Stenamma debile (Hymenoptera, Formicidae): Productivity and sex allocation across three years

Summary.

The numerical sex ratios of the facultatively polygynous ant Stenamma debile summed over several collecting sites in southern Germany were 255 males/gyne in 1997, 1.69 males/gyne in 1998 and 5.59 males/gyne in 1999. A large number of female sexuals were produced in queenless colonies, suggesting an inhibitive effect of queens on the production of gynes. Production of males and new workers varied little between the three study years. Production of sexuals plus workers covaried with queen number and worker number. Sex ratio was negatively associated with queen number and positively correlated with total sexual production. Between-year variation of sex ratios is probably correlated with differences in environmental conditions.¶Several mated young queens were found in colonies after the mating seasons in every year. Recruitment of queens was very low in the summer of 1997, and only two of 115 queens from 28 colonies appeared to be young, recently adopted queens. In contrast, 17 young and 59 older queens were collected from 26 colonies in fall 1999. Queen number thus increased by 28.8 % in 1999, but over all three years of 325 queens only 11.4 % were young queens. Incipient colonies with single queens were never observed. Colony structure and productivity of S. debile, as in other ants, apparently vary considerably over periods of several years. Census data from one particular year, and even from three consecutive years, were not sufficient to clarify the causes of variation in sex allocation.