Dispersal and germination traits were investigated for non-dormant seeds of black locust (Robinia pseudoacacia L.) by laboratory and field experiments. The dispersal period was ranged from early September to mid December and among this period, the non-dormant seeds accounted for overall half of the healthy seeds. In the laboratory experiment, non-dormant seeds could germinate at 15ºC or more. Though the substantial number of seedlings emerged from the non-dormant seeds in the field condition, the emergence was divided in two seasons i.e. the current autumn and next spring. The seeds sown in September-October emerged in current autumn, whereas those sown later emerged in the following spring. Since soil temperatures were less than 15ºC after November, non-dormant seeds could not germinate but keep alive under the snow during winter. Eventually, 4.3∼7.1% of non-dormant seeds could survive by the end of next growing season, and several of them reached up to more than 1 m tall or more. Most of these large seedlings developed horizontal roots. These results suggest that the non-dormant seeds which arrived at an open site may germinate immediately, and subsequently developed root sucker, which enable them to form a new stand quickly after disturbance such as flooding events at the river basin.

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We established a simulator which can estimate profits from management of individual stands for landowners under numerous sets of parameters considering; diversity of logging, growth and social conditions, and analyzed most profitable timing for thinning and clearcuttting. The assumed site is a planted Sugi (Cryptomeria japonica) forest where logging systems using forest vehicles are predominant in Yamagata Prefecture. The results showed that the longest clearcutting age of 110 years assumed in this simulation was selected as the most profitable option under almost all sets of parameters along with low discount rates such as 1%. It was difficult to gain positive soil expectation value under relatively high discount rates, indicating that forest owners have little incentive to reestablish planted forests after clearcutting. Management plans with few commercial thinnings tended to be the best choices, and repetitive commercial thinnings were preferred only when the assumed condition of logging operation including road construction and maintenance was favorable and an intensive subsidy for commercial thinning was assumed. These results indicate that stand management policies of no clearcutting with repetitive commercial thinnings promoted in the current forestry policy are less profitable in many cases.

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The pinewood nematode, Bursaphelenchus xylophilus, is the causal agent of pine wilt disease, and is vectored from wilt-killed to healthy pine trees by adults of the Japanese pine sawyer, Monochamus alternatus. This relationship between B. xylophilus and M. alternatus is greatly affected by fungi. Wood-inhabiting fungi affect the reproduction of B. xylophilus in wilt-killed trees, and then the number of B. xylophilus carried by a Monochamus beetle from wilt-killed to healthy trees. Entomopathogenic fungi prevent M. alternatus from transmitting B. xylophilus to healthy trees. Therefore, these fungi can determine the dynamics of the disease. If these fungi are effectively used and applied, we could control the disease successfully. Microbial controls of B. xylophilus and M. alternatus by fungi are being developed.

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Insects carry various endosymbiotic bacteria which can affect the reproductive capabilities of their hosts. Wolbachia is a common and widespread group of intracellular symbiotic bacteria found universally within various groups of arthropods and nematodes. They manipulate insect host reproduction by causing cytoplasmic incompatibility, feminization, male killing or parthenogenesis. The ability of Wolbachia to cause reproductive alteration drives their efficient and rapid spread in host populations. Monochamus alternatus is the longicorn beetle notorious as spreading the pine wilt disease as a vector of the pathogen, pinewood nematode. In previous studies, a Wolbachia gene was detected in M. alternatus, suggesting that this insect has been infected with Wolbachia. However, subsequent studies revealed that M. alternatus was not infected with Wolbachia but had many Wolbachia genes on an autosome, indicating that lateral gene transfer from Wolbachia to M. alternatus has occurred. The findings suggest that the Wolbachia endosymbiont that had infected M. alternatus have disappeared from the insect, leaving part of its own genome. This review highlights the interesting association of Wolbachia with M. alternatus as indicated by recent studies and proposes the future directions of research on this topic.

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The evolutional relationship between insect phoretic nematodes and their vector insects are discussed from the viewpoint of the occurrence of plant parasitism of nematodes. The xylophilus group of the genus Bursaphelenchus is a group of phoretic nematodes that use the Lamiini longhorn beetles as their carrier insects, and several species in the group, B. xylophilus, B. mucronatus, and B. firmae are known to have strong or weak virulence in pine trees. However, regardless of the phylogenetic closeness to those virulent species, B. doui does not have virulence to their host (habitat) pine trees. Then, the presence/absence of plant pathogenicity of nematodes and the life history traits of their vector insects were compared, suspecting that the beetles carrying virulent species have more opportunities to be associated with the healthy wood tissue of the plants during their feeding and oviposition. This tendency seemed also applicable to other two plant parasitic Bursaphelenchus species, B. cocophilus, and B. sexdentati. The plant parasitism (pathogenicity) of Bursaphelenchus nematodes was hypothesized to have occurred as an ability to enter and survive in the healthy plant tissue, i.e., the occurrence of plant pathogenicity seems to depend on the life history traits of carrier (vector) insects.

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The genus Iotonchium is one of the nematode groups utilizing fruiting bodies of basidiomycetous fungi. They have two ecological phases in their life cycles, i.e., mycetophagous phase living in mushrooms and insect-parasitic phase parasitizing mycetophilid gnats. In this genus, 11 species have been reported in the world, however, only 5 species, including 4 Japanese species, have been clarified the details of their life cycles. Iotonchium ungulatum, a pathogen of gill-knot disease of the oyster mushroom, is known to generate nematode-galls (knots) on the gills of fruiting bodies of Pleurotus fungi. Other Iotonchium species do not generate knots and inhabit the tissue of fruiting bodies of host fungi. Iotonchium nematodes are supposed to have close relationships with mycetophilid gnats. In the amber, their relative species has been discovered with the mycetophilid fossil. This review highlights the tripartite relationship of these organisms and discusses their evolutionary relationship and the future directions of research on this topic.

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Many fungal species are associated with bark and ambrosia beetles. The associated fungi strongly depend on the beetles for their dispersal. Some species of them have pathogenicities and some can kill host trees. In particular, Ceratocystis and Ophiostoma species invade healthy tissues of their host, resulting in destruction of the tissues. The mortalities caused by the beetle-fungi systems can be separated into two types. One is by the mass attack of beetle and associated fungi, such as the combinations of Dendroctonus ponderosae-Grosmannia clavigera, and Ips typographus-Ceratocystis polonica. And the other is by invasion of the associated fungi when maturation feeding is performed by the beetles, such as the case of Dutch elm disease system (Scolytus spp.-Ophiostoma ulmi/novo-ulmi). They are quite different modes of mortalities, although both of them are caused by the beetle-fungi systems and appear to be similar.

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Diverse array of yeasts are associated with Coleopteran beetles in forest. Some yeasts are apparently involved in the life history of beetles, albeit with less scientific attention compared to those for associated filamentous fungi. Thus, yeasts must be important but neglected members inhabiting in the forest ecosystems. In the present review, yeasts associated with Coleopteran beetles in forest are introduced. Nine families and one group of Coleoptera (i.e., Buprestidae, Bostrychidae, Cerambycidae, Chrysomelidae, Lucanidae, Nitidulidae, Platypodidae, Rhynchophoridae, Scolytidae, and fungus beetles) of interest are selected and discussed in the context of yeast-beetle symbiosis. Research on yeasts found in natural environment including beetle-associated groups has mainly been weighted on classification, identification and species description. As molecular methods have been developed and as genetic information is increasingly deposited in sequence databases, yeast species discrimination has been getting much easier. Together with these progresses, research on yeasts found from beetles and beetle-associated sources will provide a more comprehensive picture of the nature of the association.

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