Short Communication Effects of Location of Monochamus Alternatus

Nematology 16 (2014) 369-372 brill.com/nemy

Short communication

Effects of location of Monochamus alternatus (Coleoptera: Cerambycidae) pupal chambers and individual trees from which the beetles emerged on the number of Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) carried by the beetles ∗ Noritoshi MAEHARA

Pine wilt disease, caused by the pine wood nematode ried by Monochamus beetles increased with beetle body Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle weight (Linit et al., 1983; Humphry & Linit, 1989; (Kiyohara & Tokushige, 1971), is one of the most serious Aikawa & Togashi, 1998), and was much greater for forest diseases in East Asia (Kishi, 1995; Zhao et al., a virulent than an avirulent population of B. xylophilus 2008) and has also invaded Portugal (Mota et al., 1999) (Aikawa et al., 2003). Another important factor that af- and Spain (Robertson et al., 2011). The nematode is fects the number of nematodes carried by beetles is the vectored from wilt-killed to healthy pines by cerambycid fungal flora in the wood. In vitro studies showed that bee- beetles of the genus Monochamus (Mamiya & Enda, tles carried a greater number of nematodes when a blue- 1972; Morimoto & Iwasaki, 1972; Linit, 1988). The rate stain fungus, Ophiostoma minus (Hedgcock) Sydow & of disease development is directly related to the number P. Sydow, was dominant in wood around artificial pupal of nematodes in the inoculum (Kiyohara et al., 1973), chambers of the beetles, whereas the numbers of nema- and the number of nematodes that enter a healthy tree is todes decreased when Trichoderma sp. or Verticillium sp. directly proportional to the number of nematodes carried was prevalent (Maehara & Futai, 1996, 1997). The for- by Monochamus adult beetles (Togashi, 1985). Thus, to mer fungus is suitable and the latter two fungi are unsuit- understand the dynamics of disease development, it is able for nematode propagation (Fukushige, 1991; Mae- important to identify the factors affecting the number of hara & Futai, 2000). In field surveys, intense blue-stain nematodes carried by an individual beetle, which ranges on the pupal chamber walls of M. alternatus increased the from 0 to over 200 000. When beetles carry fewer than number of nematodes aggregating around such chambers 1000 nematodes, there are insufficient nematodes to kill a and the number carried by the beetles that emerged from tree without a large beetle aggregation (Togashi, 1985). these chambers (Maehara et al., 2005). Moreover, Mono- Previous studies showed that the Japanese pine sawyer, chamus beetles that emerged from chambers constructed Monochamus alternatus, that emerged from extremely just beneath the bark carried a smaller number of nema- dry or wet pupal chambers (Morimoto & Iwasaki, 1973; todes than the beetles that emerged from chambers con- Maehara et al., 2005) or logs (Terashita, 1975; Kobayashi structed in the sapwood, and there were differences in the et al., 1976; Togashi, 1989; Fukushige, 1990) carried rel- numbers of nematodes carried by beetles among individ- atively few nematodes. The number of nematodes car- ual pine trees from which the beetles emerged (Maehara

Tohoku Research Center, Forestry and Forest Products Research Institute, 92-25 Nabeyashiki, Shimo-Kuriyagawa, Morioka, Iwate 020-0123, Japan ∗ E-mail: [email protected] Received: 15 December 2013; revised: 16 January 2014 Accepted for publication: 16 January 2014 Keywords: pine sawyer, pine wilt disease, pinewood nematode.

