Seasonal dynamics and emergence pattern of a tropical earthworm,Drawida calebi(Oligochaeta)

Abstract

271Cocoon morphology (shape, size, colour and ornamentation), hatching, and seasonal dynamics of cocoon and juveniles of D. calebi have been studied in an Indian pasture site. The average live weight of cocoon is 15.17 mg, length/diameter 0.94, and moisture content 72.5 go/o. Just-hatched juveniles weigh on an average 10.4 mg, and are 10.5-17.5 mm in length. The incubation period lasts 56.33 ± 2 days during November-December in laboratory cultures (25°C, and moisture 15 g%). A maximum of 64.0 live cocoons/m 2 with a live weight of 0.971 g/m 2 were deposited during October-November 1977, but very few during summer months. A surface-living species, D. ca/ebi shows single peak emergence pattern in December-January. It is estimated that 78 cocoons (live and dead)/ m 2 (780,000/hectare), were produced in the field by D. calebi population in a year . Thus the total cocoon production is 11.83 kg/hectare/year. It is estimated that 3 cocoons/individual/year are produced by D. calebi in field conditions.

Population biology and reproductive strategy ofDichogaster bolaui (Oligochaeta: Octochaetidae) in two tropical agroecosystems

“…During each sampling, 5 random samples were taken from an area of 25 x 25 x 20 em separately from each study site (Snedecor and Cocharane 1967;Dash and Senapati 1980). Earlier works of Dash and Patra (1977), Senapati et al (1979), Dash and Senapati (1980) and Senapati andDash (1981, 1983) on tropical earthworms from various agroecosystems had standardised methods for sampling, collection, preservation and analysis of cocoons and worms. D. bolaui was dominant in both number and biomass (> 80%) in both the study sites.…”

“…The climate is broadly divided into 3 seasons: winter (OctoberFebruary), summer (March-mid June) and rainy (mid June-September). Climatological parameters have been measured by standard methods (Senapati et al 1979;Dash and Senapati 1980;Senapati andDash 1981, 1983). Comparative characteristics of both the study sites relating to physical, chemical and biological parameters have been given in table 1.…”

“…Because of discontinuity and unstability, vertical pyramidal structure is not very much distinct. Studies on the horizontal and vertical distribution of earthworms have been made by Dowdy (1944), Gerard (1967), Bouche (1972), Rundgren (1975), Dash and Patra (1977), Senapati et al (1979), Dash and Senapati (1980) and Sahu and Senapati (1986). Stratification to upper 10em of soil depth along with single population peak in the pasture and two population peaks in the compost pit showed that D. bolaui is a surface living earthworm.…”

“…Among the species of earthworms whose reproductive biology and life cycle have been worked out are Eisenia foetida (Savigny), Allolobophora longa, Ude, A. caliginosa (Savigny), Lumbricus terrestris, Linnaeus, L. rubellus, Hoffmeister, Bimastos zetek(Smith and Gittins), Eudrilus euginiae (Kinberg), Milsonia anomala, Omedo, Drawida calebi Gates, D. willsi, Michaelsen, Lampito mauritti Kinberg and Ochtochaetona surensis (Michon 1954;Avel 1959;Murchie 1960;Satchell 1967;lavelle 1977, 1978Hartenstein et al 1979;Senapati et al 1979;Dash and Senapati 1980;Senapati 1980;Pani 1986). Discontinuous mode of reproduction has been advocated for surface living earthworms (Satchell 1967;Rundgren 1977;Dash and Senapati 1980).…”

“…A comprehensive programme for understanding the environmental regulation of life cycle strategy in tropical earthworms has been taken up in different agroecosystems. Dash and Patra (1977), Senapati et al (1979), Dash and Senapati (1980) and Sahu and Senapati (1986) have reported the activity of earthworms in lowland, upland and plain pasture ecosystems of Orissa. Impact of large herbivore grazing and thermohydric stress on tropical earthworms has been studied by Senapati and Dash (1981, 1983, 1984.…”