Instar- and stage-specific photoperiodic diapause response of Lygus hesperus (Hemiptera: Miridae)

Authors: Spurgeon, Dale

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2017
Publication Date: 12/23/2017
Citation: Spurgeon, D.W. 2017. Instar- and stage-specific photoperiodic diapause response of Lygus hesperus (Hemiptera: Miridae). Journal of Insect Science. 17(6):125.

Interpretive Summary: The western tarnished plant bug is an important pest of numerous western crops including cotton. This pest is widely considered to overwinter as an adult in a relatively short dormancy called diapause. The diapause is characterized by an increase in body fat and lack of development of reproductive organs, but the details of how diapause is induced or maintained are poorly known. Better understanding of plant bug overwintering would be useful to assess the potential for management of populations during the non-cropping season. An ARS scientist at Maricopa, AZ demonstrated that the adult dormancy was induced by exposure of the first four stages of the nymph to short (10 hour) daylengths. Exposure of the fifth (and final) nymphal stage, or of adults, to the short days produced few diapausing adults. Exposure of nymphs or adults to long (14 hour) days negated the diapause-inducing effects of the short days, although a temporary exposure to long days did not prevent diapause so long as exposure to short days was resumed. When adult bugs newly induced into diapause were exposed to long days, they resumed development of the reproductive organs after a short delay of only a few days. These results showed that continued exposure to short days is necessary to maintain the diapause. These findings, combined with earlier reports that diapause typically ends in late fall or early winter, suggest that southern populations of this plant bug may have multiple or overlapping populations during the winter. Therefore, this pest may express a more dynamic and complex overwintering strategy than was previously recognized.

Technical Abstract: 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 switched from short to long days exhibited diapause characters as 10-d-old adults. 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.