The effect of host deprivation and egg expenditure on egg load, realized fecundity, and parasitism of the ichneumonid Mastrus ridihundus, a gregarious parasitoid introduced for the control of codling moth in California, were investigated under laboratory conditions. Females deprived of hosts had a greater egg load than females provided with excess hosts and no egg resorption was observed, the results even suggesting that females continue to add reserves to eggs over time. Host-deprived females were able to immediately use the eggs stored in their ovarioles, even after 6 days of host deprivation, and egg laying peaked on the first day of host availability. However, beyond the first day of reproduction, both daily oviposition and host attack rates were reduced, and overall, host-deprived females had a lower lifetime fecundity and attacked a lower number of hosts compared to females that were provided with excess host since their emergence. The occurrence of a potential trade-off between early and late reproduction and between reproduction and survival was also investigated. Early oviposition did not affect future reproduction nor survival. These results are discussed in the context classical biological control, with the view to understand how to manipulate host availability during the prerelease period to increase the reproductive potential, and therefore the fitness and establishment potential of M. ridibundus. [copyright] 2005 Elsevier Inc. All rights reserved. Cydia pomonella (Tortricidae) : Host Mastrus ridibundus (Ichneumonidae) : Parasite Animals and man; Control; Biological control; Reproduction; Reproductive behaviour; Reproductive productivity; Life cycle and development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Cydia pomonella; Control by; Mastrus ridibundus (Hymenoptera); Hymenopteran parasites; Parasitoid reproductive capacity; effect of host deprivation & egg expenditure; control significance; Mastrus ridibundus Mastrus ridibundus; Control of; Cydia pomonella (Lepidoptera); Egg laying; Egg number; Life cycle; Life history tradeoffs; Lepidopteran hosts; Parasitoid reproductive capacity; effect of host deprivation & egg expenditure; control significance; Cydia pomonella none