A chronosequence of understorey parasitic wasp assemblages in secondary broad-leaved forests in a Japanese ‘satoyama’ landscape


Kaoru Maeto, Laboratory of Insect Science, Graduate School of Agricultural Science, Kobe University, Rokkodai-cho 1-1, Nada-ku, Kobe 657-8501, Japan.
E-mail: maeto@kobe-u.ac.jp


Abstract.  1. To infer the effects of forest aging on the abundance, genus richness and diversity, and genus composition of understorey parasitoids, we investigated the assemblages of braconids collected in Malaise traps in a chronosequence of secondary broad-leaved forests (4–128 years old) in the satoyama landscape in the cool-temperate region of central Honshu, Japan.

2. Multivariate linear regression analysis indicated that the abundance of braconid parasitoids was affected by forest age (time since clear-cutting) in the secondary broad-leaved forests, although the effects on genus richness and diversity were not statistically supported.

3. The abundance of herbivore parasitoids decreased significantly with forest age. This is probably caused by the decline of insect herbivores associated with the decrease in forest floor vegetation along the chronosequence.

4. The opposite trend was observed for detritivore parasitoids, which significantly increased in abundance with forest age, probably along with forest floor litter mass, though no significant change in the abundance of wood-borer parasitoids was observed with forest age.

5. Genus composition of braconid parasitoids was affected by forest age, as determined by canonical correspondence analysis. Genera of detritivore parasitoids were mostly confined to older plots, those of herbivore parasitoids were rather abundant in younger plots, and those of wood-borer parasitoids were more broadly distributed.

6. Therefore, we conclude that the presence of mixed forest stands of various age classes at the landscape level would contribute to the conservation of diverse assemblages of host insects and their parasitoids.