Adult diapause in Riptortus clavatus (Thunberg) was induced by short-day photoperiods, and the critical daylength for its induction was 13.5 h. When insects were reared from eggs under diapause-inducing photoperiods near the critical daylength, the duration of diapause was shorter than when reared under the shorter daylengths. Adults terminated diapause under long-day photoperiods earlier when they had been raised under a near-critical photoperiod than under shorter daylengths; this indicated that the initial intensity of diapause was dependent on the length of the inducing photoperiod. Not only the photoperiods experienced during preimaginal development but also the value of the long-day photoperiods experienced after adult emergence affected the time of onset of oviposition. When the photophase was shortened, either abruptly or gradually after adult emergence, the duration of diapause was prolonged. Diapause was long when induced by shorter daylengths than the near-critical photoperiod. Different photoperiods have thus different quantitative effects on both the initial intensity of diapause and the rate of diapause development.
The receptor for photoperiodism in nymphs of Poecilocoris lewisi was examined using a phosphorescent paint, which absorbs light energy and emits phosphorescence in the dark. This species shows a facultative diapause in the fifth (final) nymphal instar and its induction is primarily controlled by photoperiod in the fourth instar. The incidence of diapause in the fifth instar was determined after exposing selected regions of the body surface to a longer photophase than the rest by applying a phosphorescent paint in the fourth instar. The incidence of diapause was significantly lower in insects with their compound eyes painted than in control insects at near-critical daylengths. However, painting the central part of the head had no effect. It is concluded, therefore, that the compound eyes are the principal receptor for photoperiodism in nymphs of P. lewisi. This is the first report implicating the compound eyes in the reception of photoperiod in nymphal insects.
Photoperiodic responses and their adaptive significance were examined in Riptortus clavatus (Heteroptera: Alydidae), Plautia crossota stali, Dolycoris baccarum, Aelia fieberi, Nezara viridula, Nezara antennata, Graphosoma rubrolineatum, Dybowskyia reticulata, and Eurydema rugosum (Heteroptera: Pentatomidae) in the Kyoto-Osaka area, central Japan. All of these species overwinter as adults in diapause. Although they have similar feeding habits, their photoperiodic responses were quite different. Riptortus clavatus, P. c. stali, D. baccarum and N. viridula showed long-day photoperiodic responses with critical daylengths between 13 and 14 h, and were assumed to have three generations per year. The photoperiodic responses of the other five species were different both from those of the above species and from each other. These results suggested that A. fieberi and N. antennata produce two generations per year, and G. rubrolineatum, D. reticulata and E. rugosum have one or two generations per year. Nezara antennata showed a long-day-short-day photoperiodic response with summer adult diapause, which may avoid production of heat-susceptible nymphs in the hottest season. With the exception of N. antennata, the photoperiodic responses resulting in fewer generations were shown to be adaptations to dietary conditions in the field.