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Transmission of the causing agent of the pine wilt disease, Bursaphelenchus xylophilus (Steiner & Buhrer) (Nematoda: Aphelenchoididae), among Pinus pinaster Aiton (Pinaceae) trees in Portugal is known to occur during pine sawyer, Monochamus galloprovincialis (Olivier) (Coleoptera: Cerambycidae), adult feeding on twigs of healthy trees or during female oviposition on dying or dead trees. Still, the disease does not affect the other potentially susceptible local pine species, Pinus pinea L. Several experiments evaluated the suitability of P. pinea as a host for M. galloprovincialis feeding, oviposition, and progeny development. Feeding responses were studied in two-choice experiments pairing P. pinea twigs with P. pinaster, Pinus halepensis Miller, Pinus sylvestris L., Pinus uncinata Miller, and Pinus nigra Arnold. Another test assessed the effect of increased dosages of limonene applied to P. pinaster twigs on M. galloprovincialis feeding. Oviposition preferences for P. pinaster, with either intact or manipulated bark thickness, P. pinea, and P. sylvestris were also studied in two-choice tests. Finally, suitability of P. pinea as a substrate for the development of M. galloprovincialis offspring was tested. Results showed that P. pinea could be an acceptable host for the pine sawyer feeding under laboratory conditions. Only P. sylvestris and P. pinaster twigs were significantly more consumed than those from P. pinea. Control and limonene-treated twigs were eaten similarly, but feeding decreased as dose increased, suggesting an inhibitory effect of limonene. Oviposition wounds, both egg-containing and eggless, occurred more on P. pinea than on P. sylvestris or P. pinaster, though the percentages of wounds indicating successful egg laying were significantly higher on P. pinaster and P. sylvestris. Monochamus galloprovincialis progeny completed its development on P. pinea, but emergence was lower than on P. sylvestris, likely due to higher mortality during egg and early larval stages. Thus, results on vector host preferences do not explain the observed absence of nematode-killed P. pinea trees in the field. |
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