Growth and reproduction of the slug Limax valentianus Férussac in experimental conditions

Abstract

Growth and reproduction of batches and isolated Limax valentianus Férussac slugs reared under long-day photoperiods were compared with those reared under short-day photoperiods combined with higher temperatures during the dark period. Weight increase in L. valentianus occurred in three distinct phases: an initial phase of rapid growth (infantile phase), followed by a phase with a smaller increase in weight (juvenile phase) and finally a phase with minimal growth, during which reproduction occurred (adult phase). This phase ended with a weight decrease, due to senescence. Short days associated with an increase in temperature during the night reduced the reproductive rate, but did not affect growth. Long days were favourable for reproduction. Growth rate was fastest in isolated individuals reared under long days and warm nights, while reproduction was greatest in isolated individuals reared under long days and cool nights. Fertility generally decreased with age, but egg production of slug batches evolved through a maximum, occurring before mean life span. High slug density reduced reproductive rate and longevity.