The biology, behaviour and control of the field slug, Deroceras reticulatum (Müller)
Deroceras reticulatum (Müller) is the most destructive slug pest of arable crops in Britain. Control on a field scale relies heavily on molluscicide pellets. These are often only partially effective; considerable economic loss and collateral damage still occur. More effective targeting of pellets will depend on accurate predictions of damage severity through a better understanding of population dynamics, reliable estimates of surface activity and behavioural studies to evaluate current control strategies. Lifecycle parameters of D. reticulatum were studied. There was considerable variation in growth even under identical conditions and growth rate was inversely related to survival. For field collected slugs, the association between growth rate and temperature was low but negative for spring hatching individuals; however, this was relatively trivial compared to the high and positive association exhibited by those hatching in autumn. For self-fertilised slugs, egg development took longer and the hatching rate was lower than for slugs laid by field collected adults, but the growth rate was faster. It is suggested that field populations may be composed of fast and slow growers, and that this might be determined by whether eggs are fertilised with auto- or allosperm. An equation was derived to predict female-phase maturity from body weight. Refuge traps sampled approximately one third of the surface active population over a 24 hour period. The timing and number of trap entries and exits did not differ between small and large D. reticulatum. Behavioural studies of D. reticulatum demonstrated that the time elapsed and distance travelled before feeding on bait pellets was shorter when they were broadcast compared to drilled. Soil splash did not reduce pellet efficacy. Trails were more sinuous on fine than coarse seedbeds and were reduced by pellets. The practical implications of these results for assessing and controlling D. reticulatum in arable crops are discussed.