Tis But a Scratch! Negligible fitness costs of AalDV2 infection in Aedes albopictus under fluctuating temperatures and implications for viral biocontrol

Abstract

Aedes albopictus is a major arboviral vector whose global expansion, driven by human activities and climate change, poses a growing public health concern for a number of neglected tropical diseases in both tropical and temperate regions. As a poikilotherm, its biology and population dynamics are strongly influenced by temperature, thereby shaping disease transmission. To thwart and control its geographic expansion, effective vector control strategies are increasingly critical. Densoviruses (DVs), such as AalDV2, are being explored as mosquito viral biocontrol agents due to their restricted host range and ability to disseminate through oviposition sites. However, the influence of environmental parameters on the interactions between Ae. albopictus and AalDV2 remains poorly understood. This makes their performance under realistic, fluctuating thermal regimes difficult to estimate. In this study, we investigated the combined effects of temperature and AalDV2 exposure on Ae. albopictus survival and development across its full life cycle. Mosquitoes were reared under fluctuating temperature regimes (26-28{degrees}C and 32-34{degrees}C, 12:12 day-night cycles) and exposed to AalDV2 or a control treatment. Chronic exposure to 32-34{degrees}C significantly reduced overall survival, decreasing median lifespan by approximately 10 days (HR=2.21, p=0.0018), with a deleterious effect increasing over time. It extended aquatic lifespan and increased pupal mortality. It also reduced adult lifespan in both sexes with a stronger effect in females. AalDV2 exposure had no significant effect on overall survival, stage-specific mortality, or adult lifespan. However, a significant interaction between viral exposure and thermal stress was detected on aquatic lifespan: AalDV2-exposed females showed further extended larval and pupal development specifically under the 32-34{degrees}C regime, without any effect on survival. These results indicate that the biocontrol potential of AalDV2 cannot be assessed independently of thermal context: while lethal effects were absent under both fluctuating regimes, the prolongation of aquatic development by the virus under thermal stress may have indirect consequences for mosquito population dynamics that warrant further investigation. Author SummaryThe tiger mosquito Aedes albopictus is among the most invasive species worldwide including in temperate areas and a major vector of dengue, chikungunya, and Zika viruses. Concerns with this species are growing in the context of climate change and effective vector control strategies are increasingly critical. Densoviruses, such as AalDV2, are small DNA viruses that infect mosquitoes and are being explored as potential biocontrol agents because of their restricted host range and ability to spread through shared breeding sites and kill mosquito aquatic stages. However, the understanding of influence of the environmental conditions such as temperature on the effectiveness of these viruses remains incomplete. Here, we investigated the combined effects of fluctuating temperatures (26-28{degrees}C and 32-34{degrees}C day/night cycles) and AalDV2 exposure on mosquitoes throughout their entire lifespan, from larva to adult death. Our results show that chronic exposure to high fluctuating temperatures strongly reduces mosquito survival, mainly by increasing mortality during pupation and shortening adult lifespan. While AalDV2 exposure did not significantly affect survival or mortality under either temperature regime, a significant interaction between viral exposure and thermal stress was detected: AalDV2-exposed females showed prolonged aquatic development specifically under the high temperature regime (32-34{degrees}C). This result demonstrates that temperature shapes the outcome of host-virus interactions even in the absence of lethal effects, and that realistic thermal variability must be incorporated into the evaluation of densovirus-based biocontrol strategies.