We studied the population structure and flowering and fruiting characteristics of two populations of the endangered tree Padus avium var. avium, in Goshogawara and Itayanagi, Aomori Prefecture, Tohoku region. The two populations comprised 151 stands with the stem girth at breast height of 15 cm or higher, which were distributed across 15 patches. The number and local density of the patches were lower in Goshogawara than in Itayanagi. The patches in Itayanagi were estimated to bear 20 % more hermaphrodite flowers than the patches of the same size in Goshogawara. Furthermore, the fruit set of the two populations was rather low (0.9 %). Fruit set per patch significantly differed between the two populations, and the weighted means of fruit set using patch size as the weight also indicated substantial differences in the fruit set between the two populations. In Itayanagi, patches with larger stems tended to exhibit higher fruit set. In pollination experiments, the species exhibited partial self-incompatibility and the pollen limitation index of the two populations was 0.98–0.99, suggesting that limited cross-pollination results in a low fruit set. Also, cross-pollinated flowers achieved a relatively low fruit set (17 %), suggesting that factors other than limited cross-pollination are associated with the fruit set. Further studies elucidating the causes of low fruit set are essential for the effective conservation management of P. avium var. avium, in the Tohoku region.

View full abstract

To examine the applicability of parasitic nematodes derived from the wood-boring insects as a biological control agent of M. alternatus, we investigated the prevalence of a species of parasitic nematode in Tomicus piniperda adults caught in the field. Among the 37 male and female adults of T. piniperda dissected, 31 (83.8 %) harbored parasitic nematodes in their hemocoels, with a maximum number of 132. We identified the parasitic nematode as Parasitorhabditis sp. via morphological observation of the adult nematodes. One to 123 nematodes originated from the 13 T. piniperda were incubated with each of the 13 mature M. alternatus larvae in a 6 cm petri dish. Most of the larvae pupated and emerged normally; however, two larvae did not pupate for 90 incubation days and one larva died as a pupa. No nematodes were detected in any of the 13 M. alternatus tested. However, the nematodes used in this study may not have been in a developmental stage suitable for invading into the host’s body. Hence, further studies, such as confirmation of infective stage of the nematode and inoculating them to the beetle, and selection of vulnerable stage(s) of beetle to the nematode, are needed to accurately estimate the nematode’s parasitic effect on M. alternatus.

View full abstract

[in Japanese]

View full abstract