Laboratory experiments were carried out to clarify the bodyguard effects for the aphid, Aphis craccivora Koch, against predatory ladybeetle larva, Coccinella septempunctata L., by two ant species, Tetramorium caespitum Linnaeus and Lasius niger L. In particular, we examined the effectiveness of protection for aphids as related to ant activities on a plant. The number of attacks on a ladybeetle larva by ants until the ladybeetle larva dropped from the plant did not differ between the two ant species, suggesting similar aggressiveness of the two ant species. However, the number of attacks per min by L. niger was five times greater than that by T. caespitum. Consequently, the residence time of the ladybeetle larva was shorter and the proportion of aphids eaten was lower in the presence of L. niger than in the presence of T. caespitum. Thus, the encounter rate between ants and predators is one of the most important factors for bodyguard effects on aphids, resulting from the markedly different foraging behaviors of the two ant species.
2003 by the Japanese Society of Applied Entomology and Zoology