Roksana Wilson
March 2023 | A dissertation submitted to the University of Bristol in accordance with the requirements for award of the degree of Doctor of Philosophy in the Faculty of Life Sciences, School of Biological Sciences
Abstract
The effects of night lighting on disease vectors have received increasing attention this last decade. Mosquitoes, midges, and sandflies are attracted to artificial light, and this could increase their contact with humans and facilitate disease transmission. Therefore, there is a pressing need for lights that are minimally attractive to nocturnal biting flies. In this thesis, I investigated the factors that drive light attraction in these insects and explored ways of reducing the attractiveness of ‘white’ light-emitting diodes (LEDs). First, I compared the attractiveness of five different colours of LED lamps (a broad-spectrum white, a 525 nm green, a 600 nm yellow, a 620 nm red, and a violet made by combining a 455 nm blue and a 640 nm red) in field experiments in Ghana. The white, yellow, green, violet, and red LEDs caught 50%, 24%, 12%, 8%, and 7% of the total Diptera respectively, and the white caught significantly more Diptera than the green, purple, and red LEDs. Second, I created three white LED lamps with different spectral compositions and used choice chamber assays on Culex pipiens mosquitoes to compare their attractiveness. Here I found that Red Green Blue (RGB) white light; made by combining 465 nm, 520 nm, and 625 nm LEDs; was significantly less attractive than broad-spectrum (BS) white light – attracting 44% of the mosquitoes. Furthermore, a Blue Yellow (BY) white light; made by combining 440 nm and 570 nm LEDs; was significantly more attractive than BS light – attracting 59% of the mosquitoes. Third, I tested these lights in the field in Scotland. The BY, BS, RGB, and no light (NL) control caught 37%, 27%, 24% and 13% of the total Diptera respectively. However, the only significant differences were between the NL control and the three lights.. Fourth, I carried out operant conditioning experiments on Culex quinquefasciatus mosquitoes, where a 465 nm blue or 520 nm green LED was paired with a sugar solution, to determine whether wavelength preferences were a result of colour vision. However, in these experiments, mosquitoes failed to associate the visual stimulus with the food source. My results show that light attraction in nocturnal biting flies is influenced by the wavelength composition of the light, and that increasing the proportion of long wavelength bands within a light may reduce its attractiveness.
…Spectral irradiance was measured using a NIST calibrated StellarNet radiometer with SpectraWiz software v5.33…
…Measurements of spectral irradiance (Figure 3.2A), spectral luminance (Figure 3.2B) and luminance (Figure 3.2C) were taken with a NIST calibrated StellarNet radiometer using SpectraWiz software v5.33…
…Luminance and irradiance (Chapter 3 Figure 3.2) were both measured using a NIST calibrated StellarNet radiometer with SpectraWiz software v5.33…
