Investigating effects of environmental conditions on mosquito life cycle parameters is important considering that laboratory rearing protocols are usually not representative of the temperature, nutrition, and density fluctuations immature larval stages experience in the field. Generally, mosquitoes collected from the field are significantly smaller than those utilized in laboratory experiments, and studies have shown various other differences, including adult nutritional reserves [15, 16]. Several studies postulate that climate change may alter infectious disease dynamics, which is influenced by numerous vector and host factors [31, 32]. The abundance, distribution, and competence of disease vectors are of particular concern because they are easily influenced by climate and have the potential to impact human health through altered pathogen distribution . Most recently, outbreaks of arboviruses including CHIKV, RVFV, dengue and WNV have resurged or emerged in areas where they were previously undetected, suggesting a further increase in vector-borne disease [32–35].
Culex tarsalis is a particularly important species because they are found in a variety of habitats and are competent vectors for SLEV, WEEV and WNV [9, 11, 12, 36]. Seasonal and yearly fluctuations of Cx. tarsalis vector competence for WEEV and SLEV have been correlated with changing temperature in Kern County, California, indicating that climate change could facilitate the northward expansion of these viruses [28, 29, 31]. Our results indicate that larval rearing temperature had significant consequences on development, including shorter development time and smaller female body size as temperature increased. Similarly, other larval environment studies have revealed that temperature influences many Cx. tarsalis life history parameters, including decreased adult survivorship, adult body size, reproductive effort and immature development time, which was correlated with increasing temperature [14, 37]. Additional larval environment conditions have been examined with a variety of other mosquito species and revealed comparable trends [4, 23, 38, 39].
Many studies in Aedes mosquitoes have found that altering environmental parameters not only influences immature development, but also vector competence for arboviruses [5, 22, 24, 39]. We observed no consistent consequences of rearing temperature on the ability of Cx. tarsalis to become infected, disseminate or transmit WNV. Previously, it has been shown that changes in rearing conditions had no effect on the vector competence of Cx. annulirostris for MVEV, Cx. pipiens for RVFV or Cx. tarsalis for either SLEV or WEEV [18–20]. However, it is important to note that in our study, the abundance of adult mosquitoes was significantly affected by rearing temperature. There were significantly fewer adults emerging from the larval group reared at 31°C than at 19°C or 25°C in the majority of replicates, providing fewer mosquitos that are able to be infected and transmit virus. Though rearing temperature has no direct effect on vector competence, it has the potential to affect adult mosquito abundance and thus vectorial capacity, although this phenomenon will be influenced by density dependent regulation.