Many conifers form traumatic resin canals and secrete resin. Traumatic resin canal formation is induced by various stimuli, and involved in the prevention of the insect attack and fungal invasion. Traumatic resin canals are formed near the cambium either in xylem or in phloem, and both traumatic resin canals take 1 to 2 months to develop to maturity. Ethylene application can artificially induce the traumatic resin canal formation and enhance the resin production, suggesting that the stress ethylene, which is produced by conifers suffering stresses, is related with the traumatic resin canal system. Continual stimuli that are added by the activities of insects and fungi likely promote the ethylene production than temporary ones such as mechanical wounds, and increase the area of the traumatic resin canal distribution and the amount of secreted resin. Ethylene production is induced by abiotic stresses. There is a possibility that combination of biotic and abiotic stresses leads the conifers to copious ethylene production.
In order to elucidate the cause of the amount of emerging adult of the Japanese horntail Urocerus japonicus varying on host trees, we investigated the relationship between the number of emerged adults from felled logs of Japanese cedar Cryptomeria japonica and several factors on U. japonicus and on its host trees. The number of emerged adult correlated with both of the number of oviposited pinholes and of hatched larvae. Furthermore, there was a strong correlation between the number of emerged adults and the diameter of host tree. There was not a correlation between the number of emerged adults and the percentage parasitism of Megarhyssa praecellens. Also the moisture content of host trees correlated with the number of emerged adults, hatched ratio and emerged ratio of U. japonicus, respectively. These relations were explained with an assumed model on the number of oviposited pinholes, the number of hatched larvae, the number of emerged adults, the diameter of host trees and the moisture content. We estimated that the size of host tree was one of the regulating factors on the number of emerging adults of U. japonicus through the moisture content.