Characteristics related to pine gall midge attack in resistant or susceptible pinus thunbergii and pinus densiflora

During the period 1975~80, 211 Japanese black pines (Pinus thunbergii) and 155 Korean red pines (Pinus densiflora) were selected as phenotypically resistant to pine gall midge (Thecodiplosis japonensis) throughout the country. Resistant and susceptible types of both species did not differ significantly in most of the traits examined. However, resin duct number was consistently greater in resistant types than in susceptible types. In the resistant trees, resin-like substances secreted in the needles by the stimulation of insect attack appear to play a preventing role in further larval feeding. Thus, larvae were isolated fro m the inner tissue of the needle leading to death. Tryptophan, a precursor of IAA, was detected in larvae of the pine gall midge and also in gall tissues, indicating that a growth substance is involved in gall formation.