Effect of interruption of over-flooding releases of transgenic mosquitoes over wild population of Aedes aegypti: two case studies in Brazil

The number of mosquito populations resistant to insecticides is increasing along with the reemerging of vector-borne diseases. New technologies are under evaluation to complement the strategies used against these mosquitoes. Transgenic mosquitoes are one approach that some countries are considering and they are being evaluated to control the wild population. Although they have achieved success in population suppression of Aedes aegypti (L.) (Diptera: Culicidae), these studies have not demonstrated what the outcomes are when releases are interrupted (ceased). In this study, after demonstrating suppression of Ae. aegypti using transgenic technology, changes in the spatial distribution of the infestation and the abundance of the vector Ae. aegypti were assessed in the post-release period, along with fluctuation of transgenic mosquitoes in two areas of Brazil. In both pilot trials, there was an average suppression of ca. 70% of the wild population due to the release of transgenic males compared to the pre-release period. In Juazeiro (Mandacaru), in the post-release phase, the number of eggs per trap ranged between 0.06 and 14.41 (mean ± SE = 4.44 ± 0.44), and the ovitrap index (OI = number of ovitraps with eggs/total number of ovitraps recovered) ranged from 0.01 to 0.43 (0.13 ± 0.01). In Jacobina (Pedra Branca), during the post-release phase, the number of eggs per trap ranged between 1 and 7.2 (1.72 ± 0.72), and the OI ranged from 1 to 0.83 (0.095 ± 0.032). The mosquito population in Juazeiro (Mandacaru) remained suppressed for 17 weeks after the release interruption, whereas in Jacobina (Pedra Branca) suppression lasted 32 weeks. In Juazeiro, transgenic larvae were detected up to 5 months after the interruption of the over-flooding releases of transgenic males. In Jacobina, they were found up to 2 months after the release interruption. The number of eggs collected increased 4-5 months after the release interruption, which indicated that the Ae. aegypti population had been re-established after the interruption of releases. The results demonstrate that the technique requires a continuous release in the treated areas, and after suppression, the release rate can be decreased and used as a barrier against external migration.