Activity patterns of Cybotus estriatus (LeConte, 1878) (Coleoptera: Tenebrionidae) on a Caribbean beach

Abstract

Sandy beach ecosystems are extreme environments in which darkling beetles (Tenebrionidae) have been usually reported as a dominant component of the fauna. The abundance and richness of tenebrionids in arid zones is facilitated by specific physiological, morphological, and behavioural traits, such as limited activity patterns or the use of suitable microhabitats. Activity patterns of tenebrionid beetles have been investigated mainly in large-size species, but the response of small species remains basically unknown. Considering this, we developed a study in a Caribbean beach in Costa Rica with the aim of identifying daily activity patterns of Cybotus estriatus (LeConte, 1878), a darkling beetle of 2–3 mm in length relatively frequent in the circum-Caribbean beaches. In addition, we assessed how vegetation cover influences the abundance of this small tenebrionid species. Observations were performed between 7:00 h to 18:30 h, within a range of temperatures from 28°C to 47°C. Cybotus estriatus exhibits a bimodal activity pattern similar to those observed for other tenebrionids. It remains active at a temperature range of 35°C to 44°C, but shows a higher activity around 10:00 h and 15:30 h, at temperatures between 38°C and 42°C. We also found a strong dependence of C. estriatus on beach vegetation, providing the first data on the effect of vegetation cover in small tropical beetles inhabiting sand beaches. Our results suggest that body size may not be the critical factor determining activity in tenebrionids, and that preserving the natural vegetation in sandy beaches is essential to maintain the biodiversity of these ecosystems.