Fate of the blood meal in force-fed, diapausing Culex pipiens (Diptera: Culicidae).

Diapausing Culex pipiens L. do not display host-seeking behavior and can be induced to take blood only by being placed in contact with or in proximity to a host for prolonged periods. Such "force-fed" females do not use the blood for lipogenesis, and only some of them use the blood to initiate vitellogenesis. Diapausing Cx. pipiens that are induced to feed eject an average of 4.2-4.6 microliters of blood during overnight feeding periods compared with an average of 0.1 microliters for nondiapausing controls. The reduced avidity of diapausing females for blood, even under optimum conditions, and the ejection by fed females of blood volumes in excess of volumes usually retained indicate that such females are not physiologically programmed for taking and retaining blood. Data for uric acid and hematin excretion and bloodmeal volumes retained by diapausing females are positively correlated with diapause termination and yolk deposition. The occurrence of gonotrophic dissociation need not be invoked to explain the failure of some diapausing females to initiate vitellogenesis following a blood meal. Instead, this is explained by retention of small quantities of blood followed by incomplete digestion and is the expected result of a dose-dependent phenomenon determined by threshold blood volumes. Our data support the concept that the overwintering strategy of Cx. pipiens is limited to gonotrophic concordance in which overwintering females in nature do not take blood or develop eggs until diapause is terminated.