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The developmental stage of the mosquito is one of the main factors that affect its response to ionizing radiation. Irradiation of adults has been reported to have beneficial effects. However, the main challenge is to immobilize and compact a large number of adult male mosquitoes for homogenous irradiation with minimal deleterious effects on their quality. The present study investigates the use of nitrogen in the irradiation of adult Aedes albopictus and Ae. aegypti. Irradiation in nitrogen (N2) and in air after being treated with nitrogen (PreN2) were compared with irradiation in air at gamma radiation doses of 0, 55, 70, 90, 110, and 125 Gy. In both species, approximately 0% egg hatch rate was observed following doses above 55 Gy in air versus 70 Gy in PreN2 and 90 Gy in N2. Males irradiated at a high mosquito density showed similar egg hatch rates as those irradiated at a low density. Nitrogen treatments showed beneficial effects on the longevity of irradiated males for a given dose, revealing the radioprotective effect of anoxia. However, irradiation in N2 or PreN2 slightly reduced the male flight ability. Nitrogen treatment was found to be a reliable method for adult mosquito immobilization. Overall, our results demonstrated that nitrogen may be useful in adult Aedes mass irradiation. The best option seems to be PreN2 since it reduces the immobilization duration and requires a lower dose than that required in the N2 environment to achieve full sterility but with similar effects on male quality. However, further studies are necessary to develop standardized procedures including containers, time and pressure for flushing with nitrogen, immobilization duration considering mosquito species, age, and density.

The production of a large number of mosquitoes of high biological qualities and reliable sex sorting before release are key challenges when applying the sterile insect technique as part of an area-wide integrated pest management approach. There is a need to fully evaluate the production capacity of the equipment developed in order to plan and maintain a daily production level for large-scale operational release activities. This study aimed to evaluate the potential use of the FAO/IAEA larval rearing unit for Aedes aegypti and the subsequent female contamination rate after sex sorting with a Fay-Morlan glass separator. Trays from each rack were tilted and their contents sorted either for each individual tray or after mixing the content of all trays from the rack. The pupal production and the female contamination rate were estimated with respect to day of collection, position of the tray, type of pupae collection, and sorting operator. Results showed significant daily variability of pupal production and female contamination rate, with a high male pupal production level achieved on the second day of collection and estimated female contamination of male pupae reached around 1%. Neither tray position nor type of pupae collection affected the pupal production and female contamination rate. However, the operator had a significant effect on the female contamination rate. These results highlight the need to optimize pupal production at early days of collection and to develop a more effective and automated method of sex separation.; La production d’un grand nombre de moustiques de haute qualité biologique et le tri des sexes avant les lâchers sont des défis clés lors de l’application de la technique des insectes stériles, dans le cadre d’une approche de lutte intégrée contre les ravageurs à l’échelle d’une zone. Il est nécessaire d’évaluer pleinement la capacité de production des équipements développés afin de planifier et de maintenir un niveau de production quotidien pour les activités de libération opérationnelle à grande échelle. Cette étude visait à évaluer l’utilisation potentielle de l’unité d’élevage larvaire FAO/AIEA pour Aedes aegypti et le taux de contamination par des femelles après le tri sexuel avec un séparateur en verre Fay–Morlan. Les plateaux de chaque rack ont été inclinés et leur contenu trié soit pour chaque plateau, soit après avoir mélangé le contenu de tous les plateaux du rack. La production de pupes et le taux de contamination par des femelles ont été estimés en fonction du jour de collecte, de la position du bac, du type de collecte des pupes et de l’opérateur du tri. Les résultats ont montré une variabilité quotidienne significative de la production de pupes et du taux de contamination par des femelles, avec un niveau élevé de production de pupes mâles atteint le deuxième jour de collecte et la contamination estimée des pupes mâles par des femelles a atteint environ 1 %. Ni la position du plateau ni le type de collecte des pupes n’ont affecté la production de pupes et le taux de contamination par des femelles. Cependant, l’opérateur avait un effet significatif sur le taux de contamination par les femelles. Ces résultats mettent en évidence la nécessité d’optimiser la production des pupes dès les premiers jours de la collecte et de développer une méthode de séparation des sexes plus efficace et automatisée.

The sterile insect technique is a promising environmentally friendly method for mosquito control. This technique involves releasing laboratory-produced sterile males into a target field site, and its effectiveness may be affected by the extent of adult mosquito predation. Sterile males undergo several treatments. Therefore, it is vital to understand which treatments are essential in minimizing risks to predation once released. The present study investigates the predation propensity of four mantis species (Phyllocrania paradoxa, Hymenopus coronatus, Blepharopsis mendica, Deroplatys desiccata) and two gecko species (Phelsuma standingi, P. laticauda) on adult Aedes aegypti, Ae. albopictus and Anopheles arabiensis mosquitoes in a laboratory setting. First, any inherent predation preferences regarding mosquito species and sex were evaluated. Subsequently, the effects of chilling, marking, and irradiation, on predation rates were assessed. The selected predators effectively preyed on all mosquito species regardless of the treatment. Predation propensity varied over days for the same individuals and between predator individuals. Overall, there was no impact of laboratory treatments of sterile males on the relative risk of predation by the test predators, unless purposely exposed to double the required sterilizing irradiation dose. Further investigations on standardized predation trials may lead to additional quality control tools for irradiated mosquitoes.