Diapause response to photoperiod in an Arizona population of Lygus hesperus (Hemiptera: Miridae)

Authors: Spurgeon, Dale; Brent, Colin

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2015
Publication Date: 9/8/2015
Publication URL: http://handle.nal.usda.gov/10113/61420
Citation: Spurgeon, D.W., Brent, C.S. 2015. Diapause response to photoperiod in an Arizona population of Lygus hesperus (Hemiptera: Miridae). Journal of Entomological Science. 50:238-247.

Interpretive Summary: The western tarnished plant bug (Lygus bug) is a major pest of crops in the western U.S. This pest survives the winter as an adult in a state of diapause characterized by large fat reserves and undeveloped reproductive organs. The diapause state in this bug may represent an ecological vulnerability that is amenable to cultural management if it is sufficiently understood, but much about diapause in this pest remains unknown. When Lygus were reared from eggs to adults under daylengths ranging from 10 to 13 hours, the incidence of diapause increased with decreased daylength from 13 to 11 hours. The incidence of diapause at daylengths of 10 and 11 hours was similar. The maximum incidence of diapause was greater for female bugs (80%) than for male bugs (51%). These maxima were lower than those previously reported for Lygus bugs in California. In addition, the diapause response was widely variable at but the longest daylength (13 hours) where the incidence of diapause was low. The critical daylengths that induced diapause at a rate that was half the estimated maximum were 11 hours 54 min for females and 12 hours 7 min for males. The low but variable incidence of diapause that we observed was probably caused by variation in the natural population of Lygus in central Arizona. This variability may be important in allowing this population of Lygus bugs to adapt to local conditions where climate and host availability often permit reproduction on fall and winter alfalfa and weed hosts. Such geographical variation in diapause response is known for some other insects. Our results provide baseline information for comparison in future studies of the influences of geographical location and environmental factors on the diapause response of Lygus bugs.

Technical Abstract: The western tarnished plant bug (Lygus hesperus Knight) is an important crop pest in the western U.S. that overwinters in an adult diapause. However, knowledge of L. hesperus diapause is incomplete. Eggs from field-collected adults were reared under photoperiods of 10:14, 11:13, 12:12, and 13:10 (L:D) h at 26.7 +/- 1 degree C and the diapause response for each gender was modeled by a logistic function. Incidence of a novel fat body type was also examined by logistic regression. Validation studies using the same methods were subsequently conducted using photoperiods of 10.5:13.5, 11.5:12.5, and 12.5:11.5 (L:D) h. No effects of bug gender, photoperiod, or diapause status on occurrence of the novel fat type were detected. Estimates of diapause in validation studies were within confidence intervals for initial predictions, but systematic deviations from initial predictions prompted re-fitting of the models to include validation data. Re-fitted functions estimated critical photoperiods 11 h 44 min for females, and 11 h 21 min for males. The maximum incidence of diapause was lower for males than for females and was <100% for both genders. Re-fitted functions also predicted 50% of the population-specific maximum diapause response corresponded to photoperiods of 11 h 54 min (females) and 12 h 7 min (males). These results, combined with other recent findings, suggest heterogeneity in diapause response likely enables L. hesperus populations to adapt to local conditions. The estimated functions relating photoperiod to diapause incidence provide baselines to facilitate future studies of environmental and geographical influences on diapause in this species.