Monochamus alternatusis the longicorn beetle notorious as a vector of the pinewood nematode that causes the pine wilt disease. When two populations ofM. alternatuswere subjected to diagnostic polymerase chain reaction (PCR) detection of fourWolbachiagenes, only theftsZgene was detected from one of the populations. TheWolbachia ftsZgene persisted even after larvae were fed with a tetracycline-containing diet for six weeks. The inheritance of theftsZgene was not maternal but biparental, exhibiting a typical Mendelian pattern. TheftsZgene titres in homozygoticftsZ⁺insects were nearly twice as high as those in heterozygoticftsZ⁺insects. Exhaustive PCR surveys revealed that 31 and 30 of 214Wolbachiagenes examined were detected from the two insect populations, respectively. Many of theseWolbachiagenes contained stop codon(s) and/or frame shift(s). Fluorescentin situhybridization confirmed the location of theWolbachiagenes on an autosome. On the basis of these results, we conclude that a largeWolbachiagenomic region has been transferred to and located on an autosome ofM. alternatus. The discovery of massive gene transfer fromWolbachiatoM. alternatuswould provide further insights into the evolution and fate of laterally transferred endosymbiont genes in multicellular host organisms.

The pinewood nematode (Bursaphelenchus xylophilus) is known to be the causative agent of pine wilt disease, which is transmitted from wilt-killed to healthy pine trees by the insect vector Monochamus alternatus. The second-stage propagative juvenile develops into third-stage dispersal (J_III) or propagative juveniles. The J_III develops into the fourth-stage dispersal juvenile (J_IV), a special stage for transportation, then the J_IV enters the tracheal system of adult beetles in pupal chambers in the xylem. To determine the differences in some life history parameters related to transmission between a virulent and an avirulent isolate of B. xylophilus, progression to the different life stages was investigated using two nematode isolates of different virulence, M. alternatus larvae, and pine bolts with an artificial pupal chamber. The numbers of J_IIIs and J_IVs produced around the pupal chamber by the time of beetle emergence were much smaller in the avirulent isolate than in the virulent one. The proportion of J_IIIs produced in a population around the pupal chamber (the J_III and J_IV number/the total population) and the probability of J_IIIs developing into J_IVs (the J_IV number/the J_III and J_IV number) were also smaller in the avirulent isolate. Although the probability of J_IVs boarding beetles (the initial nematode load/the J_IV number) was equal between the two isolates, the mean initial nematode load was much smaller in the avirulent isolate. The smaller initial nematode load of the avirulent isolate was ascribed to its smaller rate of reproduction and to lower production rates of J_III and J_IV. A trade-off between the virulence and transmission rate of B. xylophilus is discussed herein, taking into account the effect of the initial nematode load on the vector’s longevity and flight performance.

A putative "entomoparasitic adult form" of Bursaphelenchus luxuriosae was found in the tracheal system and body cavity of its cerambycid vector beetle, Acalolepta luxuriosa. Morphologically, this form is intermediate between the usual mycophagous adult and the phoretic dauer juvenile, i.e., it shares the primary and secondary reproductive features with the mycophagous phase but shares a degenerate digestive tract with JIV dauer juveniles. In addition, the "parasitic form" has specialized characters relative to the mycophagous phase analogous to dicyclic Hexatylina, e.g., vacuole-like dots (assumed to be sensory organs) at the anterior end, a very long vulval flap, conical female tail, and elongated male spicules. The presence of insect-parasitic juveniles has been reported in several Bursaphelenchus species, but this is the first confirmed report of a putative "entomoparasitic adult form" in the genus. Thus, the "parasitic adult form" of B. luxuriosae is hypothesized to be an autapomorphic character of this species in the genus. The physiological impact of the parasitism on the host beetle is assumed to be weak because no clear symptoms were observed in the infested beetles. Also, no nematode eggs or propagative juveniles were observed in the beetle host, suggesting that more research is needed to confirm the nature of the association (parasitic vs. endophoretic).

Analysis of the restriction fragment length polymorphism of the internal transcribed spacer region of ribosomal DNA (ITS-RFLP) is an efficient tool for classifying Bursaphelenchus nematodes at or b...