Biology and individual growth of Milax gagates (Draparnaud, 1801) (Pulmonata: Stylommatophora)

In the southeast of Buenos Aires Province, Argentina, Milax gagates (Draparnaud, 1801) causes reductions in yields of soybean, sunflower and oilseed rape under no tillage by damaging seeds and seedlings. Whilst there are some studies of the damage caused by M. gagates to sunflower and soybean crops, and the control of slugs in soybean, there is little information on the biology and ecology of this species of slug. The aim of the present study was to analyze the biology and individual body growth of M. gagates. The study was carried out at 20 degrees C and a 16/8 h light/dark regime. The egg stage took about 23 days (SD = 2.7 days) and viability was 75.4%. The slugs reached maximum fecundity between the 19th to 29th week with values of 4 and 9 eggs/slug/week, respectively. The net reproductive rate varied considerably among cohorts, 7.2 to 33.2, but the generation time was similar, 181 to 206 days. The growth pattern was well described by the three parameter logistic model. The slugs reach half of their maximum weight at about 150 days old (inflection point of the growth curve), 22 to 43 days before the start of oviposition. The maximum mean body weight of the adult slugs was 2149.6 mg, but in the population maximum body weight varied between 991.2 mg to 3308.0 mg (+/- 2x579.2 mg) among slugs. The biological parameters and individual growth of M. gagates from Argentina were consistent with that of an annual reproductive cycle of a semelparous species.