K. 2005. Effects of food stress and density in different life stages on reproduction in a butterfly. Á/ Oikos 111: 514 Á/524.Availability of adequate nutrition and (rearing) density are among the most important factors affecting growth, development and reproduction in animals. In holometabolous insects diets and energetic needs change between life stages, with storing of larval resources, adult feeding and reproduction being linked strategies. Nevertheless, studies investigating nutritional (and density) effects across metamorphic boundaries are largely lacking. We aim at disentangling the functional basis of reproductive patterns by independently manipulating larval and adult (1) density and (2) access to food, respectively, in the tropical butterfly, Bicyclus anynana . (1) A high larval rearing density had, contrary to common wisdom, very little impact on body size, but reduced larval development time through increased growth rates. The latter is thought to be an adaptation to high densities, driven by the risk of larval food resources becoming exhausted before reaching metamorphosis. Larval density and male company during oviposition (i.e. adult density) had no detectable effects on female reproduction. (2) Larval food stress prolonged larval development time and reduced larval growth rate, body size, fecundity and reproductive investment. Detrimental effects on female reproduction were mediated through a reduction in body size. Additional negative effects of adult food stress on fecundity were largely confined to females being fed as larvae ad libitum, while those being previously starved showed reduced performance regardless of adult income. Effects on egg size were inconsistent and, overall, marginal. Our results show that restricted food access in different developmental stages may set different limits to reproduction, either posed by shortage of larval-derived storage reserves (i.e. nitrogenous compounds) or adult income (i.e. carbohydrates). Thus, one should be cautious when stating that one or the other type of nutrients is ultimately limiting to reproduction. Rather, our findings highlight the importance of resource congruence and of considering both, larval-and adult-derived resources for reproduction.The pattern of resource allocation has critical consequences for individual fitness and is fundamental to numerous fields of research in behavioural, evolutionary and population ecology. In particular the availability of adequate nutrition comprises one of the most important factors affecting growth, development and reproduction in animals. Food shortage during juvenile development was repeatedly found to increase development time, and to decrease growth rates, body size and reproductive output later in live (Briegel 1990, Berrigan and Charnov 1994, Blanckenhorn 1998, Fischer and Fiedler 2001a. Likewise, limited food access in the adult stage was found to diminish performance in various ways (Boggs and Ross 1993, Braby and Jones 1995, Fischer and Fiedler 2001b. Among the most obvious effects are those on...