Acta Entomologica Sinica ›› 2020, Vol. 63 ›› Issue (4): 512-522.doi: 10.16380/j.kcxb.2020.04.014

• RESEARCH PAPERS • Previous Articles     Next Articles

Determination of larval instars and the observation of head morphology and sensilla of the final instar larva of Callosobruchus chinensis (Coleoptera: Bruchidae)

CUI Xiao-Lin1, WANG Hong-Min2, ZHANG Jing1, ZHANG Xian-Hong1, ZHENG Hai-Xia1,*   

  1. (1. College of Agriculture, Shanxi Agricultural University, Taigu, Shanxi 030801, China; 2. College of Economics and Management, Shanxi Agricultural University, Taigu, Shanxi 030801, China)
  • Online:2020-04-20 Published:2020-05-08

Abstract: 【Aim】 This study aims to clarify the number of larval instars and to understand the types, morphology and distribution of sensilla on the final instar larval head of the adzuki bean beetle, Callosobruchus chinensis. 【Methods】 The body length, head capsule 
width and mandible width of C. chinensis larvae were measured. Based on the frequency histograms, regression relationship and Dyar’s rule of the obtained data, the optimal morphological index for determining the larval instars of C. chinensis was determined. The obtained result was verified by Crosby growth rule and linear regression method. The morphology and sensilla on the head of the final instar larva of C. chinensis were observed under scanning electron microscope. 【Results】 The frequency histograms of the body length, head capsule width and mandible width of C. chinensis larvae showed four obvious peaks, and it is so inferred that C. chinensis larvae have four instars. The four instars had the body length range of 1.581-2.556, 2.406-3.381, 3.381-4.281 and 4.206-4.881 mm, the head capsule width range of 0.444-0.689, 0.654-0.934, 0.934-1.179 and 1.144-1.389 mm, and the mandible width range of 0.080-0.256, 0.234-0.344, 0.322-0.542 and 0.542-0.652 mm, respectively. The body length, head capsule width and mandible width are in accordance with Dyar’s rule and Crosby growth rule, and show obvious linear relationship. Therefore, the body length, head capsule width and mandible width can be used as important indexes for the division of larval instars of C. chinensis. The Crosby ratio of head capsule width is smaller than those of body length and mandible width, and the correlation coefficient between the logarithmic value of head capsule width and body length and larval instar is higher than that between mandible width and larval instar, so the head capsule width can be used as the optimal index for the division of larval instars. Seven types of sensilla including sensillum basiconicum, sensillum trichodeum, sensillum lageniform, sensillum chaeticum, sensillum placodeum, sensillum styloconicum and sensillum ampullaceum were observed on the head and are mainly located on the antennae, maxillary palp, labrum and mandible. 【Conclusion】 The morphological indexes of the division of larval instars and the observation of head morphology and of the C. chinensis provide a theoretical basis for the study of behavior and integrated control.

Key words: Callosobruchus chinensis, larval instars, body length, head capsule width; mandible width, sensilla