PHOTOPERIODIC CONTROL OF LARVAL DEVELOPMENT IN THE SEMIVOLTINE COCKROACH PERIPLANETA-JAPONICA (BLATTIDAE, DICTYOPTERA)

Periplaneta japonica is semivoltine, entering early diapause in any (e xcept the first) larval instar before the last, and late diapause in t he last instar. Early diapause was induced under a short day of 13 h o r less at 28-degrees-C, and under both short and long daylength (12-16 h) at 20-degrees-C. The shorter the daylength and the lower the tempe rature, the younger the instar was entering early diapause. Early diap ause was terminated by a long day (16 h) or a high temperature (28-deg rees-C), after which larvae grew faster in short days than in long day s until the last instar, when they again entered diapause, always in s hort days and frequently in long days. This late diapause was terminat ed also by an increase in daylength and was always followed by adult e mergence. In this case, 13 and 14 h daylengths after exposure to 12 h daylength were as effective as 16 h daylength. Outdoor samples collect ed in late autumn, winter and early spring at Hirosaki (40.5-degrees-N ) comprised two distinct size groups, corresponding with the early and late diapause instars. Based on these results, the seasonal developme nt strategy and intriguing aspects of the photoperiodic response in th is cockroach are discussed.