Non-Destructive Detection of Diapause in Males of the Western Tarnished Plant Bug

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.