Abstract: Ectropis grisescens is one of the most harmful pests in tea plantations, characterized by its frequent annual occurrences and considerable damage. The understanding of the larval instar number remains still elusive. To clarify the relationship between the larval instars of Ectropis grisescens and temperature, the differences in larval instar and the fertility indexes including developmental duration, pupal weight and sex ratio of different larval instar populations were measured at five different temperatures ( 21, 23, 25, 27, 29 ℃) in the climate incubators. The results show that the E. grisescens were 4 (molting 3 times, referred to as the 4th instar) or 5 (molting 4 times, referred to as the 5th instar) larval instars at each temperature from 21 ℃ to 29 ℃. At 21 ℃ and 23 ℃, there was no significant differences between the proportion of 5th instar and 4th instar. When the temperature exceeded 25 ℃, the proportion of 5th instar was significantly higher than that of 4th instar, reaching 67.4%-78.6%. Temperature had a significant effect on the developmental duration, pupal weight of the 5th and 4th instars, but had no significant effect on the sex ratio of male and female. At the same temperature, the larval period of the 5th instar was longer than the 4th instar, the pupal weight increased, and the sex ratio increased significantly. This study indicates that the larval instars of E. grisescens were 4 or 5, and the proportion of 5th instar larvae increased with the increase of temperature. This may be a survival strategy of E. grisescens to deal with adverse environment.

Key words: Ectropis grisescens, instar number, temperature, developmental duration, pupal weight, sex ratio