Estimating contact rates between Metarhizium anisopliae–exposed males with female Aedes aegypti

Introduction: Effective control of Aedes aegypti will reduce the frequency and severity of outbreaks of dengue, chikungunya, and Zika; however, control programs are increasingly threatened by the rapid development of insecticide resistance. Thus, there is an urgent need for novel vector control tools, such as auto-dissemination of the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana. The aim of this study was to estimate contact rates of M. anisopliae-exposed males with wild female Ae. aegypti. As a control the contact rates of untreated males with wild females was contrasted. Methods: The study was conducted in Reynosa, Mexico. The treatment and control households (n = 15 per group) were geographically separated by an arid and hot area that naturally prevented the flight of males between arms. In each control household, 40 M. anisopliae-exposed male Ae. aegypti were released per week for 8 weeks (specimens were exposed to a concentration of 5.96 × 107 conidia/cm2 for 24 h; n = 4,800 males). In each control household, 40 untreated males were released per week for 8 weeks (n = 4,800 males). All specimens were dust-marked prior to release. Mosquito abundance was monitored with human landing collections, and captured Ae. aegypti were examined for any dust-marking. Results: In the treatment households, the contact rate of Ae. aegypti females with marked, fungus-treated males was 14% (n = 29 females marked from 197). Where in the control households, the contact rate of females with marked, untreated males was only 6% (n = 22 marked from 365). In the treatment households the recapture rate of released males was at 5% and higher than that for the control households (which was 2%). Auto-dissemination of M. anisopliae from infected males to female Ae. aegypti was demonstrated through the recovery of an infected female from the floor of a household. Conclusions: Overall, the contact rate between M. anisopliae-infected males with the natural female population was 60% higher than for the control group of healthy males. The results provide further support to the release of fungus-exposed males as a potentially useful strategy against Ae. aegypti, though further research is required

Transmission of Beauveria bassiana from male to female Aedes aegypti mosquitoes

<p>Abstract</p> <p>Background</p> <p>Resistance to chemical insecticides plus high morbidity rates have lead to rising interest in fungi as candidates for biocontrol agents of mosquito vectors. In most studies fungal infections have been induced by exposure of mosquitoes to various surfaces treated with conidia. In the present study eight Mexican strains of <it>Beauveria bassiana </it>were assessed against <it>Aedes aegypti </it>by direct exposure of females to 6 × 10⁸conidia ml ^-1on a filter paper, afterwards, the transmission of the least and most virulent isolates was evaluated by mating behavior from virgin, fungus-contaminated male to females, to examine this ethological pattern as a new approach to deliver conidia against the dengue vector.</p> <p>Methods</p> <p>In an exposure chamber with a filter paper impregnated with 6 × 10⁸conidia ml ^-1of the least and most virulent strains of <it>B. bassiana</it>, 6-8 day old males of <it>A. aegypti </it>were exposed for 48 hours, and then transferred individually (each one was a replicate) to another chamber and confined with twenty healthy females of the same age. Clean males were used in controls. Survival, infection by true mating (insemination) or by mating attempts (no insemination) and fecundity were daily registered until the death of last female. Data analysis was conducted with proc glm for unbalanced experiments and means were separated with the Ryan test with SAS.</p> <p>Results</p> <p>All strains were highly virulent with LT₅₀ranging from 2.70 (± 0.29) to 5.33 (± 0.53) days. However the most (Bb-CBG2) and least virulent (Bb-CBG4) isolates were also transmitted by mating behavior; both killed 78-90% of females in 15 days after being confined with males that had previously been exposed for 48 hours to fungi. Of these mortality rates, 23 and 38% respectively, were infections acquired by copulations where insemination occurred. The LT₅₀for sexually-infected females were 7.92 (± 0.46) and 8.82 (± 0.45) days for both strains, while the one in control was 13.92 (± 0.58). Likewise, fecundity decreased by 95% and 60% for both Bb-CBG2 and Bb-CBG4 isolates in comparison with control. The role of mating attempts in this delivery procedure of <it>B. bassiana </it>is discussed.</p> <p>Conclusions</p> <p>This is the first report about transmission of <it>B. bassiana </it>by mating behavior from virgin, fungus-contaminated males to females in <it>A. aegypti</it>. Fungal infections acquired by this route (autodissemination) infringed high mortality rates (90%) in mated or approached females. However, prior to releasing virgin, fungus-contaminated males to spread <it>B. basasiana </it>among females of <it>A. aegypti</it>, this novel alternative needs further investigations.</p

