Influence of the Population Dynamics of a Gall-inducing Cecidomyiid and Its Parasitoids on the Abundance of a Successor, Lasioptera yadokariae (Diptera: Cecidomyiidae)

Summary

Lasioptera yadokariae (Diptera: Cecidomyiidae) is a successor in galls induced by three gall midge species. Its larvae inhabit vacated leaf galls after the primary gall inducers and their parasitoids have departed. The successor is fundamentally univoltine and its larvae feed on fungal mycelium within the galls. From 1973 to 1991, we surveyed the population dynamics and the emergence season of Pseudasphondylia neolitseae, which is one of the three gall midge species, and its parasitoids, Bracon tamabae (Braconidae) and Gastrancistrus sp. (Pteromalidae) in southern Kyushu, Japan, in order to assess the number of vacated galls that are available for the successor. Then, the proportion of vacated galls utilized by the successor was evaluated. Our data suggest that when the density of P. neolitseae or B. tamabae is high, L. yadokariae increases its population number by utilizing the abundant vacated galls after their emergence, whereas the high density of Gastrancistrus sp. does not contribute to an increase of the successor because of its delayed emergence. The high density of B. tamabae, however, would decrease the number of L. yadokariae in the following generation, because the high percentage parasitism will reduce the density of P. neolitseae, resulting in a shortage of vacated galls.