Butterfly behaviour under natural and artificial illumination conditions

Abstract

The behaviour and welfare of animals in captivity are of great importance to zoological collections, captive breeding programmes, food production, the pet industry, and more. Artificial lighting, as you may find in captivity, is commonly deficient in UV wavelengths, and could have significant impacts on the behaviour and welfare of taxa to which UV wavelengths are visible, such as birds, reptiles, and insects. While the effects of UV deficiency in lighting on captive vertebrate welfare have been studied, its implications for insect welfare remain largely unexplored. Here, I investigate the effect of UV-deficient light environments on the behaviour of Vanessa cardui, a butterfly that possesses a trichromatic visual system typical of many insect species commonly kept in captivity. In Chapter 3 butterfly activity behaviour under uniform UVpresent (+UV) or UV-absent (-UV) as well as in mixed heterogeneous lighting conditions (simultaneously +UV and –UV) was investigated. My study revealed that butterflies exhibit consistent activity behaviours including flying and alighted movement behaviours under homogeneous lighting conditions with either the presence or absence of UV light. However, in settings with both +UV and -UV areas, butterflies consistently exhibit a preference for areas with UV light, irrespective of overall brightness. In Chapter 4, I explored the innate colour preferences of butterflies for artificial flowers in a free-flight arena. Under +UV conditions, artificial flowers were preferred in the order blue>green>yellow>red, as suggested by the number of butterfly landing and probing behaviours. However, under –UV conditions the preferences for yellow and green were reversed, likely due to the differing visibility of UV reflectance features of these stimuli under the two illumination conditions. In Chapter 5, I explored the colour constancy and learning abilities of butterflies under the two lighting conditions. In environments lacking UV light, butterflies failed at learning a food association task related to a blue artificial flower stimulus, a task they readily learned under +UV conditions. This difference in learning performance can be attributed to the positioning of the blue-coloured stimuli within the Vanessa cardui colour space, particularly under –UV conditions. This interpretation finds further support by a second experiment where butterflies successfully learned the food association task to a yellow stimulus under –UV, indicating that it is not the light environment itself that hinders learning but rather the specific colour perception of stimuli within that light environment. These findings have significant implications for the current practices in captive insect enclosures and highlight the significance of UV light not only for butterflies but potentially for other insects as well. By enhancing lighting environments to include UV-rich illumination, captive butterfly houses can improve the activity levels and colour perception of butterflies, resulting in improved flying, foraging, and mating behaviours. This thesis concludes by recommending the inclusion of UV-enriched lighting in butterfly enclosures, alongside the use of UV-opaque filters on windows. This dual strategy aims to create a dynamic environment that encourages natural behaviours, enhances visual stimulus discriminability, and ultimately improves the welfare of captive-housed and bred butterflies.

Date of Award	2023
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Roger Santer (Supervisor) & Dylan Gwynn-Jones (Supervisor)