Ovitraps Provide a Reliable Estimate of Wolbachia Frequency during wMelBr Strain Deployment in a Geographically Isolated Aedes aegypti Population

Abstract

Deployment of Aedes aegypti mosquitoes carrying the endosymbiont bacterium Wolbachia has been identified as a promising strategy to reduce dengue, chikungunya, and Zika transmission. We investigated whether sampling larvae from ovitraps can provide reliable estimates on Wolbachia frequency during releases, as compared to the expensive adult-based BG-Sentinel. We conducted pilot releases in a semi-field system (SFS) divided into six cages of 21 m2, each with five ovitraps. Five treatments were chosen to represent different points of a hypothetical invasion curve: 10%, 25%, 50%, 75%, and 90% of Wolbachia frequency. Collected eggs were counted and hatched, and the individuals from a net sample of 27% of larvae per treatment were screened for Wolbachia presence by RT-qPCR. Ovitrap positioning had no effect on egg hatching rate. Treatment strongly affected the number of eggs collected and also the hatching rate, especially when Wolbachia was at a 10% frequency. A second observation was done during the release of Wolbachia in Rio under a population replacement approach when bacterium frequency was estimated using 30 BG-Sentinel traps and 45 ovitraps simultaneously. By individually screening 35% (N = 3904) of larvae collected by RT-qPCR, we were able to produce a similar invasion curve to the one observed when all adults were individually screened. If sampling is reduced to 20%, monitoring Wolbachia frequency with 45 ovitraps would be roughly half the cost of screening all adult mosquitoes captured by 30 BG-Sentinels. Our findings support the scale-up of Wolbachia releases, especially in areas with limited resources to afford massive trapping with BG-Sentinel traps.

High throughput estimates of Wolbachia, Zika and chikungunya infection in Aedes aegypti by near-infrared spectroscopy to improve arbovirus surveillance

“…Each agarose gel electrophoresis reaction contained a Wolbachia positive control (mosquitoes from a lab colony whose infection has been confirmed by PCR), a PCR-confirmed negative control, and a blank sample (distilled water). Extraction and PCR protocols were performed following published materials 20 , 27 , 29 . The PCR data was used as the gold standard, i.e., a mosquito that received an infected blood meal with a negative PCR result, was considered negative.…”

“…For example, whether to increase or reduce the number of insects in future releases or even stop the release if a desired frequency has been achieved. Traditionally, adult mosquito trapping is carried out with BG-Sentinel traps, but ovitraps are sometimes used concomitantly, usually on a weekly basis 26 , 27 , 29 . Collected samples (adult mosquitoes or eggs allowed to hatch in an entomological lab) are often screened with quantitative polymerase chain reaction (qPCR) technique to check for the presence of Wolbachia , but arboviruses presence in Wolbachia -infected and wild A. aegypti is rarely assessed 27 .…”

Optimising the surveillance of Aedes aegypti in Brazil by selecting smaller representative areas within an endemic city

“…In such places, the most productive breeding sites are plant dishes, domestic drains and roof gutters. Although those differences in containers productivity, both areas have similar infestation as measured by the House Index [12, 14, 57, 58]. It means that public health managers from cities with high urban heterogeneity like Rio de Janeiro must be more careful in selecting smaller representative areas and consider other parameters than we did at Foz do Iguaçu.…”

Aedes aegypti oviposition‐sites choice under semi‐field conditions

“…Oviposition assays were conducted in outdoor field cages at Fundação Oswaldo Cruz campus, Rio de Janeiro, Brazil (de Jesus et al, 2020). The main experimental protocol consisted of distributing a range of potential oviposition containers filled with water throughout each field cage, as shown in Figure 1 and Table 1 for Experiment 1.…”

“…aegypti generally deposit eggs on damp surfaces just above the waterline, such as the inner surfaces of discarded containers (Christophers, 1960 ; Clements, 1992 ; Cunha et al, 2002 ; David et al, 2021 ; de Abreu et al, 2015 ; Longdon et al, 2015 ; Maciel‐de‐Freitas, Marques, Peres, Cunha, & de Oliveira, 2007 ). In addition, this species engages in a behaviour known as ‘skip oviposition’, which means that a single female can distribute eggs from a single batch across several oviposition containers (Colton et al, 2003 ; de Abreu et al, 2015 ; de Jesus et al, 2020 ). These characteristics are likely to enhance the survival rate of the immature stages in this species by reducing intraspecific competition and avoiding exposing all offspring to abiotic stresses, breeding site drying and exposure to insecticides (Reiter, 2007 ).…”