Wolbachia Infections in Aedes aegypti Differ Markedly in Their Response to Cyclical Heat Stress

Abstract

Aedes aegypti mosquitoes infected with Wolbachia bacteria are currently being released for arbovirus suppression around the world. Their potential to invade populations and persist will depend on interactions with environmental conditions, particularly as larvae are often exposed to fluctuating and extreme temperatures in the field. We reared Ae. aegypti larvae infected with different types of Wolbachia (wMel, wAlbB and wMelPop-CLA) under diurnal cyclical temperatures. Rearing wMel and wMelPop-CLA-infected larvae at 26–37°C reduced the expression of cytoplasmic incompatibility, a reproductive manipulation induced by Wolbachia. We also observed a sharp reduction in the density of Wolbachia in adults. Furthermore, the wMel and wMelPop-CLA infections were not transmitted to the next generation when mosquitoes were exposed to 26–37°C across all life stages. In contrast, the wAlbB infection was maintained at a high density, exhibited complete cytoplasmic incompatibility, and was transmitted from mother to offspring with a high fidelity under this temperature cycle. These findings have implications for the potential success of Wolbachia interventions across different environments and highlight the importance of temperature control in rearing.

An elusive endosymbiont: DoesWolbachiaoccur naturally inAedes aegypti?

“…Following removal, which may require multiple generations of treatment, the lack of infection can be confirmed through PCR or LAMP assays or by observing intracellular localization.This should be paired with a confirmation that the infection has persisted across generations in an untreated colony. Because Wolbachia infections may be heat(Ross, Wiwatanaratanabutr, et al, 2017) or antibiotic(Li et al, 2014) resistant, failure to eliminate Wolbachia does not necessarily confirm the lack of an active infection, so claims in this case should be supported by the other lines of evidence. The confirmation of natural Wolbachia infections in A. aegypti would open avenues for further research, including applications for disease control programs.…”

Metacommunity theory for transmission of heritable symbionts within insect communities

“…In some cases, insects have lost their endosymbionts completely following sufficiently strong heat-shock events (Thomas & Blanford, 2003). The sensitivity of bacterial symbionts to temperature suggests that the benefits and costs provided to hosts could be substantially altered in scenarios of significant environmental (Ross et al, 2017) and seasonal (Ferguson et al, 2018) change. These responses require further investigation, especially in the context of changing temperatures predicted to cause increased abiotic stress (Corbin et al, 2017).…”

“…Another potential application for metacommunity theory and insect-symbiont systems is to improve understanding of symbiont dynamics in scenarios where symbionts are being utilized for human benefit (Table 1, Scenario E). A prominent example is the use of Wolbachia to manipulate host sex ratios as a form of biocontrol against undesirable species (Hoffmann et al, 2015), particularly disease-spreading mosquitoes such as Aedes aegypti (Frentiu et al, 2014;Ross et al, 2017). One of the most important aspects for releasing Wolbachia-infected mosquitoes is knowing how they will disperse, both in terms of how the infected hosts will move and how the wild symbiotic communities will respond to Wolbachia introduction.…”

Variable Inhibition of Zika Virus Replication by Different Wolbachia Strains in Mosquito Cell Cultures

“…While some models predict successful control of arboviruses by Wolbachia strain wMel (6), concerns have been raised that over time, ongoing evolutionary adaptations of Wolbachia/vector/virus interactions may undermine the longterm effectiveness of wMel to control arboviruses (25). For example, recent studies suggest that wMel may struggle to integrate into large mosquito populations (26). This is due to a loss of maternal transmission and density and a reduced ability to induce cytoplasmic compatibility at tropical cyclic temperatures simulated in laboratory experiments (26).…”

“…For example, recent studies suggest that wMel may struggle to integrate into large mosquito populations (26). This is due to a loss of maternal transmission and density and a reduced ability to induce cytoplasmic compatibility at tropical cyclic temperatures simulated in laboratory experiments (26). As a result, strategies employing alternative Wolbachia strains, which effectively reduce viral titers without large host fitness costs, have been suggested to improve the efforts of a Wolbachia-mediated suppression strategy (27).…”