Koichi Sone

Isolation of endophytic fungi from leaves of Pasania edulis and their within-leaf distributions

Abstract Endophytic fungi were isolated from leaves of Pasania edulis, one of the most important trees of the warm temperate forests in southern Kyushu, by the surface sterilization method using H2O2 as a sterilizing agent. From a tree in the Experimental Nursery of Kagoshima University, located at the city of Kagoshima, Phyllosticta sp. and Colletotrichum spp. were frequently isolated. From a stand in a laurel forest in Mt. Takakuma, an ascomycetous fungus (Ascomycete sp. 1) and Phomopsis sp. were frequently isolated. Phyllosticta sp. was isolated more frequently from petiole segments and leaf segments with midrib and Phomopsis sp. from petiole segments and leaf-base segments with midrib than other segments. Colletotrichum spp. were isolated less frequently from petioles and Ascomycete sp. 1 from petiole segments and leaf-base segments with midrib than other segments. As possible causes of such biases in within-leaf distributions of the endophytes, differences in infection modes and negative interactions of major endophytes within leaves are suggested.

Hoarding of acorns by granivorous mice and its role in the population processes of Pasania edulis (Makino) Makino

In order to evaluate the role of granivorous mice, Apodemus speciosus Temminck and Apodemus argenteus Temminck, in the regeneration of Pasania edulis (Makino) Makino, an evergreen tree, we conducted field studies examining acorn crops, the population dynamics and hoarding behavior of mice and pre- and postdispersal acorn predation in an evergreen broad-leaved forest dominated by P. edulis in Kagoshima, southern Japan. The study was conducted from 1994 to 2000. Apodemus mice selected sound acorns and hoarded them in the soil after transporting them for distances ranging from 5.4 to 19.9 m. This behavior appeared to be beneficial to the establishment of seedlings of P. edulis. However, the positive effects were negated by a high rate of recovery of the acorns hoarded by the mice. A life-table analysis of five cohorts of P. edulis indicated that postdispersal predation of acorns by Apodemus mice was a major contributor to annual variation in the number of new seedlings. A considerable number of acorns germinated only in years with a good acorn crop and a low level of resident mice. These results suggest that Apodemus mice are serious acorn predators rather than important dispersers. After germination, acorns were attacked by the acorn borer at a high rate. From these results, we can conclude that acorn production probably makes a smaller contribution to the regeneration of P. edulis than coppice shoot production at the study site.

Acorn hoarding by the field mouse,Apodemus speciosus Temminck (Rodentia: Muridae)

We studied population changes of the field mouse,Apodemus speciosus Temminck, by live trapping in a mixed stand of cypress and broad-leaved trees at Tama Forest Science Garden during the period from October 1991 to March 1994. We also used radiotelemetry to investigate acorn hoarding. The number of mice captured in 1992 was three to ten times higher than that in either 1991 or 1993. The home ranges of resident mice overlapped greatly, but a path and differences in the vegetation structure may have affected the home range of individuals. From June 1992 to April 1993, mice actively transported and hoarded acrons. Individuals hoarded 70% of the acorns in their home ranges within one day after release. This species was a typical scatter-hoarder and hoarded a single acorn at each cache site. Mice buried acrons in the soil at the first hoarding, but recovered and carried them into their nests later. Although more than 50% of the acorns were buried 0–5 cm deep, where the condition for germination seemed to be good, mice recovered and ate all cached acorns. Mice relocated acorns farther from the original food station as they repeated hoarding. Mice transported acorns an average of about 15–18 m (range: 2.2–49.8 m) before they ate them. From May 1993 to March 1994, the hoarding behavior of mice was not active. Most acorns were left at food stations or cache sites for more than three months. Acorn hoarding byA. speciosus probably contributes little to the dispersal and regeneration of acorn-producing trees in years with a high rodent density.

Application of radiotelemetry to the survey of acorn dispersal by Apodemus mice.

