Attempt to Establish Field Colony of Culex restuans to Assess the Urban Heat Island Effect

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The Ohio State University

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The Urban Heat Island (UHI) effect explains why cities are typically warmer compared to surrounding suburban and rural areas. As mosquitoes are ectotherms, increases in temperatures can accelerate insect development, alter their phenology, and increase the disease incidence in urban settings. Culex restuans is a species of a mosquito commonly found in cities. Females of Cx. restuans transmit West Nile virus and enter a hibernation-like state, referred to as diapause, in response to short daylengths and low temperatures. Upon entering diapause, females cease reproductive development, stop blood feeding, and instead increase lipid accumulation, allowing them to survive without access to food during winter. Previous experiments have found that increases in temperature associated with the UHI effect during autumn inhibits diapause in a closely related species, Cx. pipiens. In this experiment, we hypothesized that high temperatures might also interfere with diapause initiation in Cx. restuans. To test this hypothesis, we attempted to establish a laboratory population of Cx. restuans. Oviposition traps were used to collect Culex egg rafts (F0) at three locations in central, Ohio, and larvae from the collected egg rafts were identified to species using morphology and PCR (polymerase chain reaction) assays. We then attempted to generate Cx. restuans F1 larvae to determine if temperatures that simulated the UHI effect in temperate biomes during winter months (20°C, 22°C, and 24°C) would inhibit diapause initiation. However, Cx. restuans that had emerged from field-collected rafts failed to successfully reproduce regardless of the presence of correct environmental cues and three different blood sources. Although we were unable to assess the impact of the UHI effect on diapause initiation in Cx. restuans, we found a high proportion of Cx. restuans within one urban site and a lower proportion within a rural site, as well as a high proportion of Cx. pipiens within a rural site. Difficulty establishing lab colonies of Cx. restuans limits our ability to study their physiology. Considering the importance of Cx. restuans for local disease transmission and their notable prevalence in urban settings, especially during early summer, further work is needed to develop successful techniques to establish and rear this medically important insect pest.