Abstract: 【Aim】 Ficus pumila. var. pumila is not only a key tree species of tropical and subtropical plant ecosystems, but also an important tree species of urban vertical greening. Wiebesia pumilae is the obligate pollinator of F. pumila var. pumila. Fig wasp larvae live in the gall of syconium for a long time, with special features of small body, long stadium, and difficulty for observation. The purpose of this study is to establish the classification criteria of larval instars of fig wasps, and to explore a reliable method for determining the number and stadia of larval instars of recessive insect larvae. 【Methods】 A total of 447 larvae of W.pumilae at different developmental stages were collected, and the morphological indicators including head capsule width, width of the 3rd segment, body length and girth were measured. The larval instars were determined by frequency distribution method, and the larval stadia were calculated by the population median stadium measurement method. 【Results】 The frequency distribution of larval head capsule width, width of the 3rd segment, body length and girth all showed five peaks, suggesting that there are five larval instars. Since the coefficient of variation in the width of the 3rd segment was greater than 20%, it was not suitable as the index of instar division. Regression analysis showed that the head capsule width, body length and girth were extremely significantly correlated with the larval instars (P<0.01). Because the coefficient of determination (R²) of regression curve for body length measurement and larval instars was the highest, the body length was the optimal measurement index of instars, and the regression equation was y=0.14^e0.55x(P＜0.01, R²=0.97). The stadia of the 1st-5th instar larva of W. pumilae was 429, 13.19, 6.27, 24.46 and 8.90 d, respectively, and the total larval stadium was 57.11 d. 【Conclusion】 This study determined the number and stadia of larval instars of W. pumilae and screened out the optimal age index of larval fig wasps, providing a foundation for studying fig-wasp co-evolution.

Key words: Wiebesia pumilae, pollinator, larva, head capsule width, body length, frequency distribution method