Parity and Longevity of <i>Aedes aegypti</i> According to Temperatures in Controlled Conditions and Consequences on Dengue Transmission Risks

Background In Guadeloupe, Aedes aegypti mosquitoes are the only vectors of dengue and chikungunya viruses. For both diseases, vector control is the only tool for preventing epidemics since no vaccine or specific treatment is available. However, to efficiently implement control of mosquitoes vectors, a reliable estimation of the transmission risks is necessary. To become infective an Ae. aegypti female must ingest the virus during a blood meal and will not be able to transmit the virus during another blood-meal until the extrinsic incubation period is completed. Consequently the aged females will carry more infectious risks. The objectives of the present study were to estimate under controlled conditions the expectation of infective life for females and thus the transmission risks in relation with their reproductive cycle and parity status. Methodology/Principal Findings Larvae of Ae. aegypti were collected in central Guadeloupe and breed under laboratory conditions until adult emergence. The experiments were performed at constant temperatures (± 1.5°C) of 24°C, 27°C and 30°C on adults females from first generation (F1). Females were kept and fed individually and records of blood-feeding, egg-laying and survival were done daily. Some females were dissected at different physiological stages to observe the ovaries development. The data were analyzed to follow the evolution of parity rates, the number of gonotrophic cycles, the fecundity and to study the mean expectation of life and the mean expectation of infective life for Ae. aegypti females according to temperatures. The expectation of life varies with the parity rates and according to the temperatures, with durations from about 10 days at low parity rates at the higher temperature to an optimal duration of about 35 days when 70% of females are parous at 27°C. Infective life expectancy was found highly variable in the lower parous rates and again the optimal durations were found when more than 50% of females are parous for the mean temperatures of 27°C and 30°C. Conclusion Parity rates can be determined for field collected females and could be a good proxy of the expectation of infective life according to temperatures. However, for the same parity rates, the estimation of infective life expectation is very different between Ae. aegypti and Anopheles gambiae mosquitoes. Correlation of field parity rates with transmission risks requires absolutely to be based on Ae. aegypti models, since available Anopheles sp. models underestimate greatly the females longevity.【背景】 在瓜德罗普地区，埃及伊蚊（Aedes aegypti）是登革热与基孔肯雅热病毒的唯一传播媒介。目前针对这两种疾病均无可用疫苗或特效治疗手段，因此媒介防控是预防疫情暴发的唯一工具。然而，要高效开展蚊媒防控工作，必须对传播风险进行可靠估算。雌性埃及伊蚊需在吸血过程中摄入病毒，且需完成外潜伏期（extrinsic incubation period）后，才能在后续吸血行为中传播病毒。由此可见，高龄雌蚊携带的感染风险更高。本研究旨在受控条件下，估算雌蚊的感染性寿命期望，进而探究其传播风险与生殖周期及产卵状态（parity status）的关联。 【方法/主要结果】 研究人员在瓜德罗普中部采集埃及伊蚊幼虫，于实验室条件下饲养至成虫羽化。实验分别在恒定温度（误差±1.5℃）24℃、27℃与30℃下，以第一代（F1）雌蚊为研究对象开展。雌蚊采用单只饲养方式并饲喂血液，每日记录其吸血、产卵及存活情况。部分雌蚊在不同生理阶段被解剖，以观察卵巢发育状况。通过数据分析，我们追踪了产卵率的动态变化、生殖营养周期次数、产卵量，并探究了不同温度下埃及伊蚊雌蚊的平均寿命期望与平均感染性寿命期望。 研究发现，雌蚊的寿命期望随产卵率与温度变化而改变：在高温条件下低产卵率个体的寿命时长约为10天；而在27℃时，当70%的雌蚊为已产卵个体时，寿命可达最优的约35天。感染性寿命期望在低产卵率组中呈现高度变异；同样，在27℃与30℃的平均温度下，当超过50%的雌蚊为已产卵个体时，感染性寿命期望达到最优时长。 【结论】 可通过野外采集的雌蚊确定其产卵率，该指标可作为不同温度下感染性寿命期望的良好替代指标。然而，在相同产卵率条件下，埃及伊蚊与冈比亚按蚊（Anopheles gambiae）的感染性寿命期望估算结果存在显著差异。将野外产卵率与传播风险进行关联分析时，必须基于埃及伊蚊的专属模型，因为现有按蚊属（Anopheles sp.）模型会极大低估雌蚊的寿命。