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Abstract
Mosquito-borne diseases present some of the greatest health challenges faced by the world today. In many cases, existing control measures are compromised by insecticide resistance, pathogen tolerance to drugs and the lack of effective vaccines. In light of these difficulties, new genetic tools for disease control programmes, based on the deployment of genetically modified mosquitoes, are seen as having great promise. Transgenic strains may be used to control disease transmission either by suppressing vector populations or by replacing susceptible with refractory genotypes. In practice, the fitness of the transgenic strain relative to natural mosquitoes will be a critical determinant of success. We previously described a transgenic strain of Anopheles gambiae expressing the Vida3 peptide into the female midgut following a blood-meal, which exhibited significant protection against malaria parasites. Here, we investigated the fitness of this strain relative to non-transgenic controls through comparisons of various life history traits. Experiments were designed, as far as possible, to equalize genetic backgrounds and heterogeneity such that fitness comparisons focussed on the presence and expression of the transgene cassette. We also employed reciprocal crosses to identify any fitness disturbance associated with inheritance of the transgene from either the male or female parent. We found no evidence that the presence or expression of the effector transgene or associated fluorescence markers caused any significant fitness cost in relation to larval mortality, pupal sex ratio, fecundity, hatch rate or longevity of blood-fed females. In fact, fecundity was increased in transgenic strains. We did, however, observe some fitness disturbances associated with the route of inheritance of the transgene. Maternal inheritance delayed male pupation whilst paternal inheritance increased adult longevity for both males and unfed females. Overall, in comparison to controls, there was no evidence of significant fitness costs associated with the presence or expression of transgenes in this strain.
Highlights
Mosquito species are important global vectors of diseases such as malaria, dengue, yellow fever, filariasis and encephalitis
For such technology to become a viable part of an integrated pest management programme, genetically modified mosquitoes must be able to compete successfully for available resources. This requires either the absence of a fitness load associated with the genetic modification, or else a modest fitness load that may require the use of a gene drive mechanism to help fix the transgene in the population [12,13]. To achieve this outcome it is important that transgenic mosquitoes, destined for mass rearing and field release, have minimal fitness costs associated with transformation and transgene expression
The hemizygous strains were established from reciprocal crosses between KIL and EVida3 homozygotes such that the transgene was inherited from either the paternal (EV3P) or the maternal (EV3M) parent
Summary
Mosquito species are important global vectors of diseases such as malaria, dengue, yellow fever, filariasis and encephalitis. As with any genetic intervention, the ultimate goal of disease control through transgenic technology will rely upon effective inheritance of the transgene and its introgression into field populations For such technology to become a viable part of an integrated pest management programme, genetically modified mosquitoes must be able to compete successfully for available resources. This requires either the absence of a fitness load associated with the genetic modification, or else a modest fitness load that may require the use of a gene drive mechanism to help fix the transgene in the population [12,13]. To achieve this outcome it is important that transgenic mosquitoes, destined for mass rearing and field release, have minimal fitness costs associated with transformation and transgene expression
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