The introduction of the Wolbachia bacterium into Aedes aegypti mosquito populations is a promising biocontrol strategy aimed at reducing the transmission of arboviruses. This approach often involves the mass release of Wolbachia-infected mosquitoes. Egg releases using water-soluble capsules containing mosquito eggs and larval food offer a potentially attractive method for scaling up these efforts by reducing on-site resource requirements.

However, it is crucial to optimise this approach to ensure no detrimental impact on mosquito fitness and to promote successful Wolbachia introgression. This publication addresses critical aspects of optimising egg release strategies by investigating the time and temperature limits for storage and transport of Wolbachia-infected Aedes aegypti eggs.

Executive Summary:

This study investigated the impact of storage time and temperature on the viability and Wolbachia density of encapsulated and unencapsulated Aedes aegypti eggs infected with either the wMel or wAlbB strains. The researchers stored eggs inside capsules for up to 8 weeks at 18 °C or 22 °C and assessed hatch rate, emergence rate, and Wolbachia density. Additionally, they examined the effects of exposing unencapsulated eggs to extreme temperatures (4–40 °C) for 48 hours to simulate potential conditions during shipment. The key findings include:

• Encapsulation of eggs for 8 weeks did not negatively impact egg viability, adult emergence, or Wolbachia density compared to unencapsulated controls stored at 22 °C.
• Storing encapsulated wMel-infected eggs at 18 °C did not significantly improve egg fitness compared to storage at 22 °C.
• Exposure of unencapsulated eggs to low temperatures (4–36 °C) for 48 hours generally maintained egg viability and resulting adult Wolbachia density. However, wMel density showed a statistically significant decrease at 4 °C, with two instances of wMel loss observed out of 160 samples.
• Exposure of unencapsulated eggs to 40 °C for 48 hours significantly reduced both egg viability and Wolbachia density in both wMel and wAlbB strains, with near-complete Wolbachia loss observed in the majority of emerged adults.

The study concluded that it has defined critical time and temperature limits for maintaining the viability of Wolbachia-infected Ae. aegypti eggs during storage and potential transport. These findings can significantly improve the efficiency of mass release programmes by providing crucial constraints for ensuring the use of only high-quality material in the field.

Further Information:

• Authors: Megan J. Allman, Ya‑Hsun Lin, D. Albert Joubert, Jessica Addley‑Cook, Maria Camila Mejía‑Torres, Cameron P. Simmons, Heather A. Flores, and Johanna E. Fraser.
• Journal: Parasites & Vectors (2023) 16:108.
• DOI: https://doi.org/10.1186/s13071-023-05724-1.
• Funding: This research was supported by funding from the Australian Government Research Training Program (RTP) Scholarship.