV). Elsewhere, ULV applications have been shown repeatedly to give Ͻ100% control of adult Ae. aegypti populations (Hudson 1986, Focks et al. 1987, Perich et al. 1990. One reason for this reduced effectiveness is Ae. aegypti resting behavior. A portion of the population is found in wardrobes, under beds, behind furniture and in closed rooms where it is difÞcult for aerosol droplets to reach. Focks et al. (1987) hypothesized that gravid females remain sequestered during treatment periods in places that are well-protected from aerosols.Schoof (1967) indicated that the resting habits of this mosquito are relatively unknown, but suggested that adults gather at breeding places, resting there and on adjoining surfaces. In Thailand, Pant and Yasuno (1970) demonstrated that 95% of the mosquitoes rest indoors, and of these, Ͼ90% did so on surfaces that could not be sprayed with residual compounds, such as clothing, pictures, decorative objects, coverlets, and mosquito nets. This Þnding indicated that it was of little value to use residual insecticides on indoor walls. Nelson (1986) reported that mosquitoes rested indoors most frequently in bedrooms, bathrooms, and kitchens where they preferred vertical surfaces such as walls, furniture, and hanging articles such as clothing, towels, curtains, and mosquito nets, although they also were found on the ceiling and under furniture such as beds.Detailed investigation of the resting behavior of Ae. aegypti is needed if chemical control is to be adopted for the control of adult mosquitoes. In th...
BackgroundThe persistence of Triatoma infestans and the continuous transmission of Trypanosoma cruzi in the Inter-Andean Valleys and in the Gran Chaco of Bolivia are of great significance. Coincidentally, it is in these regions the reach of the vector control strategies is limited, and reports of T. infestans resistance to insecticides, including in wild populations, have been issued. This study aims to characterize the susceptibility to deltamethrin of wild and domestic populations of T. infestans from Bolivia, in order to better understand the extent of this relevant problem.MethodsSusceptibility to deltamethrin was assessed in nine, wild and domestic, populations of T. infestans from the Gran Chaco and the Inter-Andean Valleys of Bolivia. Serial dilutions of deltamethrin in acetone (0.2 μL) were topically applied in first instar nymphs (F1, five days old, fasting, weight 1.2 ± 0.2 mg). Dose response results were analyzed with PROBIT version 2, determining the lethal doses, slope and resistance ratios (RR). Qualitative tests were also performed.ResultsThree wild T. infestans dark morph samples of Chaco from the Santa Cruz Department were susceptible to deltamethrin with RR50 of <2, and 100% mortality to the diagnostic dose (DD); however, two domestic populations from the same region were less susceptible than the susceptibility reference lineage (RR50 of 4.21 and 5.04 respectively and 93% DD). The domestic population of Villa Montes from the Chaco of the Tarija Department presented high levels of resistance (RR50 of 129.12 and 0% DD). Moreover, the domestic populations from the Valleys of the Cochabamba Department presented resistance (RR50 of 8.49 and 62% DD), the wild populations were less susceptible than SRL and T. infestans dark morph populations (RR50 < 5).ConclusionThe elimination of T. infestans with pyrethroid insecticides in Brazil, Uruguay, Chile, and its drastic reduction in large parts of Paraguay and Argentina, clearly indicates that pyrethroid resistance was very uncommon in non-Andean regions. The pyrethroid susceptibility of non-Andean T. infestans dark morph population, and the resistance towards it, of Andean T. infestans wild and domestic populations, indicates that the Andean populations from Bolivia are less susceptible.
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