A Mark-Release-Recapture Experiment with Radio-Sterilised Aedes Albopictus Males As Part of a Sterile Insect Technique Programme Against the Vector Mosquito in Panchvati, Mauritius

The survival and dispersal of radio-sterilised Aedes albopictus males were investigated during two mark-release-recapture trials (MRR1 and MRR2) in Panchvati, a village in Mauritius. Laboratoryreared males were irradiated at 40 Gy, marked with fluorescent powder, released in the village centre and subsequently recaptured on days three, four, five and six post-release. Overall recapture rates during MRR1 and MRR2 were 0.8 and 1.3 %, respectively, while 64.3 and 82.1 % of the total males recaptured were collected within a radius of 40 m from the release point. Average life expectancy of the released males was 9 days in both MRR trials. Based on our results, in order to achieve an adequate coverage of sterile males in Panchvati during a sterile release programme, males should be released on a weekly basis with distance between release stations not exceeding 80 m. Moreover, although MRR1 and MRR2 were conducted during winter, an important population of wild Ae. albopictus males were estimated in Panchvati, 2246 (95 % CI: 1260–3232) and 4095 (95 % CI: 3358–4831) males/ha, respectively. Reducing the species incidence using conventional control methods is therefore very important before the start of a sterile release programme in Panchvati. Nevertheless, based on the male population estimate obtained during MRR1 (conducted in July when Ae. albopictus incidence is naturally at its lowest), and with the aim of achieving a sterile/wild males ratio of 10:1, approximately 20 000 sterile males/ha would need to be released on a weekly basis in Panchvati to significantly reduce the vector population. The control of Aedes albopictus (Diptera: Culicidae) is a national priority in Mauritius since the mosquito is a vector of Chikungunya and Dengue viruses in the country (Beesoon et al. 2008; Ramchurn et al. 2009; Issack et al. 2010). To efficiently plan a sterile release programme against Ae. albopictus, it is crucial to understand the ecology and behaviour of the released males in the target area (Lacroix et al. 2009). Information that can be obtained during a mark-release-recapture (MRR) study releasing male mosquitoes include the survival, dispersal and behaviour of the latter in the field (Bellini et al. 2010) as well as an estimation of size of the wild male population in the area based on the proportion of released and wild males collected (Gouagna et al. 2015). Data on population size estimates are equally important since it helps determine the number of sterilised males to be released in order to achieve an effective sterile to wild male release ratio (Jeffery et al. 2009). Very little information is currently available on male mosquito ecology, and even less on radiosterilised Ae. albopictus males in the field. In Mauritius, Panchvati (20°04’60”S 57°41’30”E), a small (3 ha) rural village, was selected as a pilot site to investigate the Sterile Insect Technique (SIT) against Ae. albopictus (Iyaloo et al. 2014). SIT, in this case, basically involves an inundation of the village with radio-sterilised males that can potentially lead to the biological suppression of its wild population (Knipling 1955). As an initial part of the programme 3848 and 2200 laboratoryreared, radio-sterilised (irradiated at 40 Gy using a cesium-137 irradiator; Gammacell 1000, Nordion International Inc., Ontario, Canada), marked (dusted with fluorescent pigment) Ae. albopictus males were released as 3-day-old adults in the village centre during two MRR trials (MRR1 and MRR2) on 25 July 2015 and 21 May 2016, respectively. Generations F27 and F35 of an insecticide-susceptible strain of Ae. albopictus originating from Pointe des Lascars (a village 1.2 km away from Panchvati) were used in this study. Released males were recaptured at 28 collection