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Abstract
BackgroundA genetically-engineered strain of the dengue mosquito vector Aedes aegypti, designated OX3604C, was evaluated in large outdoor cage trials for its potential to improve dengue prevention efforts by inducing population suppression. OX3604C is engineered with a repressible genetic construct that causes a female-specific flightless phenotype. Wild-type females that mate with homozygous OX3604C males will not produce reproductive female offspring. Weekly introductions of OX3604C males eliminated all three targeted Ae. aegypti populations after 10–20 weeks in a previous laboratory cage experiment. As part of the phased, progressive evaluation of this technology, we carried out an assessment in large outdoor field enclosures in dengue endemic southern Mexico.Methodology/Principal FindingsOX3604C males were introduced weekly into field cages containing stable target populations, initially at 10∶1 ratios. Statistically significant target population decreases were detected in 4 of 5 treatment cages after 17 weeks, but none of the treatment populations were eliminated. Mating competitiveness experiments, carried out to explore the discrepancy between lab and field cage results revealed a maximum mating disadvantage of up 59.1% for OX3604C males, which accounted for a significant part of the 97% fitness cost predicted by a mathematical model to be necessary to produce the field cage results.Conclusions/SignificanceOur results indicate that OX3604C may not be effective in large-scale releases. A strain with the same transgene that is not encumbered by a large mating disadvantage, however, could have improved prospects for dengue prevention. Insights from large outdoor cage experiments may provide an important part of the progressive, stepwise evaluation of genetically-engineered mosquitoes.
Highlights
The recent worldwide increase in dengue [1,2] has made urgent the development and assessment of new tools for controlling the disease [3]
Results indicate that large outdoor cage experiments may provide valuable insights into the progressive, stepwise assessment of genetically-engineered mosquitoes
Pupae were sexed by visual examination for size at the field laboratory insectary using 3 ml plastic droppers and only adult males were added into treatment cages to avoid introducing the few females lacking the transgene (,0.5%) that could have interfered with population extinction
Summary
The recent worldwide increase in dengue [1,2] has made urgent the development and assessment of new tools for controlling the disease [3]. Concern regarding the use of GE organisms, and the absence of guidelines to help researchers interact with local communities, motivated the elaboration of a framework for the development, evaluation, and application of genetic strategies for prevention of mosquito-borne disease [16]. During Week 1 and 2 post-release, a total of 63 GDLS2 males from control cages and 50 OX3604C males that emerged from rearing trays at the field site were collected to compare size of the two strains. A genetically-engineered strain of the dengue mosquito vector Aedes aegypti, designated OX3604C, was evaluated in large outdoor cage trials for its potential to improve dengue prevention efforts by inducing population suppression. As part of the phased, progressive evaluation of this technology, we carried out an assessment in large outdoor field enclosures in dengue endemic southern Mexico
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