none The predominance of females over males was found in each sample of Lysiphlebus delhiensis collected as adults or parasitised aphids except in smaller ones (where number of emergents was less than 10) which were collected either early or late in the season. The mean sex ratio (proportion of females in the population) of the progenies (p@u- = 0.625) collected from the field as parasitised aphids varies significantly from an expected sex ratio p@u- = 0.50). Virginity of females in the field population was observed rarely, reflecting the existence of an efficient mate finding and copulatory mechanisms in the species. Males are polygynous. A single male was observed to mate with 24 females in a succession within 8 h. The sex ratio of the progeny of first 5 females (mated successively in a succession with a single male) was greater than or equal to 0.70. The results are discussed in the view of earlier models. Reproduction; Reproductive behaviour; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Population dynamics; Population structure; Land and freshwater zones; Oriental region Lysiphlebus delhiensis (Braconidae); Mating; Observations & effect of successive matings on progeny sex ratio; Pair formation; Mate location success; Polygamy; Successive matings effect on progeny sex ratio; Hemipteran hosts; Rhopalosiphum maidis; Parasite sex ratio; Population sex ratio; Seasonal variation, adults & progeny from hemipteran host; India; Uttar Pradesh; Gorakhpur district, variations & influencing factors Rhopalosiphum maidis (Aphidoidea); Hymenopteran parasites; Lysiphlebus delhiensis; Parasite sex ratio; India; Uttar Pradesh; Gorakhpur district; Hymenopteran parasite sex ratio