none Praon pequodorum Viereck parasitized the pea aphid (PA), Acyrthosiphon pisum (Harris), and the blue alfalfa aphid (BAA), A. kondoi Shinji. There were preferences for aphids of certain ages but no significant preference for either species. Parasitism significantly affected reproduction of both BAA and PA. Aphids parasitized at 1-5 days old (at 20 degree C), produced significantly fewer offspring than unparasitized aphids up to 9 days of age. PA exposed to the parasitoid at 6 days of age did not show significant reproductive reduction until they were 13 days old. All aphids parasitized at less than or equal to 4 days old failed to reproduce. Apterous BAA, parasitized when 5 days old, reproduced when reaching adulthood but apterous PA did not. Parasitized alate BAA or PA did not reproduce regardless of age when parasitized. Biometrics; Reproduction; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships Praon pequodorum (Braconidae); Hemipteran hosts; Acyrthosiphon kondoi & A. pisum; Host preferences & impact on host reproduction; Host preference, age & species selection; Reaction of host to parasite; Acyrthosiphon kondoi & A. pisum (Hemiptera), impact on reproduction Acyrthosiphon kondoi; Acyrthosiphon pisum (Aphidoidea ); Age; Hymenopteran parasite preference; Reproductive productivity; Hymenopteran parasite effects; Hymenopteran parasites; Praon pequodorum; Parasite preferences & impact on reproduction; Host preference; Praon pequodorum (Hymenoptera), age & species selection; Reaction of host to parasite; Praon pequodorum (Hymenoptera) impact on reproduction