Using adult mosquitoes to transfer insecticides to Aedes aegypti larval habitats.

Vector control is a key means of combating mosquito-borne diseases and the only tool available for tackling the transmission of dengue, a disease for which no vaccine, prophylaxis, or therapeutant currently exists. The most effective mosquito control methods include a variety of insecticidal tools that target adults or juveniles. Their successful implementation depends on impacting the largest proportion of the vector population possible. We demonstrate a control strategy that dramatically improves the efficiency with which high coverage of aquatic mosquito habitats can be achieved. The method exploits adult mosquitoes as vehicles of insecticide transfer by harnessing their fundamental behaviors to disseminate a juvenile hormone analogue (JHA) between resting and oviposition sites. A series of field trials undertaken in an Amazon city (Iquitos, Peru) showed that the placement of JHA dissemination stations in just 3-5% of the available resting area resulted in almost complete coverage of sentinel aquatic habitats. More than control mortality occurred in 95-100% of the larval cohorts of Aedes aegypti developing at those sites. Overall reductions in adult emergence of 42-98% were achieved during the trials. A deterministic simulation model predicts amplifications in coverage consistent with our observations and highlights the importance of the residual activity of the insecticide for this technique

Adaptation and evaluation of the bottle assay for monitoring insecticide resistance in disease vector mosquitoes in the Peruvian Amazon

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to establish whether the "bottle assay", a tool for monitoring insecticide resistance in mosquitoes, can complement and augment the capabilities of the established WHO assay, particularly in resource-poor, logistically challenging environments.</p> <p>Methods</p> <p>Laboratory reared <it>Aedes aegypti </it>and field collected <it>Anopheles darlingi </it>and <it>Anopheles albimanus </it>were used to assess the suitability of locally sourced solvents and formulated insecticides for use with the bottle assay. Using these adapted protocols, the ability of the bottle assay and the WHO assay to discriminate between deltamethrin-resistant <it>Anopheles albimanus </it>populations was compared. The diagnostic dose of deltamethrin that would identify resistance in currently susceptible populations of <it>An. darlingi </it>and <it>Ae. aegypti </it>was defined. The robustness of the bottle assay during a surveillance exercise in the Amazon was assessed.</p> <p>Results</p> <p>The bottle assay (using technical or formulated material) and the WHO assay were equally able to differentiate deltamethrin-resistant and susceptible <it>An. albimanus </it>populations. A diagnostic dose of 10 μg a.i./bottle was identified as the most sensitive discriminating dose for characterizing resistance in <it>An. darlingi </it>and <it>Ae. aegypti</it>. Treated bottles, prepared using locally sourced solvents and insecticide formulations, can be stored for > 14 days and used three times. Bottles can be stored and transported under local conditions and field-assays can be completed in a single evening.</p> <p>Conclusion</p> <p>The flexible and portable nature of the bottle assay and the ready availability of its components make it a potentially robust and useful tool for monitoring insecticide resistance and efficacy in remote areas that require minimal cost tools.</p

CARACTERISTICAS DEL DESOVE DE CHURO, Pomacea maculata EN AMBIENTE CONTROLADO

Se reportan las características de los desoves de "churo", Pomacea maculata, en acuarios de vidrio en Iquitos-Perú. Se utilizaron seis acuarios de vidrio de 70 x 40 x 40 cm. con un tirante de agua de 15 cm. En cada acuario se colocaron cuatro "churos" adultos, proporcionándose alimento peletizado con un tenor de 30% de proteina total y además hierbas acuáticas: "putu-putu", Eichornia crassipes, "lenteja de agua", Salvinia auriculata y "huama", Pistia stratiotes. La oviposición se realizó en las paredes internas de los acuarios a una altura de 15 a 30 cm sobre el nivel del agua. Los desoves presentan una amplia variabilidad, tanto en longitud, como en ancho y espesor (coeficiente variabilidad (c.v) = 15 a 20 %). El desarrollo ontogénico ocurre entre los 12 y 16 días, con una media de 14 días, obteniéndose entre 77 y 483 crías por desove, con un peso individual de 0,028 gramos. El número de crías representa aproximadamente del 44 al 50 % de los huevos en cada puesta

Mosquito-Disseminated Insecticide for Citywide Vector Control and Its Potential to Block Arbovirus Epidemics: Entomological Observations and Modeling Results from Amazonian Brazil

