Comparative Studies on the Population Dynamics of Important Lepidopterous Pests on Cabbage

The author made observations on the distribution of larvae and pupae of Pieris rapae crucivora, Mamestra brassicae and Autographa nigrisigna on each individual plant of cabbage. Young larvae of all the three species distributed mainly on the underside of leaves of intermediate ages. Characteristic distribution for each species was observed after middle instars of larvae: Pieris larvae a migrated toward the upper side of young leaves with their growth and went back again toward the underside of leaves of lower part before pupation. Mamestra larvae showed a migrating tendency toward the upper young leaves with the progress of age and always stayed on the underside of leaves. Almost all of the fifth and sixth (last)-instar larvae aggregated at the head of the plants, whereas full-grown larvae went down into the soil for pupation. Autographa maintained a sessile habit throughout the larval life, so the later instar larvae and also the pupae were found on the underside of old leaves of lower part. Tht effect of larval density on the vertical distribution was observed only in Mamestra; the aggregating tendency of the later instar larvae was accelerated by the increase of density. Each species distributed on the plant irrespective of the existence of other species and also of the seasons.