Sexually mature adults of Monochamus alternatus, both male and female, are attracted to wilting pine trees for their mating and oviposition. During this time, the adult beetles continue maturation feeding on pine trees. In the present study, we examined the possibility that M. alternatus causes infection of Bursaphelenchus xylophilus on the healthy pine trees neighboring the wilting pine trees. We placed one artificially created “oviposition tree” (weakened tree) surrounded by four healthy trees in a cage and released three pairs of sexually mature, unmated male and female M. alternatus in the cage. Seventy-two hours after releasing the beetles, we investigated the number of feeding marks of M. alternatus on the surrounding healthy trees and determined the number of nematodes that invaded the healthy trees from the feeding marks. We confirmed that 31% of the surrounding healthy trees were infected with B. xylophilus. The frequency of maturation feeding on the surrounding healthy trees was as high as 89%. Although the number of detected nematodes per feeding mark was low, it occasionally reached more than 100. These results suggest that feeding of the sexually mature M. alternatus on the surrounding healthy trees might cause current year wilting and development of latent infection of the nematodes that lead to tree mortality in the following year or later.

Recently, a large proportion of urban trees planted in public infrastructural areas as parks, verge and central strip of roads, and in industrial areas have been threatened by weeds, causing stem dieback, or declining or even dying of whole tree. Serious damages to trees assumingly occur mainly because of underground tree-weed competitions with spaces, water and oxygen, and/or covering of stems with climbing weeds aboveground. Hazardous effects are usually caused by the vigorous creeping perennial weeds which extend the large systems deeply in the underground or on the soil surface, such as mugwort, goldenrod, Japanese knotweed and cogongrass having rhizomes; horsenettle and bushkiller having creeping-roots; Kudzu and other vines having stolons. These plants are easily disseminated during planting by soil-contaminated fragments of creeping organs (rhizome, root or stem) that perform as efficient propagules. Urban heat island effect and conventional mowing that stimulates weed regrowth enhance the increase of such species. Best practices for protecting tree health from present weed threats should be 1) precise control of the target hazardous species with proper method instead of overall weeding and 2) removal of their juveniles immediately on detection. Other weeds may perform desirable understories.