Impact of Mosquito Age and Insecticide Exposure on Vector Competence of Aedes albopictus (Diptera: Culicidae) for Zika Virus

Abstract

Zika virus (ZIKV) can cause birth defects in humans and is a serious global public health concern. This arbovirus is primarily transmitted to humans by Aedes aegypti and Ae. albopictus mosquitoes; however, it can also be transmitted sexually and congenitally (from human to human). Vector-virus interactions influencing vector competence (the ability for a mosquito to become infected with and transmit a pathogen) vary and depend on biological (e.g., mosquito age) and environmental factors (e.g., temperature). A mosquito's chronological age at time of infection may impact its immune response against virus infection. There are no effective vaccines for most arboviruses, including ZIKV, hence insecticides are the best defense against mosquito transmitted ZIKV. Aedes albopictus is difficult to control due to its day-active nature and propensity to oviposit in containers throughout landscapes. However, residual barrier treatments can control Ae. albopictus and may use pyrethroid insecticides, such as bifenthrin. Since the efficacy of barrier spray treatments decreases over time due to environmental degradation, we characterized the extent to which sublethal bifenthrin exposure impacted vector competence for ZIKV. We exposed young (6-7 d post-emergence) and old (11-12 d post-emergence) Ae. albopictus to bifenthrin prior to oral exposure to blood meals containing ZIKV (7-day extrinsic incubation period). For this mosquito population, old mosquitoes experienced a significantly (P=0.0017) higher rate of mortality than young mosquitoes. Significantly (P=0.003) higher body titers were shown in old control group compared to young control group. Significantly (P=0.013, P=0.001) higher ZIKV dissemination rates and leg titers were observed in old bifenthrin-exposed mosquitoes compared to old control mosquitoes or young bifenthrin-exposed or control mosquitoes. This indicates that bifenthrin exposure may increase the potential for virus transmission (measured by proxy dissemination rate here); however, the degree of these impacts varies with mosquito age. Impacts of insecticides should be considered to improve risk assessments of potential vector populations.