Acoustic mating in malaria mosquitoes: From signalling logic to vector control

自从有记录以来，人类就一直在与蚊子传播的疾病作斗争。历史上的例子包括罗马人用来抗击热病爆发的大型沼泽排水系统，或者希腊剧作家/历史学家希罗多德(公元前484-425年)的著作。世卫组织报告了古埃及人为避免蚊子叮咬而采取的措施。今天，数百万人被迫睡在浸透杀虫剂的蚊帐下，以保护自己免受疟疾蚊子潜在致命叮咬的伤害。在人类住房内或附近观察到蚊子栖息的表面，通常会喷洒长效杀虫剂。最有效的控制措施是更好地了解蚊子病媒本身的生态和行为。但是，在疾病传播率较低的时候，药效可能会导致自满，或者由于目前在世界各地传播的抗药性蚊子种群的进化，药效可能会失效。此外，蚊子行为的变化，例如户外叮咬事件的增加，也威胁到当前的疾病控制措施。需要新的战略，特别是在持续的气候变化即将进一步加剧全球蚊子威胁的情况下。疾病只通过雌性蚊子传播，因为只有雌性蚊子需要血液才能繁殖。因此，雄性蚊子的研究仍然不足，它们作为新控制战略目标的潜力仍然没有得到充分开发。雄性交配群体是蚊子繁殖的关键组成部分。每到黄昏，雄性蚊子就聚集在一起吸引雌性交配伙伴。在疟疾蚊子按蚊中，这些蚊群可以由1000多只雄性蚊子组成。在蜂群中，雌性通过不同的飞行音调在声学上被识别。在大多数蚊子中，雄性蚊子比雌性蚊子产生更高的飞行音调(在28摄氏度下，雄性蚊子产生~800赫兹，雌性蚊子产生~550赫兹)。雌性(和雄性)产生的飞行音调也取决于外部温度，但尚不清楚雄性的偏好是否会随着温度的变化而发生类似的变化。此外，雄性似乎会调整自己的飞行音调，以回应雌性的声音，这表明这是一种双向交流，但各自的细节尚不清楚。雄性的飞行音调更复杂，它是在触角耳朵后面产生的。这意味着女性的飞行音调必须与男性的飞行音调竞争或合作，才能被听到。蚊子的进化似乎更倾向于合作的方式：在它们的耳朵里，两种音调相互作用，产生可预测的“扭曲产物”(DPS)。在特定的音调间隔，DPS实际上可以比原始音调更容易被听到。我们的项目建议对这种通讯系统的信号(飞行音调)和接收器(触角耳朵)进行系统的分析。我们将通过在严格控制的环境条件下对成群的雄性和雌性进行录音，来探索温度如何影响飞行音调频率。同时，我们将研究它们的触角耳朵在相同环境条件下的灵敏度。为此，我们将使用最先进的生物力学和电生理记录，并最终将在专门设计的行为实验中验证我们的发现。在迈向新型媒介控制工具的第一步中，该项目的结果将直接用于为雄性按蚊设计新型声学诱饵。在后续步骤中，我们将推广我们的发现，使其适用于其他蚊子媒介物种。声波诱饵可以用来减少人类居住地周围的蚊子数量(捕捉和杀死)，或者可以将它们纳入人口监测计划，为其他媒介控制计划提供信息。

Humans have been combatting mosquito-transmitted diseases for as long as records exist. Historic examples include the large marsh drainage schemes used by the Romans to combat fever outbreaks or the writings of the Greek playwright/historian Herodotus (484-425 B.C.) who reports on the measures ancient Egyptians took to avoid mosquito bites. Today, millions of people are forced to sleep under insecticide impregnated bed nets to shield themselves from the potentially deadly bite of the malaria mosquito Anopheles. Surfaces within or nearby human housing, upon which mosquitoes have been observed to rest are routinely sprayed with long-lasting insecticides. The most effective control measures have emerged from a better understanding of the ecology and behaviour of the mosquito disease vectors themselves. But efficacy can lead to complacency in times of low disease transmission or it can simply expire due to the evolution of insecticide resistant mosquito populations, currently spreading throughout the world. Also changes in mosquito behavior, e.g. increasing occurrences of outdoor biting, threaten current disease control measures. Novel strategies are required, especially as the ongoing climate change is about to further exacerbate the global mosquito threat. Disease is transmitted by female mosquitoes only, as only females require a blood-meal for reproduction. As a result, male mosquitoes have remained under-researched and their potential as targets for novel control strategies has remained underexploited. Male mating swarms are a key component of mosquito reproduction. Each dusk, male mosquitoes aggregate to attract female mating partners. In the malaria mosquito Anopheles, these swarms can be formed by 1,000s of males. Within the swarm, females are identified acoustically by their different flight tones. In most mosquitoes, males produce a higher flight tone than females (~800Hz males vs ~550Hz female at 28 degrees Celsius for Anopheles coluzzii). Flight tones produced by females (and males) also depend on the external temperature but it is unknown if the males' preferences similarly change with temperature. Also, males appear to modulate their own flight tones in response to a female tone suggesting that this is a two-way communication, yet the respective details are unclear.Further complexity is added by the male's own flight tone, which is produced closely behind his antennal ears. This means the female flight tone must either compete against, or cooperate with, the male's flight tone in order to be heard. It seems that mosquito evolution has favoured the cooperative approach: Within their ears, the two tones interact and produce predictable 'distortion products' (DPs). At specific tone intervals, DPs can actually be more audible than the original tones. Our project proposes a systematic analysis of the signals (flight tones) and the receivers (antennal ears) of this communication system in the malaria mosquito Anopheles coluzzii. We will explore how temperature affects flight tone frequency by performing audio recordings of swarming males and females under strictly controlled environmental conditions. At the same time we will study the sensitivity of their antennal ears under the same environmental conditions. To this end, we will use state-of-the art biomechanical and electrophysiological recordings and we will finally verify our findings in specifically designed behavioural experiments. In a first step towards novel vector control tools, the results from this project will be used to directly inform the design of novel acoustic lures for male Anopheline mosquitoes. In a follow-up step, we will then generalize our findings to make them applicable to other mosquito vector species. Acoustic lures can be used to reduce mosquito populations (catch and kill) around human habitation or they can be incorporated into population surveillance programs to inform other vector control programs.