We examined the applicability of radiotelemetry to studies of acorn dispersal by Apodemus mice and compared its efficiency with the of this spool-and-line method. Installation of a transmitter (2.2 g) onto acorns did not interfere with the transporting and feeding behavior of the mice. We were able to detect all transmitter-installed acorns and follow the daily changes in the sites in which they were hoarded, while we missed 59% of the spool-tied acorns due to mice breaking the threads. Mice carried transmitter-installed acorns farther than spool-tied ones. The radiotelemetry method is superior to the spool-and-line method and useful for the study of hoarding behavior in rodents.

Role of interspecific competition in the coexistence ofApodemus argenteus andA. speciosus (Rodentia: Muridae)

Reciprocal-removal experiments with two replicates were conducted to test for the role of interspecific competition in the coexistence ofApodemus argenteus andA. speciosus. Population density, rate of appearance of new (unmarked) individuals, reproduction, survival rate and habitat use were monitored during pre- and removal periods. In both removal experiments, the removal ofA. argenteus had little effect onA. speciosus, while that ofA. speciosus affected several population characteristics ofA. argenteus. Namely, the removal ofA. speciosus shifted the distribution ofA. argenteus to the habitat with a denser shrub cover in one experiment. Also, the removal increased the population densities and appearance rates of new individuals ofA. argenteus in another experiment. Interspecific interactions between the two species appeared to be a one-way action fromA. speciosus toA. argenteus. In removal periods in both experiments, the rates of appearance of new individuals in each species were the highest on the grid where that species was removed. These results suggest that, though interspecific competition occurred between the two species, intraspecific competition had greater effects than interspecific competition on the abundance and habitat use ofA. argenteus andA. speciosus. This implies that the fundamental niches ofA. argenteus andA. speciosus differ potentially, which may play an important role in the coexistence of the two species.

Life History of the Red Palm Weevil, Rhynchophorus ferrugineus (Coleoptera: Dryophtoridae), in Southern Japan

ABSTRACT We surveyed the life history of the red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Dryophthoridae), in southern Japan, including seasonal changes in the flight activity of adults and composition of R. ferrugineus in different developmental stages in a total of 17 infested Phoenix canariensis trees which were cut down in 2003–2005. The flight of adults began in Mar, showed some peaks in summer and autumn, and ceased in mid-Dec. Various stages of individuals inhabited infested P. canariensis trees throughout the year. The composition of individuals at different stages in late fall was dependent on the resource (white intact tissue) availability in P. canariensis trees. In P. canariensis trees where considerable resource remained, all stages of larvae, pupae, and adults were found, whereas in palm trees with no resource, few young- and medium-stage larvae were observed. The temperature in the infested part of a palm trunk was 30°C or higher even in winter. From these results, we view the life history of R. ferrugineus in southern Japan as follows: Adults emerge from host trees in spring and continue to attack host trees until late fall. Rhynchophorus ferrugineus grows even in winter if intact tissue remains at the peripheral part of trunks, and there may be 3 or 4 generations per year. A cold winter probably does not have any negative effects on successful colonization of R. ferrugineus in Japan.

Spatial distribution pattern of attack of the oak borer,Platypus quercivorus (Murayama) (Coleoptera: Platypodidae), and scolytid ambrosia beetles (Coleoptera: Scolytidae) on fresh logs

The spatial distribution patterns of the attack on fresh logs ofPasania edulis was studied for the oak borer,Platypus quercivorus (Murayama), and two species of Scolytid ambrosia beetles,Xylosandrus crassiusculus (Motschulsky) andXyleborus attenuatus Blanford, in 1994 and 1995. On the logs where onlyP. quercivorus attacked, the entry holes were distributed uniformly when attack intensity was low. However, the distribution pattern became more aggregated with the increase in attack intensity. On logs where bothP. quercivorus and the two Scolytid species attacked, there was a negative association between the spatial distribution of the entry holes ofP. quercivorus and that of scolytids. Simultaneous attack of two scolytids also increased the degree of aggregation of the entry holes ofP. quercivorus. The entry holes of scolytids were distributed in groups irrespective of the attack intensity of scolytids andP. quercivorus. These results suggest an asymmetrical interspecific relationship betweenP. quercivorus and scolytids. Concentration of the entry holes ofP. quercivorus in a small area may cause a considerable decline in the reproductive success in the galleries constructed there.

