RESUMO

In the sterile insect technique, it is important to measure the impact of mass-rearing and handling of sterile males to allow a successful control of the target wild population. This study evaluates the effect of pre-release chilling on the survival, escape ability, and sexual competitiveness of male Aedes aegypti. To determine survival and escape ability, mosquitoes were chilled at 4 °C using four different treatments of either one exposure (25 min) or two consecutive exposures (25 + 25 min, 25 + 50 min, 25 + 100 min). For sexual competitiveness, two different treatments were evaluated, chilling for 25 min once and twice. Results showed that the longest exposure to chilling caused a significant reduction of survival time, from 67 to 54 days. Escape ability was reduced by the first chilling from 25 to 7% and with the second chilling, it was reduced from 30 to 24% in the control to 4.9, 2.0 and 0.5% for 25, 50 and 100 min, respectively. Sexual competitiveness index was reduced from 1.16 in the control, to 0.32 and - 0.11 for treatments involving one and two chilling periods, respectively. It is recommended to increase the chilling temperature and reduce the exposure time to reduce the harmful effects on sterile males.

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RESUMO

Worldwide, vector-transmitted diseases account for more than 17% of all infectious diseases and cause more than 700,000 deaths annually. The primary strategy to control the transmission of dengue, chikungunya and Zika focuses on the control of their vectors. Vector control programs depend mainly on the use of insecticides. However, these measures have failed to yield the desired results because the lack of proper control decreases their effectiveness over time. Also, the effect of insecticide use on non-target organisms, environmental contamination, and the development of insecticide resistance impose continuous challenges for insecticide-dependant control programs. The sterile insect technique, on the other hand, is a non-polluting and environment-friendly technique. The use of sterile insects is generally well established in agriculture, but human health interventions often require a consensus that combines social perceptions with scientific evidence. Factors associated with acceptance of the releases of sterile male Aedes aegypti mosquitoes were assessed with logistic regression models for two communities (Rio Florido and Hidalgo) in Tapachula, Chiapas, Mexico. The favourable opinion of the respondents about the project workers, and the fact that the releases of sterile mosquitoes would be managed by the Secretaría de Salud, were found to be factors that supported the acceptance of sterile mosquito releases. Factors associated with disapproval were community (Rio Florido and Hidalgo) and the misbelief that sterile male mosquitoes can bite. The differences observed between the communities included in this study might be the result of experiences with the releases, of social and community organisation, and of leadership by social actors.

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The objective of this study was to analyze the effect of the rural and urban microclimate on the presence of mosquitoes. Temperature (T) and relative humidity (RH; indoors and outdoors), as well as mosquito richness and abundance were measured in two sites (urban and rural) of the Yucatan State, Mexico. Species richness was higher in the urban site, whereas mosquito abundance was higher in the rural site. The microclimates of urban and rural housing differently affect mosquito richness and abundance. Mosquito richness and abundance were higher outdoors than indoors in the urban site, but they were higher indoors than outdoors in the rural site. For the urban site, analysis of the relation of T and RH with the registered parameters revealed that species richness increased with increasing indoor RH, and that mosquito abundance increased with increasing indoor T and RH. In the rural site, species richness was not affected, but abundance increased with increasing T and RH (indoors as well as outdoors). Results are discussed in the context of the management of mosquito transmitted diseases. No IRB approval was necessary since no ethical implications were identified to be reviewed by the ethical committee for the research of the ECOSUR Institution.

