Center for Vectorborne Diseases and Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
J Med Entomol. 2013 Jul;50(4):773-90. doi: 10.1603/me12280.
At temperate latitudes, Culex (Diptera: Culicidae) mosquitoes typically overwinter as adult females in reproductive arrest and also may serve as reservoir hosts for arboviruses when cold temperatures arrest viral replication. To evaluate their role in the persistence of West Nile virus (WNV) in the Sacramento Valley of California, the induction and termination of diapause were investigated for members of the Culex pipiens (L.) complex, Culex tarsalis Coquillett, and Culex stigmatosoma Dyar under field, seminatural, and experimental conditions. All Culex spp. remained vagile throughout winter, enabling the collection of 3,174 females and 1,706 males from diverse habitats during the winters of 2010-2012. Overwintering strategies included both quiescence and diapause. In addition, Cx. pipiens form molestus Forskäl females remained reproductively active in both underground and aboveground habitats. Some blood-fed, gravid, and parous Cx. tarsalis and Cx. pipiens complex females were collected throughout the winter period. Under both field and experimental conditions, Cx. tarsalis and Cx. stigmatosoma females exposed to autumnal conditions arrested primary follicular maturation at previtellogenic stage I, with primary to secondary follicular ratios <1.5 (indicative of a hormonally induced diapause). In contrast, most Cx. pipiens complex females did not enter reproductive diapause and ovarian follicles matured to >or=stage I-II (host-seeking arrest) or were found in various stages of degeneration. Diapause was initiated in the majority of Cx. tarsalis and Cx. stigmatosoma females by mid-late October and was terminated after the winter solstice, but host-seeking seemed limited by temperature. An accrual of 97.52 +/- 30.7 and 162.85 +/- 79.3 degree-days after the winter solstice was estimated to be necessary for diapause termination in Cx. tarsalis under field and seminatural conditions, respectively. An increase in the proportion of blood-fed Culex females in resting collections occurred concurrently with diapause termination in field populations based on ovarian morphometrics. WNV RNA was detected in one pool of 18 males and in a single blood-fed female Cx. tarsalis collected during winter. Therefore, both vertically and horizontally infected Culex females may persist through winter and possibly transmit WNV after diapause termination in late winter or early spring in the Sacramento Valley of California.
在温带地区，库蚊（双翅目：库蚊科）蚊子通常以处于繁殖静止期的成年雌性状态越冬，并且当低温抑制病毒复制时，它们也可能成为虫媒病毒的储存宿主。为了评估它们在加利福尼亚萨克拉门托谷西尼罗河病毒 (WNV) 持续存在中的作用，在野外、半自然和实验条件下，研究了库蚊属（L.）复合体、库蚊属（Coquillett）和库蚊属（Dyar）的滞育诱导和终止。所有的库蚊属物种在整个冬季都保持活跃，使我们能够在 2010 年至 2012 年的冬季从各种栖息地收集 3174 只雌性和 1706 只雄性。越冬策略包括静止和滞育。此外，库蚊属（Forskál）的库蚊属（molestus）Forskál 雌性在地下和地上栖息地均保持繁殖活跃。在整个冬季期间，一些吸食血液、怀孕和产仔的库蚊属（tarsalis）和库蚊属（complex）雌性被采集。在野外和实验条件下，暴露于秋季条件下的库蚊属（tarsalis）和库蚊属（stigmatosoma）雌性在卵黄前阶段 I 时停止初级卵泡成熟，初级到次级卵泡比 <1.5（表明激素诱导的滞育）。相比之下，大多数库蚊属（complex）雌性没有进入繁殖滞育，卵巢卵泡成熟至 >或=I-II 期（寻找宿主的停滞）或处于各种退化阶段。库蚊属（tarsalis）和库蚊属（stigmatosoma）雌性的滞育大多在 10 月中旬至下旬开始，并在冬至后结束，但寻找宿主似乎受到温度的限制。估计冬至后需要积累 97.52 +/- 30.7 和 162.85 +/- 79.3 度日才能分别在野外和半自然条件下终止库蚊属（tarsalis）的滞育。根据卵巢形态计量学，在野外种群中，与滞育终止同时，静息采集的吸血库蚊属雌性的比例增加。在冬季采集的 18 只雄性和一只吸血的库蚊属（tarsalis）雌性中检测到了 WNV RNA。因此，垂直和水平感染的库蚊属雌性可能会在冬季存活下来，并可能在加利福尼亚州萨克拉门托谷的冬季后期或早春结束时传播 WNV。
