Laboratory of Entomology, Wageningen University & Research, P.O. Box 16, 6700 AA, Wageningen, The Netherlands.
SACIDS Foundation for One Health, Sokoine University of Agriculture, Chuo Kikuu, P.O. Box 3297, Morogoro, Tanzania.
Malar J. 2021 Jan 21;20(1):52. doi: 10.1186/s12936-020-03575-0.
Olfactory cues have been shown to have an important role in guiding gravid mosquito females to selected sites for egg laying. The objective of this study was to determine the influence of emanations from soil from a breeding site and the putative oviposition pheromone nonane on oviposition-site selection of natural populations of Anopheles gambiae sensu lato (s.l.) and Culex quinquefasciatus.
This field-based study was conducted in Mvomero District in East-central Tanzania. In a dual-choice experimental set up, clay bowls were dug into the ground and filled with one of the following treatments: (i) distilled water + autoclaved soil (control), (ii) distilled water + soil from a natural mosquito breeding site, (iii) distilled water + nonane and (iv) distilled water + nonane + soil from a natural breeding site. Soil was dried and autoclaved or dried only before use. After five days of incubation, larvae were collected daily for 10 days. The median number of larvae per bowl per day was used as outcome measure.
Autoclaved soil had a significant attractive effect on oviposition behaviour of Cx. quinquefasciatus (median values ± s.e: 8.0 ± 1.1; P < 0.005) but no effect on An. gambiae (median value ± s.e: 0.0 ± 0.2; P = 0.18). Nonane and emanations from untreated soil significantly and positively influenced the selection of oviposition sites by both An. gambiae s.l. (median values ± s.e.: 12.0 ± 2.0 and 4.5 ± 1.5, respectively; P < 0.0001) and Cx. quinquefasciatus (median values ± s.e.: 19.0 ± 1.3 and 17.0 ± 2.0, respectively; P < 0.0001). A mixture of nonane and untreated soil caused a synergistic effect on oviposition behaviour in An. gambiae s.l. (median value ± s.e.: 23.5 ± 2.5; P < 0.0001) compared to either nonane (median values ± s.e.: 12.0 ± 2.0; P < 0.0001) or untreated soil alone (median value ± s.e.: 4.5 ± 1.5; P < 0.0001). A synergistic effect of nonane mixed with untreated soil was also found in Cx. quinquefasciatus (median value ± s.e.: 41.0 ± 2.1; P < 0.0001) compared to either nonane (median value ± s.e. 19.0 ± 1.3; P < 0.0001) or untreated soil alone (median value ± s.e.: 17.0 ± 2.0; P < 0.0001). The oviposition activity index for An. gambiae was 0.56 (P < 0.001) and for Cx. quinquefasciatus 0.59 (P < 0.0001).
The larval pheromone nonane and emanations from breeding-site soil both induced oviposition in wild An. gambiae s.l. and Cx. quinquefasciatus, with a synergistic effect when both stimuli were present simultaneously. This is the first study in which nonane is shown to cause oviposition under natural conditions, suggesting that this compound can potentially be exploited for the management of mosquito vectors.
嗅觉线索已被证明在引导怀孕的雌蚊选择产卵地点方面发挥了重要作用。本研究的目的是确定土壤散发物和假定的产卵信息素壬烷对天然疟蚊属（s.l.）和库蚊属（Culex quinquefasciatus）种群的产卵地点选择的影响。
本研究在坦桑尼亚中东部姆沃罗罗区进行。在双选择实验设置中，将粘土碗挖入地下并填入以下处理之一：（i）蒸馏水+高压灭菌土（对照），（ii）蒸馏水+天然蚊子滋生地土壤，（iii）蒸馏水+壬烷和（iv）蒸馏水+壬烷+天然滋生地土壤。土壤先干燥后高压灭菌，或仅干燥后使用。孵育五天后，每天收集幼虫 10 天。每天每碗幼虫的中位数数量用作结果测量。
高压灭菌土对库蚊（Culex quinquefasciatus）的产卵行为有显著的吸引力（中位数±标准误差：8.0±1.1；P<0.005），但对疟蚊属（An. gambiae）没有影响（中位数±标准误差：0.0±0.2；P=0.18）。壬烷和未处理土壤的散发物显著且积极地影响了野生疟蚊属（s.l.）和库蚊属（Culex quinquefasciatus）的产卵地点选择（中位数±标准误差：分别为 12.0±2.0 和 4.5±1.5；P<0.0001）。壬烷和未处理土壤的混合物对疟蚊属（s.l.）的产卵行为产生协同作用（中位数±标准误差：23.5±2.5；P<0.0001），与壬烷（中位数±标准误差：12.0±2.0；P<0.0001）或未处理土壤单独使用（中位数±标准误差：4.5±1.5；P<0.0001）相比。壬烷与未处理土壤的混合物在库蚊（Culex quinquefasciatus）中也产生协同作用（中位数±标准误差：41.0±2.1；P<0.0001），与壬烷（中位数±标准误差：19.0±1.3；P<0.0001）或未处理土壤单独使用（中位数±标准误差：17.0±2.0；P<0.0001）相比。疟蚊属的产卵活动指数为 0.56（P<0.001），库蚊属为 0.59（P<0.0001）。
幼虫信息素壬烷和滋生地土壤散发物都诱导野生疟蚊属（s.l.）和库蚊属（Culex quinquefasciatus）产卵，当两种刺激同时存在时，具有协同作用。这是首次证明壬烷在自然条件下引起产卵的研究，表明该化合物可能可用于蚊子传播媒介的管理。
