Diapause induction in a Kentucky population of Diprion similis (Hymenoptera: Diprionidae).
Critical photoperiod, sensitive stage for diapause induction, and requirements for termination of diapause were studied in a colony of the introduced pine sawfly, Diprion similis, established from a wild Kentucky population. The induction of diapause was studied in the laboratory under photoperiods (LD) of 10:14, 11:13, 12:12, 13:11, 14:10, 15:9, and 16:8 in the first trial, with a photoperiod of 9:15 added in the second trial. Individuals exposed to light periods ≤ 12:12 entered diapause and individuals in a photoperiod >13:11 bypassed diapause. The sensitive stage was determined using reciprocal switches of diapause-inducing (9:15) and non-diapause inducing (16:8) regimes. These studies indicated that late instars of the introduced pine sawfly are significantly sensitive to photoperiod. Termination of diapause in D. similis did not require a cold or chilling period. All individuals from critical photoperiod trials were kept at 22°C to determine the duration of diapause. Diapausing individuals emerged from the cocoon after 82-105 days, compared to 6-23 days for individuals not entering diapause.