Growth and reproduction of the slug Deroceras laeve (Müller) (Pulmonata: Stylommatophora) under controlled conditions

Abstract

The marsh slug Deroceras laeve (Müller) (Pulmonata: Stylommatophora) was recently introduced into the southeast of the Buenos Aires Province of Argentina, and has become one of the main pests of cropping systems under no-tillage management. The growth, survival, and reproduction of D. laeve were monitored at 12 deg C and 20 deg C to determine the most appropriate thermal conditions for its development. A sigmoid model (Y=A/(1+e**(B+Cx))) was used to describe the relationship between postembryonic development and temperature. At the beginning of development, the growth rate was lowest at 12 deg C but after the inflection point (21/2 months) was lower at 20 deg C than at 12 deg C. The slugs showed a higher mean body weight at 12 deg C (936.2 mg +/- SE 18.96) than at 20 deg C (409.4 mg +/- SE 16.02). Significant differences were seen in the mean incubation period at the different temperatures, as well as in the hatching rate, the duration of the preoviposition and oviposition periods, the number of eggs per clutch, and longevity; no differences were seen, however, in terms of mean fecundity. The incubation period was 35.3 and 16.03 days and the hatching rate 89.2% and 66.4% at 12 and 20 deg C respectively. At 20 deg C, longevity was less than half (21.9 weeks) that recorded at 12 deg C (54.4 weeks). At both temperatures the net reproductive rate (R sub(0)) was similar, but at 12 deg C the population increased 400 times in 33.1 weeks (T), while at 20 deg C it increased 359 times in half that time (T=16.5 weeks). These results show that, in the Buenos Aires Province, D. laeve produces two generations per year.