Photoperiodic Regulation of Seasonal Diapause Induction in the Field Bindweed Moth, Tyta luctuosa (Lepidoptera: Noctuidae)

Field and laboratory experiments were conducted to determine the influence of photoperiod on diapause induction in an Italian population of the moth Tyta luctuosa (Denis and Schiffermuller), which has been released as a potential biological control agent of field bindweed in North America. In the laboratory, the percentage of pupae that entered diapause at 25°C was related inversely to photoperiod. Most, and possibly all, instars were sensitive to photoperiod. Sensitivity increased as a function of both the larval stage of development and the duration of exposure to diapause-inducing short day lengths. Soil-inhabiting, late fifth instars and pupae did not respond to photoperiod. All insects underwent diapause when reared in the laboratory at 13.5:10.5 (L:D) h. The critical photoperiod (50% diapause) was estimated to be between L:D 15:9 and 15.5:8.5 h. About 20% of T. luctuosa entered diapause under the longest day length (16:8 [L:D] h), indicating a strong tendency for diapause in this population. When T. luctuosa was field-reared under natural day lengths and temperatures, a variable but generally high percentage underwent diapause from spring to late summer. Under the shorter day lengths of August and early September, most of the insects entered diapause and the variation was lower. A variable diapause response may represent an adaptation to periods of unpredictable bindweed quality during summers in southern Europe. Our findings have immediate utility for developing mass-rearing and release strategies for T. luctuosa. In addition, they will allow better predictions of its phenology and population dynamics if this species becomes established in North America.