Abstract
Investigations were conducted during 1961-1965 on the dispersal of Nezara viridula in relation to feeding and oviposition. Adults of the hibernant generation feed and mate on the fields of rape, radish, wheat and barley, and then gravid females disperse to other kinds of host plants, e.g. potato, beans etc. for oviposition. This was supported by the low sex ratio observed on food plants after passing the date of 50 per cent mating.
During the early census period, the population density of adults in the potato field was very low and most of them were composed of females. Almost all the egg-masses were also deposited in this period. In addition, the mean duration of stay of these egg-laying females was considerably short in comparison with that of the adult migrants in the late period. It was considered that females of which ovaries had matured on the food plants flew into the potato field for oviposition and returned to the food plants soon after oviposition. Many adults of both sexes flew into the potato field in the late period principally for feeding and mating. The fact that an early stage of the host plant was availed by gravid females as an oviposition site and the same plant was accepted for feeding as it grew was maintained not only for potato but for paddy as well.
As stated above, it should be realized that what is meant by a polyphagous habit is not the non-selective preference to various host plants, but involves the sensitive preference to a particular host in an ideal state for the insect. In the study of polyphagous insects it is not only necessary to list many host plants available, but also to assess these host plants in relation to the life cycle and the behavior of the insect.
