Diapause in tarnished plant bug (Heteroptera: Miridae) reared in dynamic photoperiod environmental cabinets

Diapause in tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois) (Heteroptera: Miridae), increased with decreasing photoperiods simulated in environmental cabinets to match those at Starkville, Mississippi (latitude 33.45 N). Hypertrophied fat body in males was strongly associated with hypotrophied accessory glands, and these two characteristics were used to classify male diapause. Although the fatty tissue surrounding the testes differentiated diapausing and reproductive males, almost all males had well-developed testes and large quantities of sperm in their seminal vesicles at the time of dissection; thus testis size was not used for diapause classification. Hypertrophied fat body and lack of mature eggs at time of dissection were used to classify female diapause. Simulated decreasing photoperiods beginning on 4 September, 17 September, and 1 October (Julian dates 247, 260, and 274, respectively) resulted in 15.4%, 57.0%, and 86.0% diapause, respectively. Males and females exhibited similar percentages of diapause. When only egg-producing females were considered, fewer eggs were present at time of dissection within females with the largest fat bodies than within females with smaller fat bodies. Diapause morphology was rated numerically and an SAS program was developed to classify diapausing and reproductive insects. Extrapolation from current data indicated that 50% of nymphs eclosing from eggs oviposited near Starkville, Mississippi, about 14 September can be expected to enter diapause.