The brown citrus aphid, Toxoptera citricidus, was attacked by the parasitoid Lysiphlebus japonicus, and was actively attended by two ant species, Lasius niger and Pristomyrmex pungens. The impacts of the two ants on the parasitism of the aphid by the parasitoid were assessed experimentally at a no-pesticide mandarin grove. Aphid colonies were artificially initiated on young citrus shoots in summer. Lysiphlebus japonicus females were frequently observed foraging in aphid colonies attended by P. pungens, but rarely in colonies attended by L. niger and colonies where ants were excluded. L. japonicus females were attacked by P. pungens workers, but oviposited successfully by avoiding the ants. Large predators were excluded by both ant species from the aphid colonies, while they were abundant in ant-excluded colonies. L. niger workers often carried living aphids away from the attended colonies, whereas P. pungens removed no aphids and disregarded parasitized aphids, thereby incidentally protecting the parasitized aphids from predators. Consequently, L. japonicus-mummies were formed in great numbers in colonies attended by P. pungens, but were scarce in colonies attended by L. niger and ant-excluded colonies. Aphid-attending P. pungens workers reduced predation and hyperparasitism on L. japonicus larvae within mummies. Thus, P. pungens attending T. citricidus largely enhances parasitism by L. japonicus and its larval survival, compared with when ants are absent, whereas L. niger exerts no remarkable impact.
2003 by the Japanese Society of Applied Entomology and Zoology