This reports on continuing investigations of prey-predator interactions in long-lived ecosystems comprising self-perpetuating populations of the moth Anagasta kuehniella (Zeller) and its pathogen, the larva-infecting Bacillus thuringiensis Berliner; its predator, the egg-feeding mite Blattisocius tarsalis (Berlese); and its endoparasite, the larva-feeding wasp Devorgilla canescens (Gravenhorst). Invasions by a predator, the flour beetle Tribolium confusum Jacquelin du Val, are analyzed. These Anagasta ecosystems demonstrate the basic regulatory mechanisms of any self-perpetuating population wherever located. These ecosystems have demonstrated that the maintenance of balance between a host and its parasite is either nonreciprocal or reciprocal, a differentiation that is determined by the degree to which the host is fortuitously protected from parasitization. When a natural enemy population is in reciprocal balance with that of its prey, regulating the population density of both its prey and itself, the food supply of the prey automatically becomes for the prey an unlimited resource. This occurs in the Anagasta ecosystems despite the fact that the strictly limited amount of food is replaced, whether wholly used or not, according to certain schedules. As in nature the abundance of an established animal population (the relative numbers of individuals in an area) is an expression of (1) the distribution of favorable habitats (disposition of individuals or groups over an area), and (2) the population saturation levels of such habitats (the full occupancy of a locality as determined by environmental resistance to population reproductivity).