Factors enabling Epinotia granitalis (Lepidoptera: Tortricidae) overwintered larvae to escape from oleoresin mortality in Cryptomeria japonica trees in comparison with Semanotus japonicus (Coleoptera: Cerambycidae)

Abstract

The factors involved in the successful escape of overwintered larvae of Epinotia granitalis from host oleoresin in the phloem of Cryptomeria japonica were studied. The mortality, period, and body weight of E. granitalis overwintered larvae while feeding on the phloem of C. japonica were compared with the same parameters for Semanotus japonicus larvae. The seasonal fluctuation in the ability of C. japonica to form traumatic resin canals in the phloem was also assessed. The oleoresin mortality of E. granitalis was low compared with that of S. japonicus. Although both species started feeding on approximately the same date in spring, the feeding period of E. granitalis was only about 24 days, showing that E. granitalis faced the danger of host oleoresin for a shorter period than S. japonicus. The larval weight of E. granitalis was consistently greater than that of S. japonicus through the phloem-feeding period of E. granitalis, and the growth rate was also higher in E. granitalis, suggesting that E. granitalis had a better ability to avoid host oleoresin. These results demonstrated that not only the feeding habits, that is, the tendency of a single larva to feed at several sites, but also the shorter feeding period and larger body size were probably the important factors facilitating escape of E. granitalis from host oleoresin mortality. Furthermore, the ability of C. japonica to form traumatic resin canals increased after the starting date of larval feeding in spring. Because E. granitalis finished feeding before the culmination of the ability of C. japonica to form traumatic resin canals, it was likely that the shorter feeding period was the most important factor in enabling E. granitalis to escape from mortality by host oleoresin.