Trends in Parasitology
Volume 19, Issue 8, August 2003, Pages 349-355
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The first releases of transgenic mosquitoes: an argument for the sterile insect technique

https://doi.org/10.1016/S1471-4922(03)00144-2Get rights and content

Abstract

Potential applications for reducing transmission of mosquito-borne diseases by releasing genetically modified mosquitoes have been proposed, and mosquitoes are being created with such an application in mind in several laboratories. The use of the sterile insect technique (SIT) provides a safe programme in which production, release and mating competitiveness questions related to mass-reared genetically modified mosquitoes could be answered. It also provides a reversible effect that would be difficult to accomplish with gene introgression approaches. Could new technologies, including recombinant DNA techniques, have improved the success of previous mosquito releases? Criteria for an acceptable transgenic sterile mosquito are described, and the characteristics of radiation-induced sterility are compared with that of current transgenic approaches. We argue that SIT using transgenic material would provide an essentially safe and efficacious foundation for other possible approaches that are more ambitious.

Section snippets

Sterile insect technique

E.F. Knipling proposed the concept of releasing factory-produced sterile insects to control field populations of important pests 11, 12. The paradigm of this approach has been the successful elimination of the New World screwworm, Cochliomyia hominivorax, from the southern states of the USA, Mexico and all of Central America [13]. This area is now protected from re-invasion from South America by the release of relatively small numbers of sterile flies across a narrow barrier zone in Panama.

History of mosquito SIT

In a typical mosquito SIT programme, millions of males have been produced in a factory, sexually sterilized, and released into the field. These are intended to reduce wild populations by mating with virgin females who lay only sterile eggs. Large over-flooding ratios can be achieved by releasing sterile insects into seasonally or conventionally suppressed populations.

Mosquito releases have been performed for numerous purposes related to SIT (Table 1). Most of these were directed at answering a

First transgenics released must be sterile

The logical first step toward possible future release of fertile transgenic mosquitoes is to release material that is genetically sterile, so that the effects of the release could be reversed simply by termination. This approach would prevent vertical transmission of the transgene while enabling important parameters related to transgene behaviour to be assessed, thereby greatly reducing risk concerns. While it is possible that horizontal transmission of transgenes could occur by an unidentified

Transgenic technology and development of SIT

Given the limited success of SIT against mosquitoes, why should this technology be revived? Since the period when these releases were performed (1960–1980), several technologies have been developed that could improve the quality of released sterile insects and our ability to effectively release and monitor populations, such as: rapid DNA-based identification of members of species complexes; geographical information systems (GIS) and geographical positioning systems (GPS); remote-sensing

SIT before fertile transgenics

The most appropriate initial field evaluation of transgenic technology in mosquito control is the release of males that are separated from females via a transgenic sexing system and are radiation sterilized. Experience gained during a sterile release can provide essential safety and efficacy information, which will be required before considering release of fertile mosquitoes carrying sterility inducing factors, or refractory genes with or without a drive mechanism. The most likely outcomes are

Future perspective

Vector control is one of the few proven ways to reduce transmission of many vector-borne diseases. The effect on transmission is identical, regardless of whether the reduction is achieved by artificial means, such as residual spraying with DDT and cultural control, or by natural means, such as unfavorable seasonal climatic conditions or long-term climate change. The success of SIT can build directly upon these demonstrably effective measures.

Improvements to SIT have been made that could be

Acknowledgements

We thank Jorge Hendrichs, Gerald Franz and Chris Curtis for their comments on this article.

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