Potential role of frugivorous birds in the recovery process of forest vegetation after feral goat eradication in Mukojima Island, the Bonin Islands

Some introduced frugivorous birds disperse introduced plants and are thus a substitute for extinct native birds. Introduced birds have negative and/or infrequently positive effects on local ecosystems. It is important for management of the ecosystems to understand the relationships between native and introduced frugivorous and plant species. In this study, we elucidated these relationships in Mukojima Island, the Bonin Islands, where was anthropologically deforested and Japanese White-eye Zosterops japonicus and some plants were already introduced. We examined the habitat selection of frugivorous birds, actual dispersed seeds in bird feces, and the distribution of the potentially dispersed plant species. The Japanese White-eye and the native, Blue Rockthrush Monticola solitarius, were dominant on this island. The former mainly used the forest area and dispersed only small seeds and frequently introduced plant seeds. The latter mainly used the open area and dispersed both small and large seeds. Some small-seed plants occurred not only in the forest but also in the open area. Their seedlings were distributed farther from their adult trees than the large-seed species. These indicate that small-seed plants would be more spread than the large-seed plants because the two bird species disperse their seeds in different environments. This introduced bird species may be important in vegetation recovery, although it may contribute to the distribution of introduced plants on this island.

Changes in Foraging Behavior of Two Species of Field Mice, Apodemus speciosus Temminck and A. argenteus Temminck (Rodentia: Muridae), in the Response to Artificial Illumination

Predation hazard is one of the most important factors that affect foraging behavior. Light intensity is an indirect measure of a predation hazard for nocturnal rodents. In 1988 and 1989, I conducted laboratory experiments to reveal the effects of the predation hazard on foraging behavior of two species of field mice,Apodemus speciosus Temminck andA. argenteus Temminck (Rodentia: Muridae), which co-exist in many areas in Japan. I released a mouse into the experimental arena, where I set one nest box and two food stations (one near and the other far from the nest box), and recorded the foraging behavior for sixA. speciosus and sixA. argenteus mice. I planned to illuminate the experimental arena when the mouse left the nest box to mimic a predation hazard during excursion. The light treatment decreased the time the mouse spend outside the nest box, the duration of an excursion, the number of visits to the food station far from the nest box, and the number of peanuts handled at the food station far away. Mice handled food more intensely at the food station near to the nest box and tended to carry more foods back to the nest box and eat them there during the light treatment period than the control period. These behavioral changes, which seemed to be adaptive to avoid the predation hazard in the field, were more apparent in smaller mice,A. argenteus, than larger mice,A. speciosus.

Abundance-dependent transmission of the pinewood nematode, Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae), to the Japanese pine sawyer, Monochamus alternatus (Coleoptera: Cerambycidae), adult in its pupal chamber

The transmission ratio of the pinewood nematode (PWN), Bursaphelenchus xylophilus, to the emerging adult Japanese pine sawyer (JPS), Monochamus alternatus, in its pupal chamber is a determinant of the number of the nematodes carried by JPS beetles. To investigate the factors affecting the transmission ratio, we counted the number of the nematodes carried by 36 newly emerged JPS beetles and the number remaining in and around their pupal chambers, and then estimated the transmission ratio (the number of nematodes carried by a JPS adult as a percentage of the total number of nematodes aggregating in and around its pupal chamber). The total number of nematodes aggregating in and around a pupal chamber ranged from 0 to 19,041, and the number of nematodes carried by a beetle ranged from 0 to 18,920. The transmission ratio correlated with neither the water content of the wood around the pupal chamber nor the degree of wood discoloration caused by blue-stain fungus. The transmission ratio varied with the abundance of the nematodes aggregating in and around the pupal chamber. In pupal chambers with more than 1,000 nematodes, almost all the nematodes were transmitted to the beetle. However, in pupal chambers with fewer than 1,000 nematodes, the transmission ratio varied greatly, from 0 to 100%. These results suggest that aggregation of many PWNs in the pupal chamber might stimulate transmission of the PWNs to the JPS adult and that this abundance-related transmission might contribute to the large variation in the number of PWNs carried by the JPS beetle.