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 T yta luctuosa (Denis and Schiffermuller), which has been released as a poten tial biological control agent of field bindweed in North America. In the la boratory, the percentage of pupae that entered diapause at 25 degrees C was related inversely to photoperiod. Most, and possibly all, instars were sen sitive to photoperiod. Sensitivity increased as a function of both the larv al stage of development and the duration of exposure to diapause-inducing s hort day lengths. Soil-inhabiting, late fifth instars and pupae did not res pond to photoperiod. All insects underwent diapause when reared in the labo ratory at 13.5:10.5 (L:D) h. The critical photoperiod (50% diapause) was es timated to be between L:D 15:9 and 15.5:8.5 h. About 20% of T. luctuosa ent ered diapause under the longest day length (16:8 [L:D] h), indicating a str ong tendency for diapause in this population. When T. luctuosa was field-re ared under natural day lengths and temperatures, a variable but generally h igh percentage underwent diapause from spring to late summer. Under the sho rter day lengths of August and early September, most of the insects entered diapause and the variation was lower. A variable diapause response may rep resent an adaptation to periods of unpredictable bindweed quality during su mmers in southern Europe. Our findings have immediate utility for developin g mass-rearing and release strategies for T. luctuosa. In addition, they wi ll allow better predictions of its phenology and population dynamics if thi s species becomes established in North America. (C) 2000 Academic Press.