Seasonal differences in the abundance of an ant-adapted parasitoid, Lysiphlebus japonicus (Hymenoptera: Aphidiidae), in ant-attended colonies of the spirea aphid Aphis spiraecola (Hemiptera: Aphididae) on citrus: comparison for two ant species, Lasius japonicus and Pristomyrmex punctatus (Hymenoptera: Formicidae)

Abstract

The parasitoid Lysiphlebus japonicus Ashmead is able to exploit aphids attended by ants and is therefore a candidate for a biological control agent of ant-attended aphids, but there is little information on the factors that influence changes in the population of this parasitoid. The species of aphid-attending ants may be a factor in seasonal fluctuations in its occurrence. This study experimentally examined how each of the two ant species Lasius japonicus Santschi and Pristomyrmex punctatus Smith influences the seasonal change in the abundance of this ant-adapted parasitoid in the colonies of the spirea aphid Aphis spiraecola Patch, which the ant species attends, on citrus in Japan. The numbers of aphid mummies formed by the parasitoid and ovipositing parasitoid females in the ant-attended aphid colonies in late spring (mid- to late May) were compared with the numbers in mid-summer (late July to mid-August) for each ant species. Significantly more mummies were found in the aphid colonies attended by P. punctatus than in the colonies attended by Lasius japonicus in both seasons. The number of mummies in P. punctatus-attended aphid colonies did not differ significantly between the two seasons. In the Lasius japonicus-attended colonies, however, the mummy numbers were significantly reduced in mid-summer compared with late spring. The seasonal distribution of mummy numbers was significantly dependent on the aphid-attending ant species. The number of parasitoid females that deposited eggs in the ant-attended aphid colonies varied in a similar manner to the number of mummies. Thus, the species of aphid-attending ant determines the seasonal difference in the abundance of the ant-adapted parasitoid in ant-attended aphid colonies. Possible underlying mechanisms for this result and its implications for the biological control of ant-attended aphids on citrus are discussed.