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Title: Morphological characters of diapause in Lygus hesperus Knight (Hemiptera: Miridae)

item Spurgeon, Dale
item Brent, Colin

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2009
Publication Date: 10/26/2010
Citation: Spurgeon, D.W., Brent, C.S. 2010. Morphological characters of diapause in Lygus hesperus Knight (Hemiptera: Miridae). J. Entomol. Sci. 45(4):303-316.

Interpretive Summary: Development of management methods that reduce amounts of pesticides used to control the western tarnished plant bug in cotton will require better knowledge of how this pest interacts with its environment. In particular, the mechanisms by which plant bugs survive the winter are poorly known. Western tarnished plant bugs overwinter as adults in diapause, which is a state of reduced reproductive development and lowered metabolic rate caused by exposure to short daylengths. Previous reports of the relationship between daylength and entry into diapause are inconsistent, perhaps because different investigators used different characters to distinguish diapause. We evaluated characters of the body fat and reproductive organs to establish standardized methods for distinguishing diapause. The conditions of the male testes and sperm storage organs, and the color of fat deposits, were not reliable indicators of diapause. The most appropriate indicators of diapause appeared to be the presence of well developed fat deposits combined with 1) the absence of development of the specialized glands associated with the male reproductive system, or 2) the absence of ovary development in the female. Our descriptions and illustrations of these characters should permit more consistent identification of diapause in the western tarnished plant bug, and thereby facilitate meaningful comparisons of studies conducted by different investigators.

Technical Abstract: Development of management tactics that reduce reliance on conventional pesticides for control of the western tarnished plant bug, Lygus hesperus Knight, will require improved understanding of Lygus ecology. One poorly characterized aspect of Lygus ecology is the induction of adult diapause. Although photoperiod is a key regulator of diapause, previous research has reported inconsistent results, likely because of the different criteria used to distinguish diapause. To establish standardized criteria, we reared L. hesperus under photoperiods of 10- and 14-h and a constant temperature of 26.6°C. Adults were dissected at ages of 3, 7, 10, 14, and 17 days to evaluate associations among characteristics of the fat body and reproductive organs. Whereas most characters examined were at least weakly associated with others, we concluded that seminal vesicle condition, presence of a fatty sheath on the testis, and fat body color were not reliable indicators of L. hesperus physiological status. The most appropriate criteria for distinguishing diapause appeared to be hypertrophied fat bodies combined with undeveloped medial accessory glands (for males) or undeveloped ovaries (for females) in adults that were at least 10 days old. We also evaluated less stringent criteria, permitting some development of accessory glands or ovaries to accommodate the delayed reproductive development observed in some specimens reared under the 10-h photoperiod. The descriptions and illustrations of the morphological characters, combined with our suggested sets of criteria, should permit a more standardized assessment of L. hesperus physiological status, and thereby facilitate meaningful comparisons of research by different investigators.