Diurnal and Sex Ratio Flight Activity of Rare Cavity-Dweller Eucnemis capucina Ahrens, 1812 (Coleoptera: Eucnemidae) in Lowland Deciduous Forest: Case Study from Czech Republic

The cavity-dwelling saproxylic beetles are very poorly studied because of their hidden way of life, and they are threatened by forest management. Eucnemis capucina is a rare and sporadic species in all of its distribution area. This species is associated with old hollow trees, which may be why it is on the red lists of many European countries; however, this association could be an indicator of diverse forest structure. We monitored diurnal and seasonal flight activity with intercept flight traps installed on massive ash trees during three seasons. The observed peak of seasonal activity was in May and June. Contrasting most eucnemids, E. capucina is clearly a daytime species, with flight activity between 8:00 and 20:00 and peaking at 14:20. The peak of flight activity is the same for both sexes, but males are more active at the beginning and end of the flight period compared to females. An unequal sex ratio 1.91:1 (F:M) of captured individuals was recorded. The increasing body size of females affected the number of eggs in the body of adult females. The average potential fecundity of a female was 54 eggs, 10 eggs per 1 mm of female body length. The eggs themselves were oval in shape and only the length of the eggs correlated to the body size of the females; the width did not change with body size and did not correlate with egg length, either. We also confirmed that even a single hollow tree can host high numbers or whole populations of rare species and, thus, have a high conservation value. Our study may help better understand the biology of cavity-dwelling beetles and their active life.