Abstract
The predatory thrips Haplothrips brevitubus (Karny) is expected to be used as a biological control agent against pest thrips in greenhouses. To clarify the effect of photoperiod on induction of reproductive diapause in this species and its geographic variation, females from Iwate (39.5°N), Kyoto (35.5°N), and Kagoshima (31.5°N) populations were reared under six different photoperiodic conditions at 20°C. Females reared under a long-day condition (16L8D) initiated oviposition within 15 days after adult emergence, while those reared under short-day conditions entered reproductive diapause. The critical day-length for induction of the diapause was about 15 hours in the Iwate population, between 14 and 15 hours in the Kyoto population, and between 12 and 13 hours in Kagoshima population. Although the maximum percentage of diapausing females below the critical day-length was more than 90% in Iwate and Kyoto populations, it was less than 50% in the Kagoshima population. Variation in photoperiodic response curves for diapause induction among several bloods within the Kagoshima population was larger than that in Iwate and Kyoto populations. Moreover, mean pre-oviposition period of females entering diapause in the Kagoshima population was shorter than that in Iwate and Kyoto populations. The critical day-lengths for diapause induction in reciprocal crosses between Kyoto and Kagoshima populations were between 13 and 14 hours, and the incidence of diapause in the crosses was higher than that of the Kagoshima population under a short-day length (<14L).
