Research ArticleECOLOGY

Lidