To elucidate how ants use two simultaneously present food resources, honeydew and extrafloral nectary (EFN), in relation to aphid density, we first examined ant recruitment patterns with different densities of aphids on Vicia faba L. (Leguminosae) with EFN in two field sites with different species composition of ants. Three species of ants visited plants of V. faba at each site, but two different species, Tetramorium caespitum Linnaeus (Hymenoptera: Formicidae) and Lasius niger L. (Hymenoptera: Formicidae) were the main visitors on plants of V. faba at the different sites. The numbers of ants of T. caespitum and L. niger visiting a plant increased as the density of Aphis craccivora Koch (Homoptera: Aphididae) per plant increased. The correlation between the numbers of L. niger and Aphis craccivora was higher than that between the numbers of T. caespitum and A. craccivora. Second, we examined in a laboratory how two ant species, T. caespitum and L. niger, use the honeydew of A. craccivora and V. faba’s EFN. As the aphid density per plant increased, the numbers of ants of T. caespitum and L. niger using honeydew increased, and conversely, those using extrafloral nectar decreased. This study showed that ants shifted their collection pattern from extrafloral nectar to honeydew at higher density of aphids per plant, and it may be considered that honeydew is more attractive for ants than EFN at higher aphid density, because ants react sensitively to differences in the quality and/or quantity of both extrafloral nectar and honeydew.
Annals of the Entomological Society of America
Vol. 96 • No. 4
Vol. 96 • No. 4