Abstract
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 (Hartig), established from a feral Kentucky population. We investigated induction of diapause in the laboratory under photoperiods of 10:14, 11:13, 12:12, 13:11, 14:10, 15:9, and 16:8 (L:D) in the first trial, and added a photoperiod of 9:15 (L:D) in the second trial. Individuals exposed to light periods ≤12:12 (L:D) entered diapause; individuals in a photoperiod > 13:11 (L:D) bypassed diapause. The sensitive stage was determined using reciprocal switches of diapause-inducing (9:15) and non-diapause inducing (16:8) L:D regimes. Our 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 to 105 d, compared to 6 to 23 d for individuals not entering diapause.
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