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Sterile males of Aedes aegypti were released once a week for 8 weeks to evaluate the dispersal efficiency of ground and aerial drone release methods in a rural village of 26 Ha in southern Mexico. Indoor and outdoor BG-Sentinel traps were placed in 13−16 houses distributed throughout the village. The BG traps were activated 48 h after the release of the sterile males and functioned for a 24 h period following each release. Over the 8-week period of simultaneous ground and aerial releases, an average of 85,117 ± 6457 sterile males/week were released at ground level and 86,724 ± 6474 sterile males/week were released using an aerial drone. The ground release method resulted in higher numbers of captured males (mean = 5.1 ± 1.4, range 1.1−15.7 sterile males/trap) compared with the aerial release method (mean = 2.6 ± 0.8, range 0.5−7.3 sterile males/trap) (p < 0.05). Similarly, the prevalence of traps that captured at least one sterile male was significantly higher for ground release compared to the aerial release method (p < 0.01). The lower numbers of sterile males captured in the aerial release method could be due to mortality or physical injury caused by the chilling process for immobilization, or the compaction of these insects during transport and release. However, aerial releases by a two-person team distributed insects over the entire village in just 20 min, compared to ~90 min of work for a five-person team during the ground release method. Ground release also resulted in higher aggregations of males and some villagers reported feeling discomfort from the presence of large numbers of mosquitoes in and around their houses. We conclude that modifications to the handling and transport of sterile males and the design of containers used to store males are required to avoid injury and to improve the efficiency of aerial releases for area-wide SIT-based population suppression programs targeted at mosquito vectors of human disease.

RESUMO

The sterile insect technique may prove useful for the suppression of mosquito vectors of medical importance in regions where arboviruses pose a serious public health threat. In the present study, we examined the effects of sterilizing irradiation doses across different ratios of fertile:irradiated males on the mating competitiveness of Ae. aegypti and Ae. albopictus under laboratory and field-cage conditions. For both species, the percentage of females inseminated and the number of eggs laid over two gonotrophic cycles varied significantly in mating treatments involving 1:1, 1:5, and 1:10 fertile:irradiated males compared to controls of entirely fertile or entirely irradiated males but was not generally affected by the irradiation dose. Egg hatching was negatively affected in females exposed to increasing proportions of irradiated males in both laboratory and field cages. Male competitiveness (Fried's index) values varied from 0.19 to 0.58 in the laboratory and were between 0.09 and 1.0 in field cages, depending on th species. Competitiveness values were negatively affected by th eirradiation dose in both species under field-cage conditions, whereas in the laboratory, Ae. albopictus was sensitive to the dose but Ae. aegypti was not. In general, male competitiveness was similar across all mating regimes. Most importantly, induced egg sterility was positively correlated with the proportion of irradiated males present in the mating treatments, reaching a maximum of 88% under field-cage conditions for both Ae. aegypti and Ae. albopictus males treated with 50 and 40 Gy irradiation, respectively. These results indicate that sterile males produced at our facility are suitable and competitive enough for field pilot SIT projects and provide guidance to decide the optimal sterile:fertile ratios.

RESUMO

Indoor and outdoor ovitraps were placed in 15 randomly selected houses in two rural villages in Chiapas, southern Mexico. In addition, ovitraps were placed in five transects surrounding each village, with three traps per transect, one at the edge, one at 50 m, and another at 100 m from the edge of the village. All traps were inspected weekly. A transect with eight traps along a road between the two villages was also included. Population fluctuations of Aedes aegypti and Ae. albopictus were examined during 2016-2018 by counting egg numbers. A higher number of Aedes spp. eggs was recorded at Hidalgo village with 257,712 eggs (60.9%), of which 58.1% were present in outdoor ovitraps and 41.9% in indoor ovitraps, compared with 165,623 eggs (39.1%) collected in the village of Río Florido, 49.0% in outdoor and 51.0% in indoor ovitraps. A total of 84,047 eggs was collected from ovitraps placed along transects around Río Florido, compared to 67,542 eggs recorded from transects around Hidalgo. Fluctuations in egg counts were associated with annual variation in precipitation, with 2.3 to 3.2-fold more eggs collected from ovitraps placed in houses and 4.8 to 5.1-fold more eggs in ovitraps from the surrounding transects during the rainy season than in the dry season, respectively. Aedes aegypti was the dominant species during the dry season and at the start of the rainy season in both villages. Aedes albopictus populations were lower for most of the dry season, but increased during the rainy season and predominated at the end of the rainy season in both villages. Aedes albopictus was also the dominant species in the zones surrounding both villages. The numbers of eggs collected from intradomiciliary ovitraps were strongly correlated with the numbers of eggs in peridomiciliary ovitraps in both Río Florido (R2 adj = 0.92) and Hidalgo (R2 adj = 0.94), suggesting that peridomiciliary sampling could provide an accurate estimate of intradomiciliary oviposition by Aedes spp. in future studies in these villages. We conclude that the feasibility of sterile insect technique (SIT)-based program of vector control could be evaluated in the isolated Ae. aegypti populations in the rural villages of our baseline study.

