Seasonal preference of darkling beetles (Tenebrionidae) for shrub vegetation due to high temperatures, not predation or food availability

Abstract

Darkling beetles (Tenebrionidae) are ecologically important in many arid and semi-arid regions. Studies have shown that these beetles generally prefer vegetated microhabitats, but the specific reasons for this preference are not always clear. We deployed pit traps in shrub and unvegetated microhabitats, in late winter (cooler) and in late fall (hotter) during different years to determine if there were differences in beetle activity levels between microhabitats, and if these differences changed seasonally. We found significantly higher beetle activity levels in shrubs every year during the late fall, but no differences between microhabitats during the late winter. We also tethered 100 beetles of 5 species in these different microhabitats in late fall, to determine if predation risk differed between microhabitats. None of the tethered beetles were harmed. We also deployed pit traps in larger and smaller shrub patches in late winter, that differed significantly in plant litter density (food availability) but not temperature. We found no significant relationship between increasing patch size (food availability) and activity levels. These results suggest that tenebrionid beetles prefer shrubs during hotter times of the year, because shrubs provide them with refuges from extreme temperatures, not because of reduced predation risk or greater food availability.