THE EFFECT OF THE LENGTH OF LARVAL DIAPAUSE ON CASTE DETERMINATION INTHE ANT MYRMICA-RUBRA

Larvae of Myrmica rubra can develop into queens only if they have pass ed through a period of halted development called diapause. These 'quee n-potential' larvae develop from eggs laid during the early summer tha t reach a mass of at least 1mg by the 3(rd) instar stage in the autumn . Development then ceases and normally restarts only after chilling fo r a minimum of three weeks. The larvae then develop into queens or wor kers depending, among other things, on their treatment by the workers. In this paper we show that the period of diapause can be extended by prolonged cold temperature treatment and that this extension of diapau se increases the production of queen pupae but not worker pupae. The e xtended diapause may allow a greater number of larvae to develop more fully their wing and ovariole buds before pupation. These results sugg est that the duration of cold winter temperatures may have a significa nt bearing on colony demography and sex-allocation ratios.