We propose to develop a novel and far-reaching field program that is initially concerned with aging and life span of Mediterranean fruit flies (medflies) in field populations in Greece and will later expand to include nematode worms. This will be the first research program concerned with aging in the field to use a laboratory model system for which a massive amount of baseline demographic data is available. The methodological concept for the program involves development of a new method for assessing the demographic characteristics of field populations that we refer to as the 'captive cohort method' and which relies on the information content of live-captured flies; that the post-capture patterns of reproduction and death will provide information about the age at capture and previous experience in the field. The approach will involve: (i) building upon the experimental and statistical methods developed in the highly successful program on the biodemography of the medfly; (ii)developing new statistical tools that can be brought to bear on the life history data collected on wild-caught medflies; and (iii)gathering baseline biodemographic information on the nematode, Caenorhabditis elegans, that will be used subsequently for expanding the system to include this well-studied invertebrate. We plan to use the approach to test hypotheses concerning the nature of aging, life span, gender differences, and feeding status of field populations. Our studies will provide insights into aging in the Wild that are impossible to obtain using any of the standard approaches in ecology for analyzing field mortality and aging including the use of mark-recapture techniques, individual tracking (e.g. radio collars), techniques for estimating an animal's age, and field cages. All of these conventional techniques have serious limitations regarding their ability to detect nuances in mortality and aging and/or to estimate age in older individuals. The proposed methods and the new assay technique will have broad applications and will thus provide opportunities for research on systems that heretofore were not amenable to field research on aging, particularly for studying aging in invertebrate populations.