Diapause Termination, Gonoactivity, and Differentiation of Host-Seeking Behavior from Blood-Feeding Behavior in Hibernating Culex Tarsalis (Diptera: Culicidae)

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Abstract
Diapausing Culex tarsalis were collected from mine tunnels in Boulder Co., Colorado, during late September and early October 1980 and studied in the laboratory. Exposure to a long photophase (L:D 15:9) resulted in diapause termination in essentially all mosquitoes by day 7 at 25 °C. Warming alone (at 25 °C) for up to 8 days did not terminate diapause in a significant proportion of females maintained at typical autumn day lengths. Diapause was terminated in Cx. tarsalis by topical application of methoprene, a juvenile hormone (JH) mimic, suggesting that the physiological pathway for diapause termination involves secretion of JH by a reactivated corpus allatum. Host seeking and blood feeding were shown to represent discrete stages in the biting cycle of Cx. tarsalis , and these were differentiated in diapausing females by varying the size of the feeding chamber. Diapausing females could be induced to take a blood meal only when the host-seeking step in the biting cycle was bypassed by placing the females in close proximity to a host. Gonotrophic dissociation occurred in a significant proportion of females only when 3 conditions were met: females had to be in a state of diapause when fed, and fed females had to be incubated at a cool temperature (15 °C) and under short-day conditions during the time of blood meal digestion. The demonstration that gonotrophic dissociation can occur under experimental conditions probably has no relation to what occurs in nature. Warm Indian-summer conditions notwithstanding, typically short autumn day lengths are sufficient to suppress host-seeking behavior in diapausing populations and host seeking is a requisite for blood feeding in nature.