Transgenic Aedes aegypti Mosquitoes Transfer Genes into a Natural Population.

In an attempt to control the mosquito-borne diseases yellow fever, dengue, chikungunya, and Zika fevers, a strain of transgenically modified Aedes aegypti mosquitoes containing a dominant lethal gene has been developed by a commercial company, Oxitec Ltd. If lethality is complete, releasing this strain should only reduce population size and not affect the genetics of the target populations. Approximately 450 thousand males of this strain were released each week for 27 months in Jacobina, Bahia, Brazil. We genotyped the release strain and the target Jacobina population before releases began for >21,000 single nucleotide polymorphisms (SNPs). Genetic sampling from the target population six, 12, and 27-30 months after releases commenced provides clear evidence that portions of the transgenic strain genome have been incorporated into the target population. Evidently, rare viable hybrid offspring between the release strain and the Jacobina population are sufficiently robust to be able to reproduce in nature. The release strain was developed using a strain originally from Cuba, then outcrossed to a Mexican population. Thus, Jacobina Ae. aegypti are now a mix of three populations. It is unclear how this may affect disease transmission or affect other efforts to control these dangerous vectors. These results highlight the importance of having in place a genetic monitoring program during such releases to detect un-anticipated outcomes.

Suppression of a Field Population of Aedes aegypti in Brazil by Sustained Release of Transgenic Male Mosquitoes.

The increasing burden of dengue, and the relative failure of traditional vector control programs highlight the need to develop new control methods. SIT using self-limiting genetic technology is one such promising method. A self-limiting strain of Aedes aegypti, OX513A, has already reached the stage of field evaluation. Sustained releases of OX513A Ae. aegypti males led to 80% suppression of a target wild Ae. aegypti population in the Cayman Islands in 2010. Here we describe sustained series of field releases of OX513A Ae. aegypti males in a suburb of Juazeiro, Bahia, Brazil. This study spanned over a year and reduced the local Ae. aegypti population by 95% (95% CI: 92.2%-97.5%) based on adult trap data and 81% (95% CI: 74.9-85.2%) based on ovitrap indices compared to the adjacent no-release control area. The mating competitiveness of the released males (0.031; 95% CI: 0.025-0.036) was similar to that estimated in the Cayman trials (0.059; 95% CI: 0.011-0.210), indicating that environmental and target-strain differences had little impact on the mating success of the OX513A males. We conclude that sustained release of OX513A males may be an effective and widely useful method for suppression of the key dengue vector Ae. aegypti. The observed level of suppression would likely be sufficient to prevent dengue epidemics in the locality tested and other areas with similar or lower transmission.

Field dispersal and survival of sterile medfly males aromatically treated with ginger root oil.

We studied the dispersal behavior and survival of sterile medfly males either treated or not with ginger root oil (GRO), in field conditions, in Petrolina-PE, northeast Brazil, from May 2006 to December 2007 in a sterile insect technique (SIT) program. The tsl strain Vienna 8 from the Ceratitis capitata Wied. (Diptera: Tephritidae), medfly, mass-rearing facility located in Juazeiro-BA, Brazil, was used. The results showed that sterile males either exposed or not to GRO exhibit similar dispersal behavior and postrelease survival. More than 60% of the sterile males, either treated or not treated with GRO, were recovered at a 25-m distance from the releasing point, approximately 20% at 50 m, and 5% in traps situated 100 m from the releasing point. Around 90% of the sterile males, exposed or not to GRO, were recovered 5 d after release of the sterile male individuals, whereas <1% were recovered after 11 d. Our results imply that ginger root oil can be used to treat sterile medfly males without interfering with their dispersal or survival in the field.