Aedes albopictus in northeast Mexico: An update on adult distribution and first report of parasitism by Ascogregarina taiwanensis

ABSTRACT Background &amp; objectives: Aedes albopictus has been known as efficient vector of dengue in Asian countries and its wide displacement of Ae. aegypti has been documented in many parts of the world. The present survey was carried out to update the distribution of Ae. albopictus in northeast Mexico and to report the first record of parasitism of mosquitoes by Ascogregarina taiwanensis in Mexico

Dissemination of Metarhizium anisopliae of low and high virulence by mating behavior in Aedes aegypti

<p>Abstract</p> <p>Background</p> <p>Dengue is a viral disease transmitted by <it>Aedes </it>mosquitoes. It is a threat for public health worldwide and its primary vector <it>Aedes aegypti </it>is becoming resistant to chemical insecticides. These factors have encouraged studies to evaluate entomopathogenic fungi against the vector. Here we evaluated mortality, infection, insemination and fecundity rates in <it>A. aegypti </it>females after infection by autodissemination with two Mexican strains of <it>Metarhizium anisopliae</it>.</p> <p>Methods</p> <p>Two <it>M. anisopliae </it>strains were tested: The Ma-CBG-1 least virulent (lv), and the Ma-CBG-2 highly virulent (hv) strain. The lv was tested as non mosquito-passed (NMP), and mosquito-passed (MP), while the hv was examined only as MP version, therefore including the control four treatments were used. In the first bioassay virulence of fungal strains towards female mosquitoes was determined by indirect exposure for 48 hours to conidia-impregnated paper. In the second bioassay autodissemination of fungal conidia from fungus-contaminated males to females was evaluated. Daily mortality allowed computation of survival curves and calculation of the LT₅₀by the Kaplan-Meier model. All combinations of fungal sporulation and mating insemination across the four treatments were analyzed by χ². The mean fecundity was analyzed by ANOVA and means contrasted with the Ryan test.</p> <p>Results</p> <p>Indirect exposure to conidia allowed a faster rate of mortality, but exposure to a fungal-contaminated male was also an effective method of infecting female mosquitoes. All females confined with the hv strain-contaminated male died in fifteen days with a LT₅₀of 7.57 (± 0.45) where the control was 24.82 (± 0.92). For the lv strain, it was possible to increase fungal virulence by passing the strain through mosquitoes. 85% of females exposed to hv-contaminated males became infected and of them just 10% were inseminated; control insemination was 46%. The hv strain reduced fecundity by up to 99%, and the lv strain caused a 40% reduction in fecundity.</p> <p>Conclusions</p> <p>The hv isolate infringed a high mortality, allowed a low rate of insemination, and reduced fecundity to nearly zero in females confined with a fungus-contaminated male. This pathogenic impact exerted through sexual transmission makes the hv strain of <it>M. anisopliae </it>worthy of further research.</p

Generalidades y potencialidad en biocontrol de las gregarinas entomoparásitas

Se presenta una descripciU?n general de la taxonomI?a, ciclo biologico, rango de huespedes y patoge- nicidad de las gregarinas par·sitas de insectos. Se mencionan los factores responsables mas importan- tes que determinan su patogenicidad, usando ejemplos de especies con baja, moderada y alta patogenicidad sobre insectos plaga y vectores de patogenos al hombre. Finalmente, se recomiendan lI?neas de investigacion como una guI?a para estudios futuros orientados hacia el posible uso de estos protozoarios entomoparasitos en biocontrol

