Timing of short-day exposure influences diapause response of western tarnished plant bug

Authors: Spurgeon, Dale

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/6/2016
Publication Date: 5/22/2017
Citation: Spurgeon, D.W. Timing of short-day exposure influences diapause response of western tarnished plant bug. National Cotton Council Beltwide Cotton Conference. p.p. 542-546. 2017.

Interpretive Summary: The western tarnished plant bug is thought to over winter in a period of reproductive quiescence (adult diapause) induced by short daylengths. However, the life stages responding to the photoperiodic cue are poorly defined. Bugs were reared under a short (10-h) day length until they were dissected to determine diapause status as 10-d-old adults. For comparison, bugs were similarly reared under the short day length but were transferred to a long (14-h) day length at either 1st or 3rd instar, or as new adults. Reciprocal treatments were also observed using bugs initially reared under the long day length, where they were either maintained, or switched to the short day length. Only a single bug reared under short days and switched as a nymph to long days exhibited the diapause characters of enlarged fat reserves and paused reproductive development. Also, only a small portion (<10%) of bugs switched from short to long days as young adults retained the diapause characters by 10 days of adult age. Incidence of diapause was highest (55%) for bugs receiving only the short-day photoperiodic cue, or for those switched from long to short days as 3rd instar or younger nymphs (40-53%). No diapause response was observed for bugs switched from long to short days as young adults. These results indicate the photoperiodic cue received by 3rd and earlier instars elicits a response, and the incidence of diapause appears increased slightly with increased duration of exposure to the short day length. Exposure to long days was efficient at reversing diapause induction irrespective of earlier exposure to short days.

Technical Abstract: The western tarnished plant bug, Lygus hesperus, enters adult diapause in response to short photoperiods. However, the instars or stages responsive to the photoperiodic cue are poorly defined. Lygus were reared under short days (10 h) until they were dissected to determine diapause status as 10-d-old adults. For comparison, bugs similarly reared under short days were transferred to long days (14 h) at either 1st or 3rd instar, or as newly eclosed adults. In reciprocal treatments, bugs initially reared under long days were either maintained under long days or were switched to short days. Only one bug reared under short days and switched as a nymph (3rd instar) to long days exhibited diapause characters. Only a small portion of bugs (<10% of both genders combined) switched from short to long days as young adults retained the diapause characters by 10 days of adult age. Incidence of diapause was highest (55%) for bugs receiving only the short-day photoperiodic cue, or for those switched from long to short days as 3rd or earlier instars (40-53%). Diapause was not observed among bugs switched from long to short days as young adults. These results indicate the photoperiodic cue elicits a response in at least 3rd and earlier instars, and suggest the incidence of diapause increases slightly with increased exposure to the short day length. Exposure to long days was efficient at reversing diapause induction irrespective of earlier exposure to short days.