1. Adult feeding strongly increases longevity and fecundity in parasitic wasps. Searching for food resources involves costs; therefore, it is advantageous to be able to feed on the breeding substrate.
2. Cohorts of females of four drosophilid parasitoid species were assigned to different food treatments including starvation. Fat contents were measured and compared after 5 days. In this way the nutritional value of breeding substrates to females could be expressed in terms of energy reserves.
3. Three of the four species tested fed on natural breeding substrates. A fourth species did not produce evidence of such feeding. However, this species fed on honey when fat reserves were low.
4. Feeding is related to: (i) the species’ natural breeding substrate, (ii) the energy allocation and lifetime expectancy of the female, and (iii) time of the season.
5. Because feeding strongly influences longevity and fecundity, it is argued that the different feeding strategies found may affect competitive relationships between these drosophilid parasitoid species.