A Stimulus for Egg Production in Glossiphonia complanata (L.) (Hirudinoidea:Glossiphoniidae)

Laboratory-reared G. complanata cultured in changing water temperatures, which simulated those experienced in the field, produced eggs under a 12L/12D photoperiod, natural light conditions and continual darkness. In two regimes which incorporated accelerated 'field-temperature' changes and a natural photoperiod, egg-laying occurred only in the least accelerated regime. Leeches failed to mature at constant temperatures within the range 10.5 to 23°C under two separate photoperiods, viz. 12L/12D and natural light conditions. It is concluded that changing temperature conditions, perhaps a period of low temperatures followed by rising and higher temperatures, is an essential stimulus for egg production and that photoperiod is not involved.