Tadakazu NAKASHIMA, Nobuo OGURA, Masahiko TOKORO, Kiyoshi NAKAMUTA and Toshiya IKEDA
Forestry and Forest Products Research Institute, P.O.Box 16, Twkuba Norin Kenkyu
Danchi-nai, Tsukuba, Ibaraki, 305 Japan
The pine wood nematode, Bursaphelenchus xylophilus, is one of the most dangerous pests of the pine forest. To protect native pine forests, northern Europe countries embargo against the importation of wood products from the nematode detected areas . In Japan, fourth-stage dispersal juveniles of B. xylophilus (DJ-IV) are vectored by the Japanese pine sawyer, Monochamus alternatus, to healthy pine trees in early summer and attacked pine trees die mainly in autumn of the same year. In dead trees, the percentage of third-stage dispersal juveniles of the nematode (DJIII), pre-stage of DJ-IV, becomes greater toward next spring. Developmental mechanisms to DJ-IV from DJ-III have not been clarified yet. Effects of the beetle on the life cycle of the nematode in laboratory conditions without pine wood will be discussed here.
The nematodes were inoculated onto nutrient agar plates containing agar(1%), potato extract(0.2%), yeast extract(0.2%) and D-glucose(2%), in culture bottles with an unidentified fungus isolated from the entomophilic nematode, Contortylenchus genitalicola (Kosaka & Ogura, 1993), parasitizing the reproductive organs of M. alternatus. More than 4 months after inoculation, a high proportion of the DJ-III were obtained in the agar plates as a mixture of propagative juveniles and adults. The beetles have been reared on artificial diet using the method described by Kosaka & Ogura(1990). DJ-IV inducing effect of pre-pupal larvae, pupae and aduHs of the beetle were tested. The DJ-III were incubated with the beetles for 10 days in culture bottles. Then the number of DJ-IV and other stages of the nematode were counted under the microscope.
In the control, without any beetles, no DJ-IV could be found. The average percentage of DJ-IV treated with 0-day old adults was over 40%. The average DJ-IV ratio with pupae treatment was 10%. Pupal slough can induce DJ-IV at the same level as pupae themselves. Ethyl acetate extract of the sloughs also had DJ-IV inducible activity.
These results indicated that 1: cuKured DJ-III have an ability to develop into DJ-IV as have those obtained from nematode attacked pine, 2: chemical substance(s), produced by the beetle, tum on the development of DJ-III to DJ-IV.
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