The Japanese pine sawyer, Monochamus alternatus Hope, is the primary vector of the pinewood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, the causative agent of pine wilt disease in East Asia. The range of B. xylophilus expands through the dispersal capability of its vectors and transport of host trees infested with the pathogenic nematode and its vector. Outbreaks of M. alternatus populations occur together with the epidemics of pine wilt disease, because the insect reproduces on host trees recently killed by the disease. We measured some dispersal and life‐history traits of adults for four years to determine the change in flight capability and life history of a field population of beetles in relation to an outbreak. The population monitored exhibited an outbreak and subsequent collapse. The greatest mean body mass, largest area of hind wings, smallest wing load, and shortest preoviposition period were observed in the year of outbreak. By contrast, there was no difference in the ovariole number between pre‐outbreak (latent) and outbreak years. The greatest mean hind wing area and smallest wing load suggest likely result in greater flight performance. As other studies showed, adult body mass is related positively to the flight performance and oviposition rate. Moreover, a shortened preoviposition period leads to a high reproduction rate. Thus, adults in outbreak populations are “superdispersers” because they are likely to have enhanced flight capability and reproduction power. This suggests that M. alternatus populations at the onset of a population outbreak enhance the expansion rate of B. xylophilus range more than those during the latent and pre‐outbreak periods.
Cerambycid adults of the genus Monochamus transmit the pine wood nematode (Bursaphelenchus xylophilus [Steiner et Buhrer] Nickle), the causative agent of pine wilt disease. To confirm the transmission of B. xylophilus between vector species, nematode‐infected Monochamus alternatus Hope and nematode‐free Monochamus saltuarius (Gebler) adults were paired and their behaviour was observed for 107–220 min. In three pairs that exhibited mounting without copulation, nematode transmission occurred, whereas it was not found in another pair without mountings. The effect of nematode transmission between different vector species on the invasion biology of B. xylophilus is discussed.
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