Akiomi Yamane

Genetic structure of pine sawyer Monochamus alternatus (Coleoptera: Cerambycidae) populations in Northeast Asia: consequences of the spread of pine wilt disease.

Abstract We studied the phylogeography and genetic diversity of the pine sawyer Monochamus alternatus (Hope) (Coleoptera: Cerambycidae) to understand its colonization dynamics, potential for further invasion, and potential species divergence. This species is the main vector of the pine wood nematode Bursaphelenchus xylophilus (Steiner and Buhrer), which is the causative agent of pine wilt disease in Japan. The genetic structure was studied using sequences of mitochondrial DNA and microsatellites. The phylogenetic analysis revealed two distinct lineages within M. alternatus. There is no clear boundary between haplotypic distributions of the two clades. Coalescence should have been extended by population subdivision. There might also be a fusion of the two distinct populations, and both are completely saturated. Analysis of the microsatellite genotypes of populations in Japan showed a complex genetic structure. Estimates of overall population differentiation (FST) were significantly different from zero. The populations are thought to be at demographical nonequilibrium or to show restricted gene flow among prefectures. Although neighboring populations often had similar genetic compositions, significant isolation by distance in the total population was not detected. It is suggested that population expansion may have occurred not only by natural dispersal on a small scale, but also by long-distance dispersal likely enhanced by the relocation, (by humans) of infested wood. Our data suggest that M. alternatus is a species capable of dispersing over a large area, and therefore, multiple invasions of M. alternatus from distant areas is a possibility.

Performances of four chemicals with floral scents as attractants for longicorn beetles (Coleoptera: Cerambycidae) in a broadleaved forest

White plastic insect traps (manufactured by Sankei Chemical Co., Ltd.) equipped with four chemicals with floral scents, namely, benzyl acetate, methyl benzoate, methyl phenylacetate and linalool, were set from June 28 to August 9, 1996. The traps were placed in a Japanese beech (Fagus creata) forest, Minakami, Gunma Prefecture, Central Japan, and trapped longicorn beetles were collected weekly. The greatest number of species and individuals belonged to the subfamily Lepturinae dominated by the genusPidonia. No significant differences were observed in the performances of the above four chemicals in either the total number of species or of individuals. However, more Lamiinae species were captured in the traps with methyl phenylacetate, than in those with methyl benzoate.

Evaluation of beetle capture in traps as compared with manual capture on flowers in a long-term investigation in a beech forest

Beetle samples captured by traps were compared with those captured manually on flowers in a beech forest in Central Japan. Plastic traps (Sankei Chemical Co., Ltd.) equipped with benzyl acetate were set up from the 2nd of June to the 8th of September 1994, and all beetles captured were collected every week. Beetles were also captured on wild flowers blooming along the forest road. The traps captured 21,650 individuals of 169 species in 37 families. On the other hand, 971 individuals of 77 species in 19 families were captured on the flowers. All of the families and 57 (74%) species of the beetles captured on the flowers were also captured by the traps; all of the species with more than five individuals captured on the flowers were also trapped, except for one species. The present trap system is considered to be useful for faunal monitoring of flower-visiting Coleoptera, because the beetle fauna found on wild flowers was virtually covered by the trap capture.

Glycolytic Activities in the Larval Digestive Tract of Trypoxylus dichotomus (Coleoptera: Scarabaeidae)

The larvae of the Japanese horned beetle, Trypoxylus dichotomus (Coleoptera: Scarabaeidae: Dynastinae), are an example of a saprophage insect. Generally, Scarabaeid larvae, such as T. dichotomus, eat dead plant matter that has been broken down by fungi, such as Basidiomycota. It is thought that β-1,3-glucan, a constituent polysaccharide in microbes, is abundant in decayed plant matter. Studies of the degradation mechanism of β-1,3-glucan under these circumstances are lacking. In the current study, we sought to clarify the relationship between the capacity to degrade polysaccharides and the food habits of the larvae. The total activities and optimum pH levels of several polysaccharide-degrading enzymes from the larvae were investigated. The foregut, midgut and hindgut of final instar larvae were used. Enzymatic activities were detected against five polysaccharides (soluble starch, β-1,4-xylan, β-1,3-glucan, pectin and carboxymethyl cellulose) and four glycosides (p-nitrophenyl (PNP)-β-N-acetylglucosaminide, PNP-β-mannoside, PNP-β-glucoside and PNP-β-xyloside). Our results indicate that the digestive tract of the larvae is equipped with a full enzymatic system for degrading β-1,3-glucan and β-1,4-xylan to monomers. This finding elucidates the role of the polysaccharide-digesting enzymes in the larvae, and it is suggested that the larvae use these enzymes to enact their decomposition ability in the forest environment.

Genetic Structure of Monochamus alternatus in Japan

Recent progress in molecular ecological methods has enabled us to study genetic differentiation among populations. By elucidating the genetic structure, we can trace the history of populations and to infer ongoing patterns of migration. In this chapter, we review the population structure of the pine sawyer Monochamus alternatus detected by microsatellite markers and mitochondrial DNA. First, the process of population expansion is inferred from the genetic structure determined from populations of Japan, China and Taiwan populations by mitochondrial DNA and microsatellite markers. Secondly, microsatellite markers are used to show the pine sawyers’ dispersal route in the past in the northern part of Honshu Island, Japan, which is the frontier of the area damaged by pine wilt disease. Finally we discuss further subjects in studies of the sawyers’ dispersals.