关键词: 油茶象, 头壳宽, 头壳长, 上颚宽, 频次分布, 多峰拟合, 戴氏法则

Abstract: 【Aim】 The camellia weevil, Curculio chinensis Chevrolat, is an important pest of the fruits of oil tea camellia ( Camellia spp.) in China. Its infestation often leads to a lot of fruit drop from the camellia plants. For the study of the biology and ecology of weevil, it is very important to be able to determine the instar of the larva. However, in the case of xylophagous insects, this is particularly difficult. This study aims to clarify the number of larval instars of this pest, to identify the ranges of the instars in our study area and to design a reliable method for determining the instars of an individual larva. 【Methods】 In 2014, 1 253 larvae of  C. chinensis were collected from Camellia meiocarpa, and the head capsule width and length, and the mandible width of each larva were measured. Frequency distribution of the data was fitted using multiple peak fit (in Origin 9.0), the separation points of adjacent instars were determined by the intersection points of the normal curve, and then the means, range, growth ratio, and misclassification probability for all larval instars of the weevil were calculated. For the determination of the instar number, the Dyar’s rule was also used. 【Results】 Multiple peak fit of the frequency distribution of the head capsule data resulted in 5 normal and distinct peaks (P＜0.01), representing the five instars (1st-5th instars). The misclassification probability of the 3rd instar larva was 6.04%, 7.03% and 6.51% for the head capsule width, head capsule length and mandible width, respectively. The misclassification probability of the other instars was less than 5%, suggesting that the 3 morphological measurements could be used to identify the weevil’s larval instars, of which the head capsule width is the most important one. The growth ratios of the instars were almost constant, being 1.41-1.54, 1.43-1.61 and 1.44-1.64 for head capsule width, head capsule length and mandible width, respectively. The positive correlation between the natural logarithm of the measurements and the larval instars showed that the larval growth of the weevil followed Dyar’s rule of a geometrical growth pattern. 【Conclusion】 The camellia weevil has 5 instars instead of the 4 instars found in the previous research. Multiple peak fit is useful to determine the instar number of xylophagous insects or field collected larvae. Especially, it provides an effective method to identify the number of larval instars despite the overlap of adjacent instars.

Key words: Curculio chinensis, head capsule width, head capsule length, mandible width, frequency distribution, multiple peak fit, Dyar’s rule