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

Abstract

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 AE SE = 4.44 AE 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 AE 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 AE 0.72), and the OI ranged from 1 to 0.83 (0.095 AE 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.

What happens when we modify mosquitoes for disease prevention? A systematic review

“…Evidence to support these conclusions can be found when exploring recent important articles. We selected (non-systematically) 12 relevant articles published since March 2016 until now [22][23][24][25][26][27][28][29][30][31][32]. Critical successful evidence was reported, mainly field-based: (i) first stable transgenic CRISPR/cas9 aegypti-mosquitoes strain [23]; (ii) transgenic Anopheles population collapse in semifield using CRISPR/Cas9 [19]; (iii) near elimination of field mosquitoes after release of irradiated and Wolbachia-infected mosquitoes [24]; (iv) higher virus blockage of Wolbachia-infected fieldreared mosquitoes [25]; (v) wolbachia-mediated pathogen inhibition for ZIKV and ZIKV/DENV co-infection [26]; and (vi) released Wolbachia-aegypti stable over 12 months and 28 months at some sites, and reduced human dengue incidence [27,28].…”

“…Several studies suggested the need to release prohibitively large number of insects (100-102). To overcome that, two solutions were reported: releases in a ratio of 95% male mosquitoes (requiring a mass rear capacity) (11) or the introduction of insecticide resistance genes along with Wolbachia in the host insect, combined with a pre-release intervention to reduce (adult) insect vector numbers (29), (3). The unintended increase of the insect population after the release of the modified insects (reversal outcomes) was estimated by computational modelling studies (103), some of them based on field data of wMelPopaegypti (100) and of superinfected Aedes albopictus (93).…”

A comprehensive assessment of inbreeding and laboratory adaptation inAedes aegyptimosquitoes

“…Transgenic Ae. aegypti males possessing a dominant lethal system have been released in multiple locations where they have reduced population sizes, at least in the short term [6][7][8][9]. When these males mate with wild females, most offspring die before reaching the late pupal stage, though a low proportion can emerge as functional adults [10] and may persist for months after releases cease [9].…”

The Sterile Insect Technique (SIT) – an introduction

“…Garziera et al. () also presented data on a transgenic dipteran strain for SIT use, the well‐known disease vector mosquito Aedes aegypti (L.) (Diptera: Culicidae). They conclude that regular release is necessary for transgenic Ae.…”

“…This work is the first to present data on transgenic medflies, and clearly shows that more work is needed to fully assess their effectiveness under field conditions. Garziera et al (2017) also presented data on a transgenic dipteran strain for SIT use, the well-known disease vector mosquito Aedes aegypti (L.) (Diptera: Culicidae). They conclude that regular release is necessary for transgenic Ae.…”