Investigating the Effects of Male Size and Pronotal Glowspots on Female Courtship Behaviour of the Glowspot Cockroach (Lucihormetica verrucosa)

Lucihormetica verrucosa (Blattodea, Blaberidae) are highly sexually dimorphic cockroaches, with the males having two symmetrically organised ‘glowspots’ on their pronotum. The spots can range in colour from whitish-yellow to red, depending on the quantity of carotenoids in their diet. These spots auto-fluoresce when exposed to UV wavelengths, with the amount of fluorescence inversely related to the carotenoid content. The diet-dependent aspect of the pronotal spots insinuates that they are a fitness-dependent trait and thus inform sexual selection, but existing studies have not directly investigated the role of the pronotal spots in courtship behaviour. Invertebrate sexual selection is commonly informed by male size, with females selecting for smaller males. Small male size can have less cost towards females and may help males in competition for mates. This study looked at whether female courtship behaviour is influenced by (1) mass of the males or (2) the presence/absence of the male pronotal spots. It was found that (1) the mass of the males did not significantly affect the frequency of female courtship behaviours. However, (2) the presence of the male pronotal spots did significantly affect the frequency of female interactive behaviours (those where the female directly interacts with the male), including antennal feeling, mounting, and touching body-to-body. The results suggest that (1) the mass of males does not inform female mate choice but (2) females do consider the male pronotal spots.