Reproductive system development in Monochamus alternatus hope subjected to maturation feeding

Monochamus alternatus Hope (Coleoptera: Cerambycidae), a vector of the invasive pathogenic nematode Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle, is a notorious forest pest in Asia. After emergence, adult M. alternatus must supplement nutrition to further develop and reach sexual maturity before they can engage in courtship and mating. However, there is a lack of information on the precopulation duration of the Chinese population of M. alternatus and the reproductive system development of both sexes subjected to maturation feeding. In this study, we investigated the precopulation duration and the dynamic changes of testes, ovaries, bursa copulatrix, and spermatheca. Our results showed that no copulation behavior was observed during the first 3 d, and all adults completed the first copulation on the tenth day after emergence, suggesting that the precopulation duration ranges from 4 to 10 d. During the precopulation duration, the testicular color gradually changed from translucent to milky-white opaque, and a total of 6 cell types were identified in the testes. However, no significant differences in testicular diameter were observed from the first to the tenth day. Ovaries underwent obvious changes starting on the third day postemergence. Furthermore, no external morphological changes were observed in the bursa copulatrix and spermatheca, specifically, bursa copulatrix length showed no significant difference from the first to the tenth day postemergence. Understanding this information provides valuable insights into the reproductive biology of M. alternatus, with significant implications for monitoring its field performance and developing effective control strategies for both this pest and pine wilt disease.