Abstract: 【Aim】 This study aims to determine the size variation of adults and the overwintering larvae of the Japanese pine sawyer, Monochamus alternatus, and to explore the relationship of the body size of adults and the body weight of overwintering larvae of this species. 【Methods】 Field trapping of M. alternatus adults was carried out from 1st May to 31st October in 2014 in forests of Changdong, Fuyang County in Zhejiang Province, and the body length and width of adults trapped were measured with micrometer to determine the size variation. Overwintering larvae were collected also in Changdong forests in March 2014 and then taken back to the laboratory and reared with artificial diet until adult emergence, during which the weight and width of head capsule of larvae, pupal weight and adult size were recorded to analyze the relationship between the size variations of adults and the overwintering larvae. 【Results】 Trapped M. alternatus adults varied in body size. The body length and width of female adults averaged 20.59±0.19 and 6.59±0.06 mm, respectively, while those of male adults averaged 19.90±0.26 and 6.44±0.08 mm, respectively. Female adults were significantly longer than males. Furthermore, body length was significantly correlated with body width for both female and male adults. The investigation of overwintering larvae showed that M. alternatus larvae overwinter mainly at the 4th and 5th instar by measuring the width of head capsule, which ranged from 2.20 to 4.24 mm, and larval body size also varied, ranging from 71.6 to 858.0 mg with the average of 304.2 mg among which the 5th instar overwintering larvae was significantly heavier than the 4th instar overwintering larvae. Further analysis showed that the size of pupae and adults was determined by the size of overwintering larvae. Regression analysis showed that the pupal weight, adult weight, adult length, and adult width were significantly correlated with the overwintering larval weight, respectively. Pupae and adults reared from the 4th instar overwintering larvae were significantly lighter than those reared from the 5th instar overwintering larvae. 【Conclusion】 The body size of M. alternatus adults is quite varied, which is related to the size variation of overwintering larvae. Variation in larval size may be attributed to the long flight period of adults. Oviposition lasts the whole flight period, causing the difference in larval development time, and this difference as well as nutrition difference in different parts of host pine trees results in the variation in larval body size until overwintering.

Key words: Monochamus alternatus, adult, overwintering larvae, body size, body weight, regression analysis