Abstract
Clitellate specimens of Pontoscolex corethrurus were used to study their growth and reproduction in the soils of different age groups of rubber plantations. Pontoscolex corethrurus was selected for the present study because of the following factors: (i) It had high biomass and density values in rubber plantations. (ii) Recognized to be widely tolerant to environmental factors. (iii) Possesses continuous breeding strategy with high fecundity and high hatching success of cocoons. Peak of biomass of Pontoscolex corethrurus appeared on the 30th day both in unutilized land soil (790mg) and 14yr old Hevea soil (680mg), while the biomass peaks in 20yr old (680mg) and 25yr old (730mg) Hevea soils appeared 15 days later i.e. on the 45th day. Rate of growth of the earthworms was significantly higher (p< 0.05) in the unutilized land soil (13mg worm-1day-1), compared to that in 14yr old(9mg worm -1day-1 ), 20yr old (6mg worm-1day-1) and 25yr old (7mg worm-1 day-1) Hevea soils. The general growth rate of the studied worm in different substrate followed the order: Unutilized land soil > 14yr old Hevea soil > 25yr old Hevea soil > 20yr old Hevea soil. Total number of cocoon produced by Pontoscolex corethrurus within 60 days in the soils of different age groups of Hevea plantations and unutilized land differed. It was highest in the 14yr old Hevea plantation (44 cocoons) and lowest in the unutilized land soil (24 cocoons) at the end of experiment. Among the different substrates, highest and lowest rate of reproduction of Pontoscolex corethrurus were recorded in the 20yr old Hevea soil (0.51 cocoon worm-1week-1) and unutilized land soil (0.28cocoonworm-1day-1) respectively. The rate of fecundity in different substrates maintained the following order: 20yr old Hevea soil > 25yr old Hevea soil > 14yr old Hevea soil > Unutilized land soil. Hatching success (%) of the cocoons in different substrates was as follows: 25yr old Hevea soil > 14yr old Hevea soil > 20yr old Hevea soil > Unutilized land soil Steady increase in growth and production of cocoons in Pontoscolex corethrurus in mineral soils without any food additives indicates that this worm is exclusively geophagous or endogeic type of earthworm.
Key words: Rubber plantation, mineral soil, Pontoscolex corethrurus, growth, reproduction