© Koninklijke Brill NV, Leiden, 2014 DOI:10.1163/15685411-00002784 Short communication et al., 2005). However, these two findings were based on too small. In the present study, from 16 June-18 July an investigation with a small number of beetles. In the 2001, 345 Monochamus beetles emerged. The numbers of present study, I examined the effects of location of M. al- nematodes carried by individual beetles ranged from 0 to ternatus pupal chambers and individual trees from which 99 000, with a mean of 8558. There were 335 chambers beetles emerged on the number of nematodes carried by constructed in the sapwood but ten chambers were just the beetles using an adequate number of beetles for statis- beneath the bark. The number of nematodes carried tical analyses. by individual beetles from chambers beneath the bark Seven 20- to 30-year-old Japanese red pine (Pinus den- (means ± SD = 391 ± 968) was significantly smaller than siflora) trees, killed by wilt during the previous year, that from the sapwood (8802 ± 13 227) (P<0.0001). were felled and cut into 1-m-long logs at Chiyoda Exper- The result of the present study also indicated the same imental Station of Forestry and Forest Products Research tendency as the result of Maehara et al. (2005). One of Institute (FFPRI), Kasumigaura City, Ibaraki Prefecture, the possible reasons for these results is that the conditions Japan, on 15 March 2001. The 1-m-long logs were placed beneath the bark are unsuitable for B. xylophilus. in a screen cage at FFPRI, Tsukuba City, Ibaraki Prefec- We analysed the effect of individual trees on the ture, Japan. From 28-29 May 2001 the logs were cut into number of nematodes carried by Monochamus beetles, 316 pieces, 25 cm long and 2.2-24.8 cm diam. then placed except for the ten data from the chambers beneath the lengthwise in 25 cm diam. × 28 cm deep plastic contain- bark. There were significant differences in the numbers ers, with one or two logs in each container. The containers of nematodes carried by beetles among individual trees were placed in the same screen cage and each was covered from which the beetles emerged (P<0.0001) (Table 1). with a steel mesh net. The logs were watered several times This result agrees with that obtained by Maehara et al. a week during the experiment and were observed daily (2005), who used a smaller number of beetles. Maehara from June to July 2001. et al. (unpubl.) showed the possibility that trees that Upon emergence of M. alternatus from the logs, each had become asymptomatic in the year of infection by beetle was ground for 10 s using a blender in 40 ml of B. xylophilus and died in the oviposition season of tap water, and the suspension was placed in a Baermann M. alternatus the following year, were not suitable for funnel overnight to extract nematodes and to count them nematode reproduction, and adult beetles that emerged using a stereomicroscope. When the nematodes were too from such trees did not carry many nematodes. Therefore, abundant to count, the suspension was diluted and the such trees might have been included in the present study number of nematodes was estimated. The location of and that of Maehara et al. (2005), in which beetles that each pupal chamber of M. alternatus was examined, and emerged from some trees carried a smaller number of whether it was located beneath the bark or in sapwood nematodes than those from other trees. There may also was recorded. When two beetles emerged from a 25-cm- long log on the same day, the body size of the beetles and Table 1. Number of pine wood nematodes, Bursaphelenchus the diameter of the emergence holes were measured to xylophilus, carried by Monochamus alternatus that emerged determine which beetle came from which pupal chamber. from each tree of pine wilt-killed Pinus densiflora. Student’s t-test was used to analyse the differences in the numbers of nematodes carried by beetles between Tree number Number of Number of locations of pupal chambers from which the beetles beetles nematodes carried by a beetle emerged. One-way analysis of variance (ANOVA) and Tukey-Kramer’s multiple comparison test were used to 1 58 10 874 ± 18 939 ab analyse the differences in the numbers of nematodes 2 46 9729 ± 14 146 ab among individual trees. For Student’s t-test and ANOVA, 3 11 1415 ± 1624 a ± the numbers of nematodes were log -transformed. 4 21 8494 17 971 ab 10 5 49 3399 ± 6181 a Maehara et al. (2005) showed that Monochamus beetles 6 28 9135 ± 13 479 ab that emerged from chambers constructed just beneath 7 122 10 279 ± 10 432 b the bark carried a smaller number of nematodes than the beetles that emerged from chambers constructed in Values are means ± SD. Means followed by the same letter the sapwood; however, the number of beetles examined are not significantly different at P<0.05 (Tukey-Kramer’s from chambers constructed just beneath the bark was multiple comparison test).

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