Variability in oviposition by workers of six species of Myrmica (Hymenoptera, Formicidae)

Abstract

Oviposition by workers of 6 species from genus Myrmica - M. rubra, M. ruginodis, M. sabuleti, M. scabrinodis, M. schencki and M. sulcinodis - was compared under a variety of laboratory conditions. Experiments were initiated using freshly overwintered, queenless cultures of workers i.e., at the start of a second summer of adult life. Some cultures (c 30 workers) of all six species accumulated eggs; most contained an embryo which could develop into a male but usually a few were sterile trophic eggs. The presence of overwintered 3rd instar larvae had no effect upon the numbers of eggs. For each species, the frequency distributions of the numbers of eggs laid per culture were highly overdispersed with many accumulating no eggs and a few culture many eggs. Despite the intraspecific variation, interspecific differences were statistically significant - M. ruginodis and M. schencki laid the most eggs and M. sabuleti the fewest. Generally oviposition rates were greatest during the first 3 weeks following hibernation and thereafter, eggs were laid intermittently until the next winter period. Workers of all species oviposited in their third summer of life following a second laboratory winter and showed similar initial per capita egg-production to that of the previous year. M. ruginodis and M. schencki lived longer than other species (which all died before the third winter) and had some workers which survived another winter and laid eggs in their fourth summer. No relationship could be detected between the propensity for worker oviposition in the 6 species, and other characteristics such as worker size, average level of polygyny in the species or its taxonomic position.