Parker Josephine E A, Angarita Jaimes Natalia C, Gleave Katherine, Mashauri Fabian, Abe Mayumi, Martine Jackline, Towers Catherine E, Towers David, McCall Philip J
Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
Optical Engineering Group, School of Engineering, University of Warwick, Coventry, CV4 7AL, UK.
Malar J. 2017 Jul 4;16(1):270. doi: 10.1186/s12936-017-1909-6.
Understanding how mosquitoes respond to long lasting insecticide treated nets (LLINs) is fundamental to sustaining the effectiveness of this essential control tool. We report on studies with a tracking system to investigate behaviour of wild anophelines at an LLIN, in an experimental hut at a rural site in Mwanza, Tanzania.
Groups of adult female mosquitoes (n = 10 per replicate) reared from larvae of a local population, identified as predominantly (95%) Anopheles arabiensis, were released in the hut. An infrared video tracking system recorded flight and net contact activity over 1 h as the mosquitoes attempted to reach a supine human volunteer within a bed net (either a deltamethrin-treated LLIN or an untreated control net). A range of activities, including flight path, position in relation to the bed net and duration of net contact, were quantified and compared between treatments.
The total time that female An. arabiensis spent in flight around LLINs was significantly lower than at untreated nets [F(1,10) = 9.26, p = 0.012], primarily due to a substantial reduction in the time mosquitoes spent in persistent 'bouncing' flight [F(1,10) = 18.48, p = 0.002]. Most activity occurred at the net roof but significantly less so with LLINs (56.8% of total) than untreated nets [85.0%; Χ (15) = 234.69, p < 0.001]. Activity levels at the bed net directly above the host torso were significantly higher with untreated nets (74.2%) than LLINs [38.4%; Χ (15) = 33.54, p = 0.004]. 'Visiting' and 'bouncing' rates were highest above the volunteer's chest in untreated nets (39.9 and 50.4%, respectively) and LLINs [29.9 and 42.4%; Χ (13) = 89.91, p < 0.001; Χ (9) = 45.73, p < 0.001]. Highest resting rates were above the torso in untreated nets [77%; Χ (9) = 63.12, p < 0.001], but in LLINs only 33.2% of resting occurred here [Χ (9) = 27.59, p = 0.001], with resting times spread between the short vertical side of the net adjacent to the volunteer's head (21.8%) and feet (16.2%). Duration of net contact by a single mosquito was estimated at 204-290 s on untreated nets and 46-82 s on LLINs. While latency to net contact was similar in both treatments, the reduction in activity over 60 min was significantly more rapid for LLINs [F(1,10) = 6.81, p = 0.026], reiterating an 'attract and kill' rather than a repellent mode of action.
The study has demonstrated the potential for detailed investigations of behaviour of wild mosquito populations under field conditions. The results validate the findings of earlier laboratory studies on mosquito activity at LLINs, and reinforce the key role of multiple brief contacts at the net roof as the critical LLIN mode of action.
了解蚊子如何对长效杀虫剂处理蚊帐（LLINs）做出反应，对于维持这一重要控制工具的有效性至关重要。我们报告了一项在坦桑尼亚姆万扎农村地区的实验小屋中，利用追踪系统对野生按蚊在LLINs处行为进行研究的情况。
将从当地种群幼虫饲养的成年雌性蚊子组（每个重复组n = 10只）释放到小屋中，这些蚊子经鉴定主要（95%）为阿拉伯按蚊。一个红外视频追踪系统记录了蚊子试图进入蚊帐内仰卧的人类志愿者（使用的是经溴氰菊酯处理的LLIN或未处理的对照蚊帐）时，1小时内的飞行和与蚊帐接触的活动。对包括飞行路径与蚊帐的相对位置以及与蚊帐接触的持续时间等一系列活动进行了量化，并在不同处理之间进行了比较。
阿拉伯按蚊雌性蚊子在LLINs周围飞行的总时间显著低于未处理蚊帐[F(1,10) = 9.26，p = 0.012]，这主要是由于蚊子在持续“弹跳”飞行中花费的时间大幅减少[F(1,10) = 18.48，p = 0.002]。大多数活动发生在蚊帐顶部，但LLINs的活动显著少于未处理蚊帐（占总数的56.8%）[85.0%；Χ(15) = 234.69，p < 0.001]。宿主躯干正上方蚊帐处的活动水平，未处理蚊帐（74.2%）显著高于LLINs [38.4%；Χ(15) = 33.54，p = 0.004]。在未处理蚊帐中，志愿者胸部上方的“探访”和“弹跳”率最高（分别为39.9%和50.4%），LLINs中则为[29.9%和42.4%；Χ(13) = 89.91，p < 0.001；Χ(9) = 45.73，p < 0.001]。未处理蚊帐中最高的停歇率在躯干上方[77%；Χ(9) = 63.12，p < 0.001]，但在LLINs中只有33.2%的停歇发生在此处[Χ(9) = 27.59，p = 0.001]，停歇时间分布在蚊帐靠近志愿者头部的短垂直边（21.8%）和脚部（16.2%）之间。单个蚊子与蚊帐接触的持续时间估计在未处理蚊帐上为204 - 290秒，在LLINs上为46 - 82秒。虽然两种处理中与蚊帐接触的潜伏期相似，但LLINs在60分钟内活动的减少明显更快[F(1,10) = 6.81，p = 0.026]，再次强调了“吸引并杀死”而非驱避的作用方式。
该研究证明了在野外条件下对野生蚊子种群行为进行详细调查的潜力。结果验证了早期关于蚊子在LLINs处活动的实验室研究结果，并强化了蚊帐顶部多次短暂接触作为LLINs关键作用方式的重要性。
