Changes In Juvenile Hormone Level And Vitellogenin Gene Expression In Reticulitermes Labialis During The Development Of Adultoid Reproductives And Brachypterous Neotenic Reproductives From Last Instar Nymphs

The plasticity and diversity of secondary reproductives play important roles in the survival and expansion of termite colonies. Secondary reproductives are primarily differentiated from nymphs.The last-instar nymphs can transform into adult reproductives (AR) and brachypterous neotenics (BN). However, the differentiation and development of AR and BN from last instar nymphs have been rarely reporteded, because of AR contain wings when moulting. Some researchs reported it come from alate in Kalotermitidae and Termitidae, while reported it as neotenic in Reticulitermes(Rhinotermitidae). So some people regard it as alate, while some take it as neotenics. In particular, the origin of AR remains a mystery, and the adjustment mechanism during the differentiation and development of AR has not been reported. In this study, the juvenile hormoneⅢ (JH) level and vitellogenin gene expression of last instar nymphs of Reticulitermes labralis that differentiated and developed into AR or BN as well as the oogenesis of AR and BN in the first spawning cycle were investigated. The results were showed as followings:1. The adults originated from the last instar nymphs by moulting, but not from the alate adults and ARs were not able to survival and create new nests without workers. ARs were more similar to neotenic reproductives in morphology and in behaviour. The group size affect differentiation time of reproductive from last nymphs.2. The JH level of the last instar nymphs five days after the separation from their natural colony rapidly increased to 1.45±0.18 ng/mg; one week later, when the last instar nymphs moulted and differentiated to AR or BN, the JH level declined to 0.42±0.12 ng/mg and 0.69± 0.32 ng/mg, respectively. The JH level of the adults reached its highest value of 1.42±0.52 ng/mg at day ten after moulting, whereas that of BN reached its maximum value of 1.31±0.24 ng/mg at day five, the last instar nymphs need higher JH level to differentiated to BN than differentiated to AR. Which indicated that to differentiate into reproductives after moulting, the last instar nymphs required dramatically increased JH titres during the differentiation process of the last instar nymphs to AR and BN, the JH titre assumed the same dynamic trend of initially increasing and then decreasing. The level of JH influenced the conversion direction of last instar nymphs to various reproductives.3. After five days of isolated culture, the vitellogenin gene expression level of last instar nymphs increased rapidly to 0.2640±0.1848, which was 26 times greater than that of last instar nymphs before the isolation. When last instar nymphs moulted and differentiated to AR or BN, the vitellogenin gene expression levels decreased to their lowest levels of 0.0036±0.0015 and 0.0358±0.0269, respectively, with the vitellogenin gene expression level of BN was approximately ten times that of the adults. The vitellogenin gene expression level of BN and AR all displayed the same dynamic change of increasing at first and then declining, and they both reached their peak values of 0.3956±0.0787 and 0.6811±0.1215, respectively, at day 15, and declined thereafter until spawning. In the process of development and maturation of oocytes, the vitellogenin gene expression level of BN was always higher than that of the AR, and the oocytes of BN matured earlier than those of the AR. The increase of JH level was earlier that the increase of vitellogenin gene expression level, which indicated the vitellogenin gene expression level was regulated by JH level, and the JH titre was the deciding factor of the initiation and continuation of vitellogenesis. The difference between the time required for adults and BN to reach the peak JH titre was the key factor in the timing of oocyte maturation and spawning between the two termite reproductives.4. The oocytes of BN matured earlier than those of the AR. The vitellogenic oocytes appeared in the ovaries of adults at day 15 and reached mid-vitellogenesis stage at day 20 after moulting, whereas the vitellogenic oocytes appeared in the ovaries of BN at day 10 and reached the late stage of vitellogenesis at day 20. The number of vitellogenic oocytes and initial fecundity of the BN were higher than that of the AR, and the BN also spawned earlier than did the adults.The initial fecundity of BN at 2.7±0.6 (n= 5) and of AR at 1.3±0.5 (n= 5) and the earliest initial spawning time of the BN and was 24.7±2.6 (n= 5)and 28.5±2.2. AR spawninged less eggs than BN in the beginning colony, in 10 months there was no significant difference between the number of offspring between AR and BN. AR can increase the fertility of nest in a short time can, ensure the colony expansion and development in termite.