Mass irradiation of adult Aedes mosquitoes using a coolable 3D printed canister.

In the last decade, the use of the sterile insect technique (SIT) to suppress mosquito vectors have rapidly expanded in many countries facing the complexities of scaling up production and procedures to sustain large-scale operational programs. While many solutions have been proposed to improve mass production, sex separation and field release procedures, relatively little attention has been devoted to effective mass sterilization of mosquitoes. Since irradiation of pupae en masse has proven difficult to standardise with several variables affecting dose response uniformity, the manipulation of adult mosquitoes appears to be the most promising method to achieve effective and reliable sterilization of large quantities of mosquitoes. A 3D-printed phase change material based coolable canister was developed which can compact, immobilize and hold around 100,000 adult mosquitoes during mass radio sterilization procedures. The mass irradiation and compaction treatments affected the survival and the flight ability of Aedes albopictus and Aedes aegypti adult males but the use of the proposed irradiation canister under chilled conditions (6.7-11.3 °C) significantly improved their quality and performance. The use of this cooled canister will facilitate adult mass irradiation procedures in self-contained irradiators in operational mosquito SIT programmes.

Effects of Chilling and Anoxia on the Irradiation Dose-Response in Adult Aedes Mosquitoes.

The success of the sterile insect technique (SIT) relies on the achievement of high levels of sterility and mating success of the factory-reared sterile males and thus their biological quality, which can be enhanced by the reduction of stress factors encountered during rearing, handling, and irradiation procedures. The achievement of consistent sterility levels requires reliable and standard irradiation protocols. Additionally, mosquito adults require immobilization prior to, and during irradiation to increase processing efficiency and to avoid physical damage caused by movement in restricted space. Common methods for immobilization include chilling and anesthetics such as nitrogen. Here we assessed the effects of chilling and exposure to nitrogen on the irradiation dose-response of Aedes mosquitoes, and their downstream effects on some male quality parameters including longevity and flight ability. We found that chilling does not incur damage in the insects in terms of longevity and flight ability when chilling duration and temperature are carefully controlled, and a recovery phase is provided. Irradiation in nitrogen shows high radioprotective effects during irradiation, resulting in reduced induction of sterility. Overall, longevity of males can be improved by irradiating in anoxia, however the exposure to nitrogen itself comes with negative impacts on flight ability. The results reported here will assist in the standardization and optimization of irradiation protocols for the SIT to control mosquito populations of medical relevance.

The efficiency of a new automated mosquito larval counter and its impact on larval survival.

To achieve consistent and standardized rearing for mosquito immature stages, it is crucial to control the initial number of larvae present in each larval tray. In addition, maintaining an optimal and synchronized development rate of larvae is essential to maximize the pupal production and optimize male sorting in a mass-rearing setting. Manual counting is labor intensive, time consuming and error prone. Therefore, this study aimed to investigate the use of a customized automated counter for the quantification of mosquito larvae. The present prototype of the mosquito larval counter uses a single counting channel consisting of three parts: a larvae dispenser, an electronic counting unit and computer control software. After the separation of the larvae from eggs and debris, batches of different numbers of Aedes aegypti first instar larvae were manually counted and introduced into the counter through the upper loading funnel and channeled out from the bottom of the counter by gravitational flow. The accuracy and repeatability of the mosquito larval counter were determined in relation to larval density and water quality. We also investigated its impact on larval survival. Results showed an impact of larval density and water quality on the accuracy of the device. A -6% error and a repeatability of +/- 2.56% average value were achieved with larval densities up to 10 larvae/mL of clean water. Moreover, the use of the mosquito larval counter did not have any effect on larval survival or development. Under recommended conditions, the mosquito larval counter can be used to enumerate the number of mosquito larvae at a given density. However, future developments involving the use of multiple channels or larger input larvae container would help to expand its use in large-scale facilities.

Occurrence of natural Anopheles arabiensis swarms in an urban area of Bobo-Dioulasso City, Burkina Faso, West Africa.

The swarming behaviour of natural populations of Anopheles arabiensis was investigated by conducting transect surveys on 10 consecutive days, around dusk, from March to April and from September to October 2012 in Dioulassoba, a district of Bobo-Dioulasso city in Burkina Faso (West Africa). Swarms were observed outside, around identified larval breeding sites on the banks of the Houet River, as well as in the open-air courtyards found at the centre of many homes in the region. Swarms were found to occur in open sunlit spaces, mostly located above physical or visual cues somehow visually distinct from the surrounding area. Overall 67 and 78 swarms were observed, respectively, during the dry season (March-April) and the rainy season (September-October) of 2012, between 1.5m and 4.5m above the ground at their centre. 964 mosquitoes were collected and analysed from dry season swarms, of which most were male, and all were An. arabiensis, as were the few resting mosquitoes collected indoors. Larvae collected from breeding sites found on the banks of the Houet River mostly consisted of An. arabiensis and only a minority of Anopheles coluzzii (formerly identified as An. gambiae M form). Of 1694 mosquitoes analysed from 78 swarms in the rainy season collections, a few An. gambiae (formerly known as An. gambiae S form) males were identified, and the remainders were An. arabiensis. The majority of larvae collected during the wet season from the same breeding sites were identified as An. arabiensis followed by An. coluzzii and An. gambiae. The same pattern of species composition was observed in resting mosquitoes, though the proportion of An. arabiensis was less overwhelming. These data support the conclusion that An. arabiensis is the most prevalent species in this area, though the difference in species composition when using different population sampling techniques is noteworthy. Further studies are required for more detailed investigations of male dispersal, feeding behaviour and mating patterns in this urban setting.