Development of the head capsule of Hyphantria cunea larvae
Author of the article:LONG Dan1, 2** LIU Le1** WEI Yi-Tong1 DANG Ying-Qiao1 SONG Xue-Yu1, 3 WANG Xiao-Yi1***
Author's Workplace：1. Ecology and Nature Conservation Institute, Chinese Academy of Forestry, Beijing 100091, China; 2. Chinese Academy of Forestry, Beijing 100091, China; 3. Anhui Academy of Forestry, Hefei 230031, China
Key Words：Dyar’s law; head capsule width; temperature; photoperiod; starvation stress; host plant
Abstract：[Aim] To clarify the applicability and stability of head capsule width (HCW) as a parameter for instar identification in Hyphantria cunea. [Methods] Growth patterns of larval HCW were measured and the effects of various environmental conditions on HCW development were investigated. Temporal and instar-specific changes in HCW were observed under controlled laboratory conditions. In addition, differences for head capsule development under various diet type, food consumption, temperature, and photoperiod were also recorded. [Results] With increasing age in days, the HCW of H. cunea larvae had a typical exponential growth trend (R2 = 0.961 2). Validation using Crosby’s growth rule and linear regression analysis confirmed significant differences in HCW between successive instars (P < 0.001). An exponential relationship was observed between instar number and HCW (R2 = 0.995 3), confirming its validity as a parameter for instar determination. Diet type significantly affected the HCW of 3rd to 6th instar larvae (P < 0.05), whereas food consumption had no significant effect. Temperature significantly influenced HCW from the 2nd instar onward; notably, HCW at 20 ℃ was significantly narrower than at higher temperatures (P < 0.05). With the exception of the 4th and 6th instars, larvae reared under long-day conditions possessed significantly wider HCW than those reared under short-day conditions (P < 0.05). [Conclusion] HCW is a suitable parameter for instar identification in H. cunea. However, environmental factors such as diet, temperature, and photoperiod influence head capsule development to varying degrees. Therefore, when applying Dyar’s Law for instar determination in the field, larvae should be sampled from the same environmental conditions to ensure accurate instar identification.