DAILY ACTIVITY RHYTHM AND USE OF SHELTER IN THE SLUGS DEROCERAS-RETICULATUM AND ARION DISTINCTUS UNDER LABORATORY CONDITIONS

Daily activity of slugs, Deroceras reticulatum and Arion distinctus, w as studied in the laboratory in relation to the presence of shelters s o as to define optimal conditions for using traps to forecast crop dam age. Under constant temperature and humidity, activity of slugs began with the lights off. Its arrest occurred after a period of activity wi th 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 foun d 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 poiso ning of some of them. Acts of aggression were more numerous in A. dist inctus 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 li ttle with the size of the slug, but the smallest slug showed less inte ractions with other slugs.