INFLUENCE OF LARVAE OF GASTROPHYSA-VIRIDULA ON THE DISTRIBUTION OF CONSPECIFIC ADULTS IN THE FIELD

1. Previous laboratory bioassays indicate that exocrine glandular secr etions of larvae of Gastrophysa viridula repel conspecific adults and deter them from feeding and oviposition. The present study was conduct ed to investigate the influence of larvae of G. viridula on conspecifi c adults in the field. 2. Within the G. viridula population studied, t wo generations were observed in a year. Occurrence of the different de velopmental stages overlapped temporally. 3. Some individual plants of Rumex obtusifolius, the host of the G. viridula population studied, g rew so close to each other that they were considered as a plant group. When investigating the spatial distribution of larvae and adults with in such plant groups, larvae were rarely found on plant groups on whic h adults were feeding. 4. A field experiment revealed that adults avoi ded plants of R. obtusifolius infested by conspecific larvae of the se cond and third instar. Adults still avoided these damaged plants when larvae had left them for pupation. 5. Gastrophysa viridula avoided ovi position on leaves and plants infested by conspecific larvae. Larvae o f the second instar significantly deterred oviposition when present at a high density (33.3 larvae/dm(2)), whereas larvae of the first insta r did not deter oviposition of conspecifics at either density tested, The oviposition deterring effect was also observed when just exocrine glandular secretion of larvae of the second instar was applied to the leaves in amounts equivalent to a density of 33.3 larvae/dm(2). 6. Ava ilability of food (R. obtusifolius) largely exceeded its exploitation in each group of plants examined. This may be due to either the spatia l separation of adults and larvae or the low population density observ ed an these plant groups.