Biology of some Diplopoda, with special reference to Cylindroiulus punctatus

Abstract

Cylindroiulus punctatus, Polydesmus angustus and Tachypodoiulus niger are the common millipedes of deciduous woodland floor. Of the three species, C. punctatus is specially interesting, since it spends part of its life cycle in leaf litter and part inside the bark of rotten logs. Eggs are laid below the bark and the following three instars also live here. The fourth instars leave the bark and go into litter: here they moult three times togive fifth, sixth and seventh instars. The seventh instars undergo development either in litter or beneath the bark of logs. They moult to give the eighth instars which in females all become sexually mature, although they continue to moult afterwards. The males cease to moult at eighth instar after attaining sexual maturity. Two peaks occur in the activity of C. punctatus in litter, one in spring and the other in autumn. The first peak occurs at the time of the migration of the adults from the litter into the bark for oviposition, and the second peak when the adults migrate back from the logs into the litter.In the field, the whole life cycle is completed in about three years, but in the laboratory at a constant temperature of 23[degrees]C., and under constant darkness, the life cycle is completed in about two years. Laboratory and field observations show that this species does not show any special preference for leaf or bark of any deciduous tree, as long as they are sufficiently rotten. Distribution of the species is regulated by the availability of the oviposition sites, food and humid surroundings. Polydesmus angustus is also found in wooded areas rich in decomposing litter. It shows only one peak of activity during its breeding period. The life cycle of P. angustus is more simple than C. punctatus, and is completed in the nature in about 12-14 months. In the laboratory at a constant temperature of 23[degrees]C., the life cycle is completed much earlier. It does not migrate into the logs for oviposition, instead it constructs nests on the ground in which eggs are deposited.P. angustus also feeds on the rotten leaves of anydeciduous tree, and diet has considerable effects on the duration of its life cycle and the size of the adults.Tachypodoiulus niger has a wider range of distribution and food preference than either of the two species. It is found both in grassland and in areas rich in decomposing vegetation. It also shows a single peak of activity.