Life cycle of Pontoscolex corethrurus (Müller, 1857) in tropical artificial soil

摘要

Pontoscolex corethrurus (Müller) is a widespread, peregrine earthworm species of the Glossoscolecidae family, native to the Neotropics. This endogeic earthworm shows wide tolerance to environmental variations, being found in many different habitats and soil types throughout the tropics and sub-tropics. To evaluate the life cycle of this species in tropical artificial soil (TAS), a substrate used in ecotoxicological tests, and the influence of food availability and humidity on its growth, earthworms were incubated individually under laboratory conditions. The life cycle was evaluated in four treatments with 24 earthworms (replicates) each: TAS (120. g) without additional food (TAS0), TAS with 5. g of horse manure (TAS5), TAS with 10. g of manure (TAS10) and TAS with 25% greater soil moisture with 5. g of manure (TAS5H). Food was provided every 14. d and the containers maintained at room temperature (20. ±4°C). Cocoons collected in the field were placed individually in the different treatments and the hatching date, growth, development, and reproduction followed for 50 weeks after hatching. New cocoons hatched at 34. d, adulthood was reached at 8 months, and cocoon deposition began 3 months later, so that its life cycle was completed in 12 months. By the 13th week all juveniles in TAS0 had died due to insufficient food resources, while in the other treatments, all the animals had matured by 44 weeks, with significantly higher biomass and length in TAS10 (0.72. g, 5.4. cm), compared with TAS5 and TAS5H (0.59-0.61. g, 5.1-5.4. cm). Growth and weight gain were positively related to food availability, and no negative effect of excess moisture was observed on their growth. With additional food TAS showed no limitations for the development of the species, and it can be used for ecotoxicological tests involving acute toxicity (mortality) and avoidance, although its potential use in chronic tests (reproduction) is more limited. The length of its life cycle and other biological characteristics associated with this parthenogenetic species create some challenges that must be dealt with before this species can be recommended for wider use as a standard ecotoxicological test species.