CEPAS DE METARHIZIUM ANISOPLIAE PARA EL CONTROL DE MOSQUITOS VECTORES DEL DENGUE

Biotecnologí

The logistic model for predicting the non-gonoactive Aedes aegypti females

Objetivo. Estimar la probabilidad para que una hembra de Aedes aegypti, previamente alimentada con sangre humana, permanezca no gonoactiva, sin madurar huevos, dependiendo del tamaño corporal y tipo de colecta. Material y métodos. Se hicieron 10 muestreos de Ae aegypti.: seis de hembras capturadas en cebo humano, dos de nulíparas y dos colectadas en reposo intradomiciliar. Cada muestreo incluyó 60 hembras, en tres colonias endémicas para dengue, en Monterrey, Nuevo León, México, entre 1994 y 1996. Las hembras grávidas o con sangre en estómago fueron excluidas. Cada mosquito fue llevado al laboratorio y alimentado a repleción con sangre humana, y a las 48 horas los ovarios fueron disecados para registrar si estaban en fase gonoactiva o no. El tamaño corporal fue registrado por la longitud en mm del ala izquierda de cada mosquito. Se usó regresión logística para estimar la probabilidad de que una hembra fuera no gonoactiva, como una variable binaria, en función de la longitud alar, y del tipo de colecta. Resultados. De las 600 hembras procesadas, 164 (27%) permanecieron no gonoactivas, y su tamaño corporal mostró un intervalo (1.9-3.2 mm) casi igual al total de las hembras (1.8-3.3 mm). El modelo de regresión logística fue significativo para estimar la probabilidad de que una hembra permanezca no gonoactiva (Y=1). El tipo de colecta no tuvo influencia significativa en la variable binaria, pero la probabilidad de no gonoactividad mostró una relación inversa con el tamaño corporal. Conclusiones. Las poblaciones del vector del dengue en Monterrey, México, están integradas por hembras de tamaño muy variable. La regresión logística resultó útil para evaluar la probabilidad que tiene una hembra de quedar no gonoactiva después de una alimentación sanguínea. La necesidad de una segunda comida sanguínea está presente en cualquier mosquito, pero los pequeños tienen una mayor probabilidad de picar por segunda ocasión a una persona en un periodo de dos días, para poder madurar huevos

Collections of sandflies (diptera:psychodidae) from mammal burrows in an area of cutaneous leishmaniasis in Campeche, México

Sand flies were caught from December 1993 to November 1994 in an endemic focus of cutaneous leishmaniasis in the state of Campeche, Mexico. A total of 566 sand flies of seven species were collected using emergence funnel-traps, at openings of several mammal burrows. The main species collected were Lutzomyia deleoni and Brumptomyia hamata. Population abundance was found bimodal with the first and higher peak from January to March. A small second peak was found from May to October

Localización de criaderos no-residenciales de aedes aegypti y su asociación con casos de dengue en la zona metropolitana de Monterrey, Nuevo León, México

El dengue y sus variantes clásico y hemorrágico continúan incrementándose en México y representan un serio problema de salud pública. El desplazamiento del mosquito Vector Aedes aegypti de los domicilios humanos donde típicamente se ha encontrado hacia lotes baldíos, mercados, parques públicos y patios de empresas con bajos niveles de limpieza plantean un desafío a los actuales métodos de control enfocados únicamente a casas. La presente investigación tuvo como objetivos 1) evaluar la presencia de criaderos del mosquito vector en zonas no residenciales así como 2) determinar la adaptabilidad de poblaciones del vector durante la temporada de invierno pues este dato es desconocido e importante para conocer más de la epidemiología del dengue y, 3) integrar la plataforma Google Earth como una herramienta novedosa útil en la epidemiología de la transmisión de la enfermedad. A través de muestreos de campo, se colectaron datos desde Diciembre 2007 hasta Marzo 2008. Estas revisiones de recipientes con agua almacenada y actividad larvaria se concentraron en zonas no residenciales como empresas de Monterrey, San Nicolás, Apodaca, Guadalupe y Escobedo (Nuevo León, México). De un total de 87 sitios muestreados, el 100% presentaron las características de cercanía a zonas habitacionales o vecindades con reportes de dengue. Los propietarios del estos lugares registraron 10% de casos de dengue entre su personal mientras que las casas cercanas reportaron 70% con al menos un caso de dengue registrada durante la epidemia del 2007. Una encuesta de estos lugares con diferente giro comercial indicó que de las actividades de control que llevó a cabo la Secretaría de Salud de Nuevo León (México), solo en 18% de aplicó Temefós 1% granular o Abate, en 8% se fumigó pero en la mayoría, 74%, no se realizó ninguna acción. Se encontraron en total 222 criaderos en los 87 lugares no residenciales visitados. En la mayoría o, 90%, los criaderos estuvieron secos, mientras que solo en 7% se encontraron criaderos activos con agua. Solo 3% de los lugares muestreados fueron negativos a la presencia de criaderos. Estos resultados describen la adaptación y dominancia del mosquito del dengue en nuevos criaderos de zonas no residenciales, su resistencia a las temporadas frías del Invierno, y por consecuencia el riesgo entomológico para futuras epidemias de dengue en el área metropolitana de Monterrey