<div><p>Background</p><p>Mosquito-borne viruses threaten public health worldwide. When the ratio of competent vectors to susceptible humans is low enough, the virus’s basic reproductive number (<i>R</i>₀) falls below 1.0 (each case generating, on average, <1.0 additional case) and the infection fades out from the population. Conventional mosquito control tactics, however, seldom yield <i>R</i>₀ < 1.0. A promising alternative uses mosquitoes to disseminate a potent growth-regulator larvicide, pyriproxyfen (PPF), to aquatic larval habitats; this kills most mosquito juveniles and substantially reduces adult mosquito emergence. We tested mosquito-disseminated PPF in Manacapuru, a 60,000-inhabitant city (~650 ha) in Amazonian Brazil.</p><p>Methods and Findings</p><p>We sampled juvenile mosquitoes monthly in 100 dwellings over four periods in February 2014–January 2016: 12 baseline months, 5 mo of citywide PPF dissemination, 3 mo of focal PPF dissemination around <i>Aedes</i>-infested dwellings, and 3 mo after dissemination ended. We caught 19,434 juvenile mosquitoes (66% <i>Aedes albopictus</i>, 28% <i>Ae</i>. <i>aegypti</i>) in 8,271 trap-months. Using generalized linear mixed models, we estimated intervention effects on juvenile catch and adult emergence while adjusting for dwelling-level clustering, unequal sampling effort, and weather-related confounders. Following PPF dissemination, <i>Aedes</i> juvenile catch decreased by 79%–92% and juvenile mortality increased from 2%–7% to 80%–90%. Mean adult <i>Aedes</i> emergence fell from 1,077 per month (range 653–1,635) at baseline to 50.4 per month during PPF dissemination (range 2–117). Female <i>Aedes</i> emergence dropped by 96%–98%, such that the number of females emerging per person decreased to 0.06 females per person-month (range 0.002–0.129). Deterministic models predict, under plausible biological-epidemiological scenarios, that the <i>R</i>₀ of typical <i>Aedes</i>-borne viruses would fall from 3–45 at baseline to 0.004–0.06 during PPF dissemination. The main limitations of our study were that it was a before–after trial lacking truly independent replicates and that we did not measure mosquito-borne virus transmission empirically.</p><p>Conclusions</p><p>Mosquito-disseminated PPF has potential to block mosquito-borne virus transmission citywide, even under adverse scenarios. Our results signal new avenues for mosquito-borne disease prevention, likely including the effective control of <i>Aedes</i>-borne dengue, Zika, and chikungunya epidemics. Cluster-randomized controlled trials will help determine whether mosquito-disseminated PPF can, as our findings suggest, develop into a major tool for improving global public health.</p></div

Monthly estimates of the basic reproductive number (<i>R</i>₀) of mosquito-borne viruses similar to dengue, Zika, or chikungunya.

<p>We considered scenarios ranging from optimistic to very adverse (see parameter values for each scenario in <a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1002213#pmed.1002213.t001" target="_blank">Table 1</a>); the grey line corresponds to the worst-case scenario but with a higher value of the mean daily female mosquito death rate (<i>μ</i> = 0.3 instead of 0.1) to approximate data from wild <i>Ae</i>. <i>aegypti</i> populations (see [<a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1002213#pmed.1002213.ref034" target="_blank">34</a>–<a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1002213#pmed.1002213.ref037" target="_blank">37</a>]). The pink dotted line shows empirical monthly values of the number of <i>Aedes</i> females per person (parameter <i>m</i>) in our study setting and period. The periods of citywide (dark grey) and focal (light grey) PPF dissemination are highlighted on the <i>x</i>-axis.</p

Estimated effects of mosquito-disseminated pyriproxyfen on adult <i>Aedes</i> emergence: results from generalized linear mixed models.

<p>Estimated effects of mosquito-disseminated pyriproxyfen on adult <i>Aedes</i> emergence: results from generalized linear mixed models.</p

Parameter values used to investigate the expected variation of the basic reproductive number, <i>R</i>₀, of a mosquito-borne viral infection as a function of the ratio of emerging <i>Aedes</i> females to humans under five hypothetical scenarios.

<p>Parameter values used to investigate the expected variation of the basic reproductive number, <i>R</i>₀, of a mosquito-borne viral infection as a function of the ratio of emerging <i>Aedes</i> females to humans under five hypothetical scenarios.</p

Monthly female <i>Aedes aegypti</i> emergence in each of the 100 surveillance dwellings.

<p>The distribution of dwellings (black dots) and pyriproxyfen dissemination stations (green dots) is shown in the first panel, where dots are overlaid on a schematic of Manacapuru. In the remaining panels, bubble size is proportional to the number of emerging <i>Ae</i>. <i>aegypti</i> females; the scale is shown as a grey bubble in the second panel. For each month, the total number of emerging <i>Ae</i>. <i>aegypti</i> females is shown in the upper right corner of the panel. Color coding: brown, pre-intervention (baseline) period, with yellow indicating a single-survey month; dark green, citywide PPF dissemination; light green, focal PPF dissemination; blue, post-intervention period, with light blue indicating a single-survey month. Temporal boundaries between periods are highlighted by colored vertical bars.</p

Monthly female <i>Aedes</i> spp. emergence from sentinel breeding sites set in 100 surveillance dwellings, Manacapuru, Amazonas, Brazil, February 2014–January 2016.

<p>Monthly female <i>Aedes</i> spp. emergence from sentinel breeding sites set in 100 surveillance dwellings, Manacapuru, Amazonas, Brazil, February 2014–January 2016.</p

Study site: the city of Manacapuru, state of Amazonas, Brazil.

<p>The black circles indicate the location of the 100 dwellings monitored for mosquito vectors; the green circles indicate the location of the 1,000 pyriproxyfen dissemination stations. Circles are overlaid on a schematic of Manacapuru; locations are approximate. The map of Latin America was drawn using the maps library in R 3.1.2 (<a href="https://www.r-project.org/" target="_blank">https://www.r-project.org/</a>).</p