Photoperiodic induction of prepupal diapause and its role in synchronization with host phenology in the hibiscus caterpillar, Xanthodes transversa

The hibiscus caterpillar, Xanthodes transversa (Lepidoptera: Noctuidae), is a multivoltine insect that is an important pest of Malvaceae plants such as the okra, Abelmoschus esculentus, and the common rose mallow, Hibiscus mutabilis, in Japan. In the present study, the effects of photoperiod and temperature on the induction of prepupal diapause and the adaptive significance of this diapause were examined in a local population of X.transversa in Miyazaki, Kyushu, southwestern Japan. Larvae showed a long-day photoperiodic response for controlling the induction of prepupal diapause with a critical day length between 13 and 14h at 20 to 25 degrees C. Under long-day conditions larvae rapidly pupated from the sixth instar, but under short-day conditions they entered diapause in the prepupal stage. Diapause occurrence in the field increased in late September, which was consistent with the laboratory results in terms of the photoperiodic response. Non-diapause development after this time is maladaptive because most larvae of the next generation could not reach the critical stage (prepupae) before winter and died during early winter in outdoor experiments. Larvae suffered from a high rate of mortality when fed leaves collected late in autumn. The photoperiodic response for controlling the induction of diapause in this insect may play an important role in synchronizing the life cycle with the seasonal changes in food and temperature conditions.