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, 14 (6), e0217484
eCollection

Ultraviolet Inflorescence Cues Enhance Attractiveness of Inflorescence Odour to Culex Pipiens Mosquitoes

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Ultraviolet Inflorescence Cues Enhance Attractiveness of Inflorescence Odour to Culex Pipiens Mosquitoes

Daniel A H Peach et al. PLoS One.

Abstract

Inflorescence patterns of ultraviolet (UV) absorption and UV-reflection are attractive to many insect pollinators. To understand whether UV inflorescence cues affect the attraction of nectar-foraging mosquitoes, we worked with the common house mosquito, Culex pipiens and with two plant species exhibiting floral UV cues: the tansy, Tanacetum vulgare, and the common hawkweed Hieraciumm lachenalii. Electroretinograms revealed that Cx. pipiens eyes can sense UV wavelengths, with peak sensitivity at 335 nm. Behavioural bioassays divulged that UV inflorescence cues enhance the attractiveness of inflorescence odour. In the presence of natural floral odour, female Cx. pipiens were attracted to floral patterns of UV-absorption and UV-reflection but preferred uniformly UV-dark inflorescences. Moreover, Cx. pipiens females preferred UV-dark and black inflorescence models to UV-dark and yellow inflorescence models. With feathers and pelts of many avian and mammalian hosts also being UV-dark and dark-coloured, foraging Cx. pipiens females may respond to analogous visual cues when they seek nectar and vertebrate blood resources.

Conflict of interest statement

The authors would like to state that their industrial sponsor, Scotts Canada Ltd, had no role in the study design; collection, analysis, and interpretation of data; writing of the paper; or decision to submit for publication. The authors would also like to state that their relationship with Scotts Canada Ltd does not alter their adherence to PLOS ONE policies on data sharing and materials. The authors declare that they have no financial or non-financial competing interests.

Figures

Fig 1
Fig 1. Photographs of common hawkweed and common tansy in the human-visible light range and UV light range.
Inflorescences of common hawkweed, Hieracium lachenalii (a,b), and common tansy, Tanacetum vulgare (c,d), photographed with a custom-built camera capable of taking images in the human-visible light range (a,c) and UV light range (b,d). Hieracium lachenalii (b) displays a prominent UV “bullseye” with UV-absorbing petal bases and UV-reflective petal apices.
Fig 2
Fig 2. General design for behavioural bioassays.
(a) Photo (front view) of the behavioural bioassay design, showing paired Delta traps inside a mesh cage, and the position of a conventional and UV light source. (b) Schematic drawing (top/lateral view) of the behavioural bioassay design, showing three side walls covered in black cloth, paired Delta traps, and the two light sources. For each bioassay replicate, 50 virgin, 1- to 3-day-old females were released into the cage, and trap captures were recorded 24 h later.
Fig 3
Fig 3. Summary of the experimental design to test attraction of female Culex pipiens to inflorescences of Hieracium lachenalii and Tanacetum vulgare, or to inflorescence models.
Test stimuli are presented in schematic drawings, with left and right sections presenting the human-visible and UV light image, respectively; grey and black in the UV light image indicate UV reflection (UV-bright) and UV absorption (UV-dark), respectively; hatched lines indicate that the inflorescence was covered by cheese cloth; odour from natural inflorescences was present in all experiments (see methods for details).
Fig 4
Fig 4. Spectral sensitivity of Culex pipiens compound eyes.
Electroretinograms (ERGs) showing the mean spectral sensitivity of compound eyes of 3- to 4-day-old female Culex pipiens that were dark-adapted (black lines; n = 5), green-adapted (green lines; n = 5), or UV-adapted (purple lines, n = 5). The shaded area around each line represents the standard error of the spectral mean.
Fig 5
Fig 5. Effect of visual and olfactory inflorescence cues on trap captures of 1- to 3-day-old female Culex pipiens.
Inflorescences of Hieracium lachenalii (Exp. 1) and Tanacetum vulgare (Exp. 2), respectively, are shown in schematic drawings, with left and right sections presenting the human-visible and UV-light image, respectively; hatched lines indicate the inflorescence was covered by cheese cloth. Visual inflorescence cues did enhance the effect of inflorescence odour under UV light (Exps. 1, 2) but did not under UV-deficient illumination (Exps. 3, 4). Uniformly UV-dark H. lachenalii inflorescences (as a result of sunscreen treatment) were more attractive than inflorescences with the natural UV absorption and UV reflectance pattern (Exp. 5). Numbers in bars indicate total number of mosquitoes responding. The boxed number in the centre of bars shows the response ratio (total number of mosquitoes captured divided by the total number of mosquitoes released expressed as percentage). For each experiment, an asterisk indicates a significant preference for a test stimulus (binary logistic regression model; p < 0.05).
Fig 6
Fig 6. Effect of UV absorption, UV reflection and colour of inflorescence models in the presence of inflorescence odour (occluded inflorescence) on trap captures of 1- to 3-day-old female Culex pipiens.
Inflorescence models are shown in schematic drawings, with left and right sections presenting the human-visible and UV light image, respectively. Yellow UV-dark models were more attractive than yellow UV-bright models (Exp. 6), whereas black UV-dark models were more attractive than yellow UV-dark models (Exp. 7), indicating an interaction between UV-darkness and colour. Numbers in bars indicate the total number of mosquitoes responding. The boxed number in the centre of bars shows the response ratio (total number of mosquitoes captured divided by the total number of mosquitoes released expressed as percentage). For each experiment, an asterisk indicates a significant preference for a test stimulus (binary logistic regression model; p < 0.05).

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References

    1. Foster WA. Mosquito sugar feeding and reproductive energetics. Annu Rev Entomol. 1995;40: 443–474. 10.1146/annurev.en.40.010195.002303 - DOI - PubMed
    1. Müller H. Die Befruchtung der Blumen durch Insekten. Leipzig: Wilhelm Engelmann; 1873.
    1. Stoutamire W. Mosquito pollination of Habenaria obtusata. Michigan Bot. 1968;7: 203–212.
    1. Thien L. Mosquito pollination of Habenaria obtusata (Orchidaceae). Am J Bot. 1969;56: 232–237.
    1. Brantjes NBM, Leemans JAAM. Silene otites (Caryophyllaceae) pollinated by nocturnal lepidoptera and mosquitoes. Acta Bot Neerl. 1976;25: 281–295.

Publication types

Grant support

The research was supported by scholarships to DP (Natural Sciences and Engineering Research Council of Canada [NSERC; https://www.canada.ca/en/science-engineering-research.html] PGSD; SFU Provost’s Prize of Distinction [https://www.sfu.ca/dean-gradstudies/awards/entrance-scholarships/provost-awards/ppd.html]; John H Borden Scholarship [http://esc-sec.ca/student/student-awards/#toggle-id-5]), a scholarship to EK (NSERC – Undergraduate Student Research Award), and by an NSERC - Industrial Research Chair to GG, with Scotts Canada Ltd. as the industrial sponsor. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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