Effects of light pollution on development rate of the painted lady butterfly (Lepidoptera: Nymphalidae)

Artificial light at night (ALAN) can disrupt circadian rhythms and phenology for lepidoptera since photoperiod is a dominant cue for their life cycles. The goal of this study was to discover how ALAN exposure affects the timing of caterpillar development into chrysalis and metamorphosis into a butterfly. The painted lady butterfly (Vanessa cardui) frequents Texas from spring through fall. For this project, commercially sourced V. cardui caterpillars were used to study effects of ALAN in controlled indoor conditions, at a constant temperature of 23 °C. Throughout October 2020, April 2021, October 2021, and March 2022, caterpillars were exposed to 0, 9.5, 17.5, or 24 h of 300 lux white light emitting diode (LED) lights, and the days until chrysalis formation and butterfly emergence were observed. The 17.5 and 24 h ALAN light cycles caused butterflies to emerge 1 to 3 days faster than 9.5 h exposure. V. cardui development was expected to be faster under blue versus orange LED lights as their photoreceptors are more sensitive to blue wavelengths. This was tested in July through September of 2022 with exposure to 24 h white, blue, or orange LEDs versus no ALAN. Orange LED exposed butterflies emerged a day or 2 slower than blue or white LED exposed ones. Studies in 2023 with 12 h ALAN from white, blue, or orange LEDs yielded similar results, and hemolymph melatonin was reduced by blue LED exposures. Therefore, orange ALAN seems to be less disruptive to V. cardui metamorphosis than blue or white ALAN.