Comparison of the standard and boosted sterile insect techniques for the suppression of Aedes albopictus populations in semi-field conditions

Innovative control tools are needed against Aedes mosquitoes. The boosted sterile insect technique (SIT) consists of treating sterile males with a biocide prior to their release to contaminate larval habitats. We compared the efficacy of SIT and boosted SIT to prevent the emergence of adult Aedes albopictus in large cages. We used two ratios between sterile and fertile males: 5 (SIT5) or 1 (SIT1), boosted or not with pyriproxyfen (bSIT5 or bSIT1). The eggs were collected in ovitraps and the immature stages monitored until the emergence of adults or up to 15 days after hatching to estimate the logarithm of relative risk (log(RR)) of the emergence of adults relative to the control category. The concentration of pyriproxyfen in the ovitrap water did not change when sterile males were released with females or alone (χ2=0.99, df=1, P=0.547). This concentration was higher when the ratio between sterile and fertile males increased from 1 to 5: χ2=18.81, df=1, P=0.006. SIT1 was ineffective in suppressing mosquito populations: log(RR)=-0.24 [-0.86; 0.25] (95l% CI), and SIT5 was the most effective:-2.38 [-3.86;-1.4]. Boosted SIT was not as effective as SIT5. However, bSIT1 (-0.90 [-1.94;-0.25]) and bSIT5 (-0.65 [-1.43;-0.10]) were equally effective. Boosted males directly vectored pyriproxyfen to breeding sites. Boosted SIT was more effective than SIT alone with a low ratio between sterile and fertile males: it could be initially deployed to suppress the target population and then switched to standard SIT.