RESUMO

The proliferation of arboviruses and their vectors is influenced by a complex interplay between vector, environment and human behaviors. The aim of this work is to analyze the influence of socio-environmental determinants on knowledge and practices regarding arboviruses transmission, among the residents of three communities on the southern border of Mexico. Between June 2017 and August 2018, a set of 149 households from three communities of Tapachula (Chiapas) and Villahermosa (Tabasco) were covered. This study consists of the application of a community prevention project. Different surveys and methodological approaches were used. Associations between socio-environmental determinants and knowledge and practices for arboviruses transmission control were estimated by odds ratio. Logistic regression and qualitative techniques were used. Although around 75% of households had an adequate knowledge about arboviruses' origin and transmission, only 30% of them adopted adequate practices. Domestic risk practices were associated with serious deficiencies in water and sanitation services. Furthermore, a perception of greater risk and difficulty in complying with preventive measures were detected. An adequate knowledge does not necessarily lead to adequate prevention practices. Intermediate social determinants influence on the persistence of risk behaviors for arboviruses proliferation. Addressing such related aspects requires the achievement of an effective and sustainable vector management.

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RESUMO

The Sterile Insect Technique (SIT) is a pest control method where large numbers of sterile males are released to induce sterility in wild populations. Since a successful SIT application depends on the released sterile males being competitive with wild males, standard quality control tests are a necessary component of any SIT program. Flight ability (ability to fly out from a device) is a reliable indicator of insect quality. Based on previous studies, we developed four new tubular devices constructed with locally available materials to explore their potential as flight test devices for Aedes aegypti (L.) mass-reared males. Males were allowed to fly upwards through a vertical tube, the ones that flew out were considered successful. The effect of male age (0 to 21 d old), test time interval (30 min to 24 h), and the design of the device (40 and 80 cm height and 2 and 3.5 cm diameter) were evaluated. Our devices determined differences in the flight ability of Ae. aegypti males of different ages. During the first minutes, more old males escaped than young males in three out of four types of devices. However, young males reached higher rates of escape in all cases after 24 h. For standard quality control tests, we recommend testing 2- to 3-d-old sexually mature males in the high and narrow device (80 × 2 cm). Further observations for time intervals between 1 and 5 h might be performed to decide the shortest and more representative interval to use.

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RESUMO

Abstract: The proliferation of arboviruses and their vectors is influenced by a complex interplay between vector, environment and human behaviors. The aim of this work is to analyze the influence of socio-environmental determinants on knowledge and practices regarding arboviruses transmission, among the residents of three communities on the southern border of Mexico. Between June 2017 and August 2018, a set of 149 households from three communities of Tapachula (Chiapas) and Villahermosa (Tabasco) were covered. This study consists of the application of a community prevention project. Different surveys and methodological approaches were used. Associations between socio-environmental determinants and knowledge and practices for arboviruses transmission control were estimated by odds ratio. Logistic regression and qualitative techniques were used. Although around 75% of households had an adequate knowledge about arboviruses' origin and transmission, only 30% of them adopted adequate practices. Domestic risk practices were associated with serious deficiencies in water and sanitation services. Furthermore, a perception of greater risk and difficulty in complying with preventive measures were detected. An adequate knowledge does not necessarily lead to adequate prevention practices. Intermediate social determinants influence on the persistence of risk behaviors for arboviruses proliferation. Addressing such related aspects requires the achievement of an effective and sustainable vector management.

