Differences in male:female ratio among species of the genus Carabus L. (Coleoptera:Carabidae) in south Sweden

The male:female (sex) ratio is of considerable importance in understanding population dynamics of species. A null hypothesis was tested that the male:female (sex) ratio of Carabus species does not differ measurably when entire seasons are considered, but may differ considerably over shorter periods, indicating differences in annual rhythms between the sexes. The sex ratios in nine Carabus species (C. arvensis, C. cancellatus, C. coriaceus, C. glabratus, C. granulatus, C. hortensis, C. nemoralis, C. nitens, and C. violaceus) were studied using pitfall traps in forests and open land, totally 20 sites, during the entire seasons of 2007, 2009, and/or 2011. The ratio varied considerably and mostly consistently among species. The ratios were < 1 (usually ca 0.6), calculated over entire seasons in C. arvensis, C. glabratus and C. granulatus. On the contrary, males dominated in the other six species, and were particularly over-represented in C. cancellatus, C. nemoralis, and C. nitens with ratios of 2.2-2.7. Differences in the male:female ratio between different parts of seasons were demonstrated in three species. Calculated over entire seasons, there was some dominance of males in C. coriaceus and C. hortensis. Females dominated over males in July, males dominated in September. The pattern for C. violaceus was less consistent. The possible influence on the sex ratios of capturing method, habitat properties, nutritional status, season, differing life span and annual or diurnal rhythm of activity of males and females is considered and discussed.