The effects of genetic manipulation, dieldrin treatment and irradiation on the mating competitiveness of male Anopheles arabiensis in field cages.

Hanano Yamada,Jeremie Rl Gilles,Givemore Munhenga,Marc Jb Vreysen,David D Damiens

doi:10.1186/1475-2875-13-318

Abstract

BackgroundTo enable the release of only sterile male Anopheles arabiensis mosquitoes for the sterile insect technique, the genetic background of a wild-type strain was modified to create a genetic sexing strain ANO IPCL1 that was based on a dieldrin resistance mutation. Secondly, the eggs of ANO IPCL1 require treatment with dieldrin to allow complete elimination of female L1 larvae from the production line. Finally, male mosquito pupae need to be treated with an irradiation dose of 75 Gy for sterilization. The effects of these treatments on the competitiveness of male An. arabiensis were studied.MethodsThe competitiveness of ANO IPCL1 males that were treated either with irradiation or both dieldrin and irradiation, was compared with that of the wild-type strain (An. arabiensis Dongola) at a 1:1 ratio in 5.36 m3 semi-field cages located in a climate-controlled greenhouse. In addition, three irradiated: untreated male ratios were tested in semi-field cages (1:1, 5:1 and 10:1) and their competition for virgin wild-type females was assessed.ResultsThe ANO IPCL1 males were equally competitive as the wild-type males in this semi-field setting. The ANO IPCL1 males irradiated at 75 Gy were approximately half as competitive as the unirradiated wild-type males. ANO IPCL1 males that had been treated with dieldrin as eggs, and irradiated with 75 Gy as pupae were slightly more competitive than males that were only irradiated. Ratios of 1:1, 5:1 and 10:1 irradiated ANO IPCL1 males: untreated wild-type males resulted in 31, 66 and 81% induced sterility in the female cage population, respectively.ConclusionsAn irradiation dose of 75 Gy reduced the competitiveness of male ANO IPCL1 significantly and will need to be compensated by releasing higher numbers of sterile males in the field. However, the dieldrin treatment used to eliminate females appears to have an unexpected radioprotectant effect, however the mechanism is not understood. A sterile to wild-type ratio of 10:1 effectively reduced the population’s fertility under the experimental field cage conditions, but further studies in the field will be needed to confirm the efficiency of sterile ANO IPCL1 males when competing against wild males for wild females.

Highlights

To enable the release of only sterile male Anopheles arabiensis mosquitoes for the sterile insect technique, the genetic background of a wild-type strain was modified to create a genetic sexing strain ANO IPCL1 that was based on a dieldrin resistance mutation
Male An. arabiensis males destined for release in programmes that include a sterile insect technique (SIT) component, need to endure several treatments: (1) for the purpose of sex separation, a complex translocation of the Rdl gene was induced for the development of the genetic sexing strain (GSS) ANO IPCL1 [7]; (2) dieldrin treatments at immature stages are necessary for female elimination from the production line; and, (3) irradiation at pupal stage is required for the sterilization of the males prior to release
The results indicate that prohibitive reductions on competitiveness due to biological effects of the presence of the Rdl gene, and the complex translocation associated with this GSS can be precluded as the competitiveness of the ANO Insect Pest Control Laboratory (IPCL) males was not compromised when competing with wild-type males for wild-type females in a field-cage setting

Summary

Introduction

To enable the release of only sterile male Anopheles arabiensis mosquitoes for the sterile insect technique, the genetic background of a wild-type strain was modified to create a genetic sexing strain ANO IPCL1 that was based on a dieldrin resistance mutation. The competitiveness of colony reared, sterilized, and released male mosquitoes is linked to numerous biological parameters, such as longevity, flight performance, spatial occupation of the habitat, available sperm complement, and mating behaviour [2,3,4,5]. Each of these parameters could be influenced by the various steps of the production process of the sterile males, three of which in particular (in addition to the rearing process and laboratory colonization [6]) may induce a significant decline in overall quality of the An. arabiensis males. The male pupae are subjected to a dose of 75 Gy of gamma or X-ray irradiation resulting in >98% sterility [8] before they emerge and are ready for release

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Conclusion