a1 Department of Insect Physiology and Behavior, National Institute of Sericultural and Entomological Science, Ohwashi 1–2, Tsukuba, Ibaraki 305, Japan
a2 Crops Laboratory, Okinawa Prefectural Agricultural Experimental Station, Miyako Branch, 2071–40, Nishizato, Horara, Okinawa 906, Japan
The role of photoperiod in controlling the termination of adult diapause in the Bombay locust, Nomadacris succincta Linnaeus (formerly Patanga succincta) was examined by exposing pairs of field-collected adults to different photoperiods at 30°C. Adults of this species appear in June and remain in diapause until March in the following spring. Female adults collected in November started laying eggs earlier at a 14 h photoperiod (L:D 14:10) than at a 12 h photoperiod (L:D 12:12), although the mean pre-ovipositional periods at the two photoperiods were not significantly different from each other. All first egg-pods produced by long-day females contained fertilized eggs while only some short-day pairs produced fertilized eggs in their first pod, indicating that mating was suppressed at a short photoperiod. In adults collected in January and exposed to a 10 h photoperiod (L:D 10:14), the mean time of first oviposition was significantly delayed compared to those exposed to a 14 h photoperiod. These results demonstrate that N. succincta uses daylength as a cue to control the time of diapause termination in the field. The time interval between the first and second egg-pod depositions was influenced not only by the physiological state of the females but also by the environmental conditions, i.e. photoperiod, and it was positively correlated with the length of pre-ovipositional period. The occurrence of a change in host preference by diapause adults and its ecological significance were also pointed out.
(Accepted February 16 1997)