Correlated evolution between flight habit and diel activity in Coleoptera

Most beetles (Coleoptera) fly with their forewings (elytra) opened in front, with most of the lift being provided by the laterally orientated hindwings behind (four-winged fliers: 4WFs), but some beetles, such as flower chafers (Scarabaeidae: Cetoniinae), fly using only their hindwings while their elytra are nearly closed (two-winged fliers: 2WFs). Although 2WFs are reported to display greater flight ability than 4WFs, the adaptive significance of this type of flight is largely unknown. Herein, we tested if two-winged flight has evolved in relation to diurnality throughout Coleoptera. We found that two-winged flight has evolved several times throughout the order and that most 2WFs are diurnal. The correlation between two-winged flight and diurnality has also been supported by a phylogenetic comparative analysis in Scarabaeinae (dung beetles, Scarabaeidae). Two-winged flight is probably advantageous in escaping predation, reducing water loss from spiracles and blocking the heat of sunlight during the day.