Effect of Egg Irradiation on Development and Sterility of Wild-Type and Wolbachia Trans-Infected Aedes aegypti Mosquito Vectors
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Background
Sterile Insect Technique (SIT), Incompatible Insect Technique (IIT) and a combination become the alternative promising vector control approaches. In these approaches, the targeted mosquitoes need to be sterilized and released. So far, the irradiation of mosquitoes has been conducted at the pupae or adult stages. In this study, we investigated the possibility of the X-ray irradiation at the egg stage and also assessed the effect on the development and sterility of both wild-type and Wolbachia trans-infected Aedes aegypti mosquito vectors.
Methodology/Principal Findings
The eggs of Aedes aegypti , both wild-type and Wolbachia trans-infected lines, were irradiated using X-ray at the doses of 1, 3, 5 and 7 Gy. Development of immature stages was observed. For wild-type Aedes aegypti , X-ray irradiation at the doses from 3 Gy decreased the development of the first instar larvae and increased the development of the third instar larvae but there was no effect on pupae when compared to those of the controls ( p < 0.05). For Wolbachia trans-infected ones, the irradiation dose as low as 1 Gy could increase the development of the forth-instar larvae while the irradiation dose of 7 Gy induced significantly high mortality in pupae. To assess sterility, males and females emerged from irradiated eggs were mated with the normal ones. Results showed that the irradiation doses for sterilization of Wolbachia trans-infected Ae. aegypti was lower than those of the wild-type ones. The egg hatch rate of both males and females could significantly be reduced from the irradiation dose of 5 Gy in Wolbachia trans-infected Ae. aegypti and 7 Gy in the wild-type ones.
Conclusions/Significance
Our findings revealed the possibility to sterilize both wild-type and Wolbachia trans-infected Ae. aegypti by applying a low-dose X-ray irradiation at the egg stage. Egg irradiation could make an implementation of SIT, IIT or combined IIT/SIT for vector control much more feasible as the sterile dry eggs are easier to distribute and operate when compared to other developmental stages of mosquitoes.
Author summary
Releasing sterile males to control Aedes aegypti mosquitoes and the diseases they transmit is one of the alternative environmental friendly approaches. So far, sterilization of mosquitoes has been targeted on the pupae or adult stages. In this study, we investigated the possibility to apply X-ray irradiation at the egg stage which is more feasible and easier to operate. Aedes aegypti eggs, both infected and uninfected with the Wolbachia bacteria, were irradiated by X-ray at the doses of 1, 3, 5 and 7 Gy. Results showed that the irradiation dose of 7 Gy significantly caused more than 92% sterility in both wild-type males and females. However, this irradiation dose could be reduced to 5 Gy to sterilize both males and females infected with Wolbachia . In conclusion, the X-ray irradiation dose of 5 Gy could be an optimum dose for irradiation of Wolbachia -infected Ae. aegypti eggs as it could induce high level of sterility in males and nearly complete sterility in females while the irradiation dose of 7 Gy could induce sterility in both males and females uninfected with Wolbachia . This approach should be useful for the sterile male release programs to control Aedes -transmitted diseases.
