Non-destructive detection of diapause in males of the western tarnished plant bug

Authors: Spurgeon, Dale

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/3/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: Southern populations of the western tarnished plant bug survive the late-fall and early-winter in a state of dormancy called adult diapause. Because this diapause does not last until spring, it is not clear how it integrates with other survival tactics to ensure overwintering survival of the population. Development of potential cultural, biological, or molecular control tactics to impact this important cotton pest during the overwintering period would require a more complete picture of the ecological consequences of diapause. An obstacle to studying the survival impacts of diapause stems from the inability to identify diapausing individuals without dissecting them. Abdomen color appears a useful method for predicting diapause in females, but no comparable method is available for males. An ARS scientist at the Arid-Land Agricultural Research Center, Maricopa, AZ, found that the abdomen of a diapausing male plant bug becomes longer, compared with a reproductive male, in response to accumulation of fat. When this character (abdomen length) was compared with diapause assessments by dissection, it could distinguish diapause in the male bugs with about 91% accuracy. Once this method is validated, it should enable improved studies of plant bug overwintering survival, and of molecular-based tactics intended to reduce the survival value of diapause.

Technical Abstract: Southern populations of the western tarnished plant bug, Lygus hesperus Knight, survive the late-fall and early-winter in adult diapause. Because this diapause is short, it is not clear how it integrates with other survival tactics to ensure overwintering survival of the population. Reports of extended development times and survival of immature stages and reproductive adults under low temperatures, and presence of springtime diapausing adults in the field, add to the potential complexity of Lygus overwintering ecology. A comprehensive picture of L. hesperus overwintering requires knowledge of the implications of diapause, including advantages from extended host-free survival. An obstacle to interpreting host free survival is lack of a non-destructive method to distinguish diapause in individual insects. Abdomen color appears to have utility for predicting diapause for females, but no comparable method is available for males. Morphological measurements were examined for association with diapause, based on observed abdominal distention in males possessing a hypertrophied fat body. Rearing insects at 26.7 degrees C under short (10-h) days produced a mixture of reproductive and diapausing bugs. Measurements taken at 10 d of adult age were compared with diapause status determined by dissection. Corrected abdomen length (i.e., divided by head capsule width) was associated with reproductive and diapause status. Classification errors were minimized using a corrected abdomen length of 2.8, where accuracy was 90.6%. Once validated, this method should facilitate studies to unambiguously determine host-free survival of diapausing bugs, which will provide insights necessary to further examine the role of diapause in L. hesperus overwintering in southern climates.