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

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