Instar- and Stage-Specific Photoperiodic Diapause Response of Lygus hesperus (Hemiptera: Miridae)

The western tarnished plant bug (Lygus hesperus Knight) (Hemiptera: Miridae) is a polyphagous pest of numerous western crops. This pest overwinters in a relatively short duration adult diapause, but many details regarding diapause induction and maintenance remain unstudied. Instar-specific responses to a switch from short (10-h) to long (14-h) days, long to short days, and a temporary (4-d) switch from short to long days were compared with responses of insects maintained under respective short- and long-day photoperiods. Influences of short days received during the nymphal stage on subsequent adult reproductive development under long days were also examined. Substantial diapause responses were observed only for insects switched to short days by 4th instar. Few insects that switched from short to long days exhibited diapause characters by Day 10 of adulthood. When 2nd instars were temporarily switched from short to long days no effect on the diapause response was observed, but the response was diminished when the switch occurred beginning at 4th instar. Reproductive development of adults reared under short days and switched to long days was modestly delayed compared with insects reared from egg to adult under long days. These results indicate the diapause response is elicited by short day cues received prior to the 5th instar, and that continued exposure to short days is necessary to maintain the adult diapause. These findings, combined with earlier reports of diapause termination in the field, suggest that southern populations of L. hesperus may express a more dynamic and complex overwintering strategy than was previously recognized.