Abstract: 【Aim】 This study aims to explore the characteristics of embryonic development between gamogenesis and parthenogenesis in Reticulitermes. 【Methods】 Fertilized eggs (female-male paired eggs, FM eggs) and unfertilized eggs (female-female paired eggs, FF eggs) were used for observing egg cleavage in two termite species, Reticulitermes chinensis and R. aculabialis. We used laser scanning confocal microscope for egg cleavage observation and digital microscope for observing external morphology of eggs and embryos. 【Results】 Fertilized and unfertilized eggs from queens of R. chinensis could all cleave in the nest. Comparison between the nuclei of FF and FM eggs in 24 and 48 h revealed no significant difference in the number of nuclei for FF egg, but significant difference for FM egg. On the 15th day of egg development, no significant changes occurred in the volume of FF egg, whereas the volume of FM egg significantly increased. The FF eggs died on the 15th-20th day, while the FM eggs were in normal development. There was no significant difference in the number of nuclei in the same period between the fertilized and unfertilized eggs of R. aculabialis, and the number of nuclei in 48 h was significantly more than that in 24 h. The length and width of the fertilized eggs significantly changed on the 10th day, with the volume significantly increasing at the same time. The increase of length, width and volume of unfertilized eggs, however, occurred on the 15th day. 【Conclusion】 The fertilized eggs and unfertilized eggs of facultative parthenogenesis R. aculabialis have the same cleavage rate. But the change in the shape of the fertilized eggs is earlier than that of the unfertilized eggs. Unfertilized eggs of R. chinensis can cleave, but have abnormal development, and can not hatch in the end. The length and width of eggs of these two termite species change simultaneously in the same development stage. The cleavage characteristics of FF egg of R. chinensis may be a preadaptive stage from bisexual reproduction to facultative parthenogenesis in termite reproductive evolution.

Key words: Reticulitermes; Reticulitermes chinensis, Reticulitermes aculabialis, embryonic development, parthenogenesis, reproductive evolution, egg cleavage