Peristenus digoneutis Loan and Peristenus stygicus Loan, parasitoids of the European tarnished plant bug Lygus rugulipennis Poppius, are established in the United States for biological control of native North American Lygus species, and are being considered for deliberate release in Canada. High lifetime fecundity of parasitoids is considered a desirable attribute of biological control agents and therefore, an understanding of parasitoid reproductive biology is required. In the present study, the potential lifetime fecundity of both agents was compared under laboratory conditions to estimate the potential impact of Peristenus species on Lygus. Synovigenic P. digoneutis and P. stygicus females oviposited most actively in the first two weeks of their lifetime, with a maximum average daily oviposition rate after five days. The maximum number of eggs laid per day was 83 eggs for P. stygicus, and 36 eggs for P. digoneutis. P. digoneutis has an average potential lifetime fecundity of 385 [plus or minus] 35 SE eggs produced over 22 [plus or minus] 3 SE days. In contrast, P. stygicus females have a 50% higher mean potential lifetime fecundity reaching 782 [plus or minus] 65 SE eggs over 28 [plus or minus] 1 SE days. A positive correlation between lifetime fecundity and body size was found only for P. stygicus, and both species showed a significant relationship between lifetime fecundity and oviposition period. The present study demonstrates that the fecundity of P. digoneutis and P. stygicus is considerably higher than previously reported. Based on these findings, P. stygicus appears to be the most effective biological control agent for Lygus lineolaris (Palisot de Beauvois) when only fecundity is taken into consideration. [copyright] 2004 Elsevier Inc. All rights reserved. Peristenus digoneutis (Braconidae) : Parasite Peristenus stygicus (Braconidae) : Parasite Lygus (Miridae) : Host Animals and man; Control; Biological control; Reproduction; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Nearctic region; North America Lygus; Control by; Peristenus (Hymenoptera); Hymenopteran parasites; Reproductive biology of potential control agents; Peristenus digoneutis & Peristenus stygicus; Canada Peristenus digoneutis; Peristenus stygicus; Control of; Lygus (Hemiptera); Reproduction; Reproductive biology; Hemipteran hosts; Reproductive biology of potential control agents; Lygus; Canada none