Comparison of oviposition and adult trapping to monitor wMel introgression for Wolbachia-based vector control

Wolbachia introgression into Aedes aegypti mosquito populations has been shown to be effective in preventing dengue and is being evaluated for WHO prequalification. Monitoring the long-term introgression of Wolbachia (wMel)-positive Aedes aegypti mosquitoes, however, requires labor-intensive and costly BG-Sentinel traps (BG-traps). More affordable alternatives, such as using oviposition traps (ovitraps), have not been fully evaluated. Ae. aegypti eggs and adults were collected from 124 ovitraps and 237 BG-traps, respectively, across 12 clusters in Belo Horizonte, Brazil from March to May 2023 as part of the EVITA Dengue trial. We used a qPCR assay to detect wMel in a sample of L3-L4 stage larvae (up to 29) that were reared from eggs in ovitraps and adults from BG-traps (up to 10 per BG-trap). We used mixed effects models to compare estimates of cluster-level wMel introgression from ovitrap and BG-trap data over time. Among 3,675 larvae reared from ovitraps, wMel prevalence was 0.50 (95% CI: 0.48-0.51). Among 1,244 adult Ae. aegypti tested from BG-traps, wMel prevalence was 0.45 (95% CI: 0.42-0.48). Cluster-level wMel introgression in larvae and adults was highly correlated (Spearmans r = 0.70, p = 6.71e-06). Multivariate analysis found that ovitrap estimates of introgression were associated with BG-trap estimates in the same month when models incorporated the previous months ovitrap wMel-positive count, the proportion of wMel in ovitraps in the current and previous month, and Ae. aegypti abundance. Leveraging this model, predicted wMel introgression from ovitrap data were highly correlated with observed introgression from BG-trap data (rs,counts=0.98, p=1.53e-14; rs,prevalences=0.82, p=0.11e-05) and provided greater precision than crude ovitrap-based estimates. These findings indicate that ovitrap-based monitoring represents a low cost, more efficient approach to evaluating introgression as the Wolbachia-based interventions are scaled up and implemented broadly in high burden regions for dengue and other arboviral diseases. Author SummaryDengue fever is a major global health burden, and one promising way to control it is by releasing Aedes aegypti mosquitoes infected with a bacteria called Wolbachia. This bacteria reduces the mosquitoes ability to spread dengue. However, monitoring the success of Wolbachia in mosquito populations over time requires expensive and labor-intensive traps. Our study explored a more affordable alternative: using oviposition traps (ovitraps), which collect mosquito eggs instead of adults. In Belo Horizonte, Brazil, we compared data from eggs collected in ovitraps with data from standard mosquito traps (BG-traps) that catch adult mosquitoes. By analyzing the mosquitoes for Wolbachia, we found that the egg-based method provided reliable estimates of Wolbachia levels in the mosquito population. These results suggest that ovitraps could be a cost-effective and efficient way to monitor Wolbachias spread. This approach could help improve dengue prevention efforts, making it easier for public health programs to track and expand this control strategy in areas where dengue is a major concern.