Resumen: La proliferación de los arbovirus y sus vectores está influenciada por la interacción compleja entre vectores, medio ambiente y comportamientos humanos. El objetivo de este estudio es analizar la influencia de los determinantes socioambientales sobre el conocimiento y las prácticas relacionadas con la transmisión de los arbovirus entre los residentes de tres comunidades en la frontera sur de México. Entre junio de 2017 y agosto de 2018, se estudiaron 149 domicilios en las comunidades de Tapachula (Chiapas) y Villahermosa (Tabasco). El estudio tuvo como base la aplicación de un proyecto de prevención comunitaria, utilizando diferentes encuestas y abordajes metodológicos. Se usaron odds ratios para estimar las asociaciones entre determinantes socioambientales y el conocimiento y prácticas para el control de la transmisión de los arbovirus, con el uso de regresión logística y técnicas cualitativas. Cerca de un 75% de los domicilios mostraban conocimiento adecuado sobre el origen y transmisión de los arbovirus, pero solamente un 30% habían adoptado prácticas apropiadas. Las prácticas de riesgo en los domicilios estaban asociadas a deficiencias significativas en los servicios de saneamiento y abastecimiento de agua. Además, se detectó la percepción de un mayor riesgo y de dificultad en adoptar medidas preventivas. El conocimiento adecuado no necesariamente conduce a prácticas preventivas adecuadas. Los determinantes sociales intermedios influencian la persistencia de comportamientos que actúan como factores de riesgo para la proliferación de los arbovirus. La gestión de vectores eficaz y sostenible es necesaria para lidiar con esos aspectos interrelacionados.

Resumo: A proliferação dos arbovírus e seus vetores é influenciada pela interação complexa entre vetores, meio ambiente e comportamentos humanos. O objetivo do estudo é de analisar a influência dos determinantes socioambientais sobre o conhecimento e as práticas relacionados à transmissão dos arbovírus entre os residentes de três comunidades na fronteira sul do México. Entre junho de 2017 e agosto de 2018, foram estudados 149 domicílios nas comunidades de Tapachula (Chiapas) e Villahermosa (Tabasco). O estudo teve como base a aplicação de um projeto de prevenção comunitária, utilizando diferentes inquéritos e abordagens metodológicas. Foram usadas odds ratios para estimar as associações entre determinantes socioambientais e conhecimento e práticas para controle da transmissão dos arbovírus, com o uso de regressão logística e técnicas qualitativas. Cerca de 75% dos domicílios mostravam conhecimento adequado sobre a origem e transmissão dos arbovírus, mas apenas 30% haviam adotado práticas apropriadas. As práticas de risco nos domicílios estavam associadas a deficiências significativas nos serviços de saneamento e abastecimento de água. Além disso, foi detectada a percepção de maior risco e de dificuldade em adotar medidas preventivas. O conhecimento adequado não necessariamente leva a práticas preventivas adequadas. Os determinantes sociais intermediários influenciam a persistência de comportamentos que agem como fatores de risco para a proliferação dos arbovírus. A gestão de vetores eficaz e sustentável é necessária para lidar com esses aspectos interrelacionados.

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RESUMO

The sterile insect technique (SIT) may offer a means to control the transmission of mosquito borne diseases. SIT involves the release of male insects that have been sterilized by exposure to ionizing radiation. We determined the effects of different doses of radiation on the survival and reproductive capacity of local strains of Aedes aegypti and Ae. albopictus in southern Mexico. The survival of irradiated pupae was invariably greater than 90% and did not differ significantly in either sex for either species. Irradiation had no significant adverse effects on the flight ability (capacity to fly out of a test device) of male mosquitoes, which consistently exceeded 91% in Ae. aegypti and 96% in Ae. albopictus. The average number of eggs laid per female was significantly reduced in Ae. aegypti at doses of 15 and 30 Gy and no eggs were laid by females that had been exposed to 50 Gy. Similarly, in Ae. albopictus, egg production was reduced at doses of 15 and 25 Gy and was eliminated at 35 Gy. In Ae. aegypti, fertility in males was eliminated at 70 Gy and was eliminated at 30 Gy in females, whereas in Ae. albopictus, the fertility of males that mated with untreated females was almost zero (0.1%) in the 50 Gy treatment and female fertility was eliminated at 35 Gy. Irradiation treatments resulted in reduced ovary length and fewer follicles in both species. The adult median survival time of both species was reduced by irradiation in a dose-dependent manner. However, sterilizing doses of 35 Gy and 50 Gy resulted in little reduction in survival times of males of Ae. albopictus and Ae. aegypti, respectively, indicating that these doses should be suitable for future evaluations of SIT-based control of these species. The results of the present study will be applied to studies of male sexual competitiveness and to stepwise evaluations of the sterile insect technique for population suppression of these vectors in Mexico.

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