GROWTH AND REPRODUCTION OF THE SLUG LIMAX VALENTIANUS FIRUSSAC IN EXPERIMENTAL CONDITIONS

Growth and reproduction of batches and isolated Limax valentianus Férussacslugs reared under long-day photoperiods were compared with thosereared under short-day photoperiods combined with higher temperaturesduring the dark period. Weight increase in L. valentianus occurredin three distinct phases: an initial phase of rapid growth (infantilephase), followed by a phase with a smaller increase in weight(juvenile phase) and finally a phase with minimal growth, duringwhich reproduction occurred (adult phase). This phase ended witha weight decrease, due to senescence. Short days associatedwith an increase in temperature during the night reduced thereproductive rate, but did not affect growth. Long days werefavourable for reproduction. Growth rate was fastest in isolatedindividuals reared under long days and warm nights, while reproductionwas greatest in isolated individuals reared under long daysand cool nights. Fertility generally decreased with age, butegg production of slug batches evolved through a maximum, occurringbefore mean life span. High slug density reduced reproductiverate and longevity. (Received 22 December 2000; accepted 10 October 2000)     

Daily activity rhythm and use of shelter in the slugs Deroceras reticulation and Arion distinctus under laboratory conditions

Daily activity of slugs, Deroceras reticulatum and Arion distinctus, was studied in the laboratory in relation to the presence of shelters so as to define optimal conditions for using traps to forecast crop damage. Under constant temperature and humidity, activity of slugs began with the lights off. Its arrest occurred after a period of activity with the lights on. Slugs rested most frequently under a shelter on bare earth and rarely used the same shelter for more than two consecutive days. When food was placed under the shelter, the number of slugs found under the shelter was more constant throughout the 24 h period, but lower during diurnal rest. The presence of 4% methiocarb pellets under the shelter led to an increased occupation by slugs, due to the poisoning of some of them. Acts of aggression were more numerous in A. distinctus than in D. reticulatum. In D. reticulatum the smallest slug was the least aggressive and suffered more attacks from the other slugs. In A. distinctus the numbers of attacks suffered or provoked varied little with the size of the slug, but the smallest slug showed less interactions with other slugs.     

Daily variation in the number of slugs under refuge traps

Daily variation in the number of slugs under and around 25 cm × 25 cm pad‐traps was recorded in plots of crop cultures. Grey field slugs Deroceras reticulatum and garden slugs (Arion distinctus and Arion hortensis) left traps at dusk and came back at the end of the night. The time of day at which the number of trapped slugs was maximal did not occur in the middle of the day, when slugs were inactive, but in the early morning and in the evening, a few hours before dusk. This was due to a rise in temperature under the traps in the middle of the day. However, the grey field slugs stayed under traps throughout the morning, when temperatures under the traps reached values more favourable for rest.     

FEEDING ACTIVITY OF LIMAX VALENTIANUS FERUSSAC: NOCTURNAL RHYTHM AND ALIMENTARY COMPETITION

Feeding activity of the slug Limax valentianus Férus-sacthroughout a 24-hour period began with the decrease in light.Feeding began 41 minutes after the start of locomotor activityand showed a maximum level in the beginning of the night L.valentianus had two to five meals each night, each meal lasting8.5 to 14 minutes. The overcrowding of the slugs induced a shorterduration of individual feeding periods and acts of aggressionduring meals. ^*Present address: Centre de Neurochimie, Laboratoire de neurobiologiemolécuiaire des interactions cellulaires. 5 rue BlaisePascal, 67084 Strasbourg, France (Received 7 July 1996; accepted 21 April 1997)