Abstract: Leptocybe invasa is an invasive pest, native to Australia, which causes serious damage to Eucalyptus all over the world. Here, we monitored gall development in resistant and susceptible Eucalyptus clones to determine whether plant genotype affects the durations of the different gall stages. Gall development varied among six Eucalyptus clones that differed in susceptibility to L. invasa viz., PE-5, 316, 3011, PE-11, 3020 and P-13 in Punjab in a nethouse. In susceptible clones PE-5 and 316, L. invasa emerged from both green and pink galls. Five stages of gall formation were found: Stage 1 (tissue disruption), Stage 2 (gall development), Stage 3 (glossy pink), Stage 4 (dull pink) and Stage 5 (exit hole) in susceptible clones when adults emerged from pink galls. However, in resistant clones, adults emerged only from green galls, and galls formed in three stages. In the susceptible clones, when adults emerged from pink galls, the life cycle was 105–115 d; however, when adults emerged from green galls, the duration was significantly shorter (81–87 d). In the most-resistant clone, P-13, corky tissue formed after oviposition, and galls did not develop further. In the resistant clones (3020, PE-11 and 3011), adults emerged from green galls, and the life cycle lasted 90–96 d. When adults emerged from green galls in susceptible and resistant clones, Stage 1 lasted longer in resistant clones than in the susceptible; however, in susceptible clones, Stage 5 was longer. When adults emerged from pink galls in susceptible clones and from green galls in resistant clones, the life cycle was longer in susceptible clones. In susceptible clones, the number of emergence holes was significantly higher than resistant clones. Gall width and gall length also differed significantly between susceptible and resistant clones. The results showed that the Eucalyptus genotype had a significant effect on gall development induced by gall wasps.

Key words: Eucalyptus, Leptocybe invasa, Gall development, Resistant genotype, Susceptible genotype