Phenology, sex-ratio and protandry in three stag beetle species (Lucanidae) from central Italy

This study examines the annual activity patterns and variation in sex ratios across different months of the year for three Lucanidae species (Lucanus cervus, Lucanus tetraodon and Dorcus parallelipipedus) in three distinct regions of central Italy. The results reveal significant differences in the month-by-month activity patterns among the species, indicating that each species has its own unique activity pattern. Specifically, L. cervus shows activity from May to September, with the highest peak between 10 and 30 June. This species remains significantly active until the end of July. Lucanus tetraodon, on the other hand, exhibits activity from June to August, with a notable peak during the last 10 days of July. Dorcus parallelipipedus displays an extended activity phase, with peaks in the first 20 days of June and the middle of July. Interestingly, various individuals of this species were also observed in November, December and February. The prolonged activity pattern of D. parallelipipedus is primarily due to overwintering adults and overlapping generations. Both Lucanus species demonstrate clear protandry, where males dominate in the initial phase, followed by a more balanced sex ratio and even female dominance in the subsequent phase. In D. parallelipipedus, the trend in sex ratio is less apparent, likely because of overlapping generations and the survival of adults for 2-3 years. The different activity patterns observed between Lucanus species can be attributed to (1) their distinct geographical distributions, with one species better adapted to temperate climates and initiating activity earlier than the strictly Mediterranean species, and (2) a possible division of temporal niches to minimise reproductive interference, reducing the chances of interspecies encounters and cross-mating.