Effects of Juvenile Hormone Analog and Days after Emergence on the Reproduction of Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae) Populations.

Mythimna separata (Walker) is a main cereal crop pest that causes extensive damage to the world grain production. The effects of juvenile hormone on M. separata populations remain poorly understood. Here, we explored how JH analog (JHA) affected reproductive traits of both migrant and resident populations in this pest. Our results showed that the influence of JHA treatment on reproduction depended on adult age (days after emergence) of exposure to JHA and populations. Exposure of M. separata residents to JHA (methoprene) on day 1 and day 2 after adult emergence significantly shortened the pre-oviposition period, but increased the lifetime fecundity, mating frequency and grade of ovarian development compared to the controls. However, M. separata migrants exposed to JHA only on day 1 facilitated their reproduction, resulting in a reduction in the pre-oviposition period but an increase in lifetime fecundity, mating frequency and grade of ovarian development. In addition, exposure to JHA from day 2 to day 4 did not significantly affect the ovarian and reproductive development in both migrant and resident populations. These results indicated that the first two days after adult emergence were the sensitive period for residents. In contrast, only the first day after adult emergence was the sensitive stage for migrants. Our findings will contribute to a better understanding of JHA function on M. separata populations.