Juvenile hormone regulates the shift from migrants to residents in adult oriental armyworm, Mythimna separata

Authors: ZHANG, LEI - Chinese Academy Of Agricultural Sciences; CHENG, LILI - Chinese Academy Of Agricultural Sciences; CHAPMAN, JASON - University Of Exeter; Sappington, Thomas; LIU, JUANJUAN - Chinese Academy Of Agricultural Sciences; CHENG, YUNXIA - Chinese Academy Of Agricultural Sciences; JIANG, XINGFU - Chinese Academy Of Agricultural Sciences

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2020
Publication Date: 7/15/2020
Citation: Zhang, L., Cheng, L., Chapman, J.W., Sappington, T.W., Liu, J., Cheng, Y., Jiang, X. 2020. Juvenile hormone regulates the shift from migrants to residents in adult oriental armyworm, Mythimna separata. Scientific Reports. 10.Article 11626. https://doi.org/10.1038/s41598-020-66973-z.
DOI: https://doi.org/10.1038/s41598-020-66973-z

Interpretive Summary: The oriental armyworm, Mythimna separata, is one of the most important pests of corn in Asia. Like many closely-related pests of corn in the U.S., including the sister armyworm species Mythimna unipuncta, it overwinters in the south and migrates long distances to northern regions in the spring. After arrival, the migrant adults lay eggs in corn and other crops, after which larvae hatch and damage the plants. However, not all oriental armyworm adults that emerge in the south migrate; some stay as residents to lay eggs in nearby fields. How the decision is made to remain a resident or to become a migrant is important to know when predicting migratory activity and timing of arrival in the north. A previous study showed that the decision to remain or migrate, and the physiological changes associated with the two alternatives, are made during the larval stage, but that adverse environmental conditions during a sensitive period in adulthood switches migrants into residents. In this study, the biochemical mechanism controlling the switch from migrant to resident was investigated. The results suggest that increased rate of juvenile hormone (JH) release on the first day of adulthood is the likely mechanism. Experiments where a JH mimic was applied to migrant adults during this sensitive stage accelerated and enhanced reproduction, while reducing flight muscle mass and flight activity. These results will be of interest to government and university scientists studying the physiology and population dynamics of migratory insect pests.

Technical Abstract: In migratory insects, increasing evidence has demonstrated juvenile hormone (JH) is involved in regulating adult reproduction and flight. Our previous study demonstrated that migrant Mythimna separata were induced to switch into residents by adverse environmental stimulation during a sensitive period in adulthood which be called “the secondary regulation of migration”, but the mechanism of JH regulating the switching from migrants to residents is not clear. We found a significantly different pattern of JH titers between migrants and residents, with migrants showing slower release of JH during adulthood than residents. Application of JH analogue (JHA) during day 1 after emergence, representing a sensitive stage for migrants shifting to residents, significantly accelerated adults reproduction but suppressed flight. The pre-oviposition period (POP) and period of first oviposition (PFO) of migrants treated with JHA significantly decreased, while the total lifetime fecundity, mating percentage increased significantly. Flight capacity and dorso-longitudinal muscle size also decreased significantly in migrants treated with JHA. These changes promoting reproduction but reducing flight by JHA resulted in the shifting of migrants to residents. These results, combined with those of our previous study, suggest a role for JH in regulating the phase change from migrants to residents during a sensitive stage.