The Significance of Embryonic Diapause in a Japanese Strain of the Migratory Locust, Locusta migratoria (Orthoptera, Acrididae)

Effects of temperature on induction, maintenance and termination of embryonic diapause in a Japanese strain of the migratory locust, Locusta migratoria L., were studied by exposing eggs to laboratory and outdoor conditions. Embryonic development at different temperatures was assessed by measuring the antennal length. This method proved to be useful in distinguishing diapausing embryos from non-diapausing ones. Incubation temperature influenced the onset of diapause in eggs maternally destined to diapause, and embryos were most sensitive to temperature during a period shortly before the diapause stage. The thermal optimum for diapause development fell in the range from 10 to 12.5℃. Diapausing eggs responded to constant and fluctuating temperatures in different ways. During the early stage of diapause development, exposure of eggs to a moderately high temperature cancelled or suppressed the diapause-terminating action of low temperature. This effect was clearly detected by final incubation at 20℃ but not at 25℃. The significance of such responses was discussed in relation to the temperature conditions to which eggs of this species were exposed in nature. Eggs deposited late in the season failed to attain the diapause stage before winter arrived. Yet, many could overwinter and hatch in the following spring, indicating that diapause is not a prerequisite for overwintering in L. migratoria.