The impacts of two species of ants (Lasius niger and Pristomyrmex pungens) attending the cotton aphid (Aphis gossypii) on the number of emerging adults of the aphid's primary parasitoid (Lysiphlebus japonicus) and hyperparasitoids were assessed experimentally at a no-pesticide mandarin grove. L. japonicus females were observed foraging frequently in aphid colonies attended by either ant species, with more females in P. pungens-attended than in L. niger-attended colonies, but rarely in aphid colonies where ants were artificially excluded. Females were less often attacked by P. pungens workers than by L. niger workers, so that they stayed longer and oviposited into more aphids in P. pungens-attended than in L. niger-attended colonies. Attendance by each ant species reduced predator numbers in aphid colonies, compared to colonies where ants were absent, although P. pungens was slightly less effective in repelling predators. Therefore, both ant species incidentally protected parasitized aphids from predators. Consequently, L. japonicus-mummies were abundant in colonies attended by either ant species, with more mummies in P. pungens-attended colonies, and were scarce in ant-excluded colonies. The hyperparasitism and predation on L. japonicus larvae within mummies occurred more frequently in P. pungens-attended than in L. niger-attended colonies, but mummy predation rate was only 20% in the former. As a result, the number of emerging L. japonicus adults did not differ significantly between aphid colonies attended by the two ant species, but significantly more hyperparasitoids emerged in colonies attended by the relatively less aggressive P. pungens than in colonies attended by L. niger. Nutrition; Diet; Prey; Reproduction; Reproductive behaviour; Behaviour; Agonistic behaviour; Associations; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Predators; Land and freshwater zones; Palaearctic region Insecta; Insect prey; Aphis gossypii (Hemiptera) & Hymenoptera; Protection from predation afforded by hemipteran/hymenopteran mutualism; Japan Terebrantia; Hemipteran hosts; Aphis gossypii; Hymenopteran hosts; Lysiphlebus japonicus; Hyperparasitism; Japan; Honshu; Shizuoka; Shimizu City; Hyperparasites in hymenopteran parasites of hemipteran host, influence of host mutualists Lysiphlebus japonicus (Aphidiidae); Egg laying; Hymenopteran parasites; Terebrantia; Hemipteran hosts; Aphis gossypii; Parasite distribution & performance & hyperparasite incidence, influence of host mutualists; Hyperparasitism; Insect predators; Japan; Honshu; Shizuoka; Shimizu City; Hemipteran host hymenopteran mutualists influence on parasites & hyperparasites Phaenoglyphis (Cynipidae ); Syrphophagus (Encyrtidae ); Asaphes suspensus; Pachyneuron aphidis (Pteromalidae ); Dendrocerus (Ceraphronidae ); Hyperparasitism; Lysiphlebus (Hymenoptera) in hemipteran primary host, effect of host mutualists; Japan Lasius niger; Pristomyrmex pungens (Formicidae ); Aggressive behaviour; Mutualism; Aphis gossypii (Hemiptera); Aggressiveness significance in impact of associate parasites; Japan; Honshu; Shizuoka; Shimizu City; Mutualists of Hemiptera, influence on associate parasites, hyperparasites & predators Aphis gossypii (Aphidoidea); Mutualism; Lasius niger & Pristomyrmex (Hymenoptera); Mutualist aggressiveness, influence on parasites; Hymenopteran parasites; Lysiphlebus japonicus; Hyperparasitism; Insect predators; Japan; Honshu; Shizuoka; Shimizu City; Hymenopteran mutualists influence on parasites, hyperparasites & predators none