Enhancing the scalability of Wolbachia-based vector-borne disease management: time and temperature limits for storage and transport of Wolbachia-infected Aedes aegypti eggs for field releases

Abstract

Background Introgression of the bacterial endosymbiont Wolbachia into Aedes aegypti populations is a biocontrol approach being used to reduce arbovirus transmission. This requires mass release of Wolbachia-infected mosquitoes. While releases have been conducted using a variety of techniques, egg releases, using water-soluble capsules containing mosquito eggs and larval food, offer an attractive method due to its potential to reduce onsite resource requirements. However, optimisation of this approach is required to ensure there is no detrimental impact on mosquito fitness and to promote successful Wolbachia introgression. Methods We determined the impact of storage time and temperature on wild-type (WT) and Wolbachia-infected (wMel or wAlbB strains) Ae. aegypti eggs. Eggs were stored inside capsules over 8 weeks at 18 °C or 22 °C and hatch rate, emergence rate and Wolbachia density were determined. We next examined egg quality and Wolbachia density after exposing eggs to 4–40 °C to determine how eggs may be impacted if exposed to extreme temperatures during shipment. Results Encapsulating eggs for 8 weeks did not negatively impact egg viability or resulting adult emergence and Wolbachia density compared to controls. When eggs were exposed to temperatures within 4–36 °C for 48 h, their viability and resulting adult Wolbachia density were maintained; however, both were significantly reduced when exposed to 40 °C. Conclusions We describe the time and temperature limits for maintaining viability of Wolbachia-infected Ae. aegypti eggs when encapsulated or exposed to extreme temperatures. These findings could improve the efficiency of mass releases by providing transport and storage constraints to ensure only high-quality material is utilised during field releases. Graphical Abstract

Dengue Exposure and Wolbachia wMel Strain Affects the Fertility of Quiescent Eggs of Aedes aegypti

“…Moreover, after a sharp decrease in Wolbachia density comparing the parental females to the adult females emerged from eggs stored for one week, we observed an increase in Wolbachia density in females as storage time increased. A more recent study assessing fitness of encapsulated eggs showed a relative maintenance of Wolbachia density across weeks of egg storage, with no detection of changes to fitness cost and egg viability over time [60]. Considering Ae.…”

Wolbachiaincompatible insect technique program optimization over large spatial scales using a process-based model of mosquito metapopulation dynamics

“…For example, the model can be used in the planning and optimization of new and existing Wolbachia IIT release programs in a variety of regions around the world, including those with subtropical and temperate climates with seasonal Aedes aegypti population fluctuations (Mores et al, 2020; Benitez et al, 2021). Additionally, the existing model can also be configured to study and optimize Wolbachia replacement programs where both adult male and female Wolbachia mosquitoes are released, or modified to model replacement programs where mosquitoes are released at different lifecycle points such as the egg stage (Allman et al, 2023).…”

“…Additionally, the existing model can also be configured to study and optimize Wolbachia replacement programs where both adult male and female Wolbachia mosquitoes are released, or modified to model replacement programs where mosquitoes are released at different lifecycle points such as the egg stage (Allman et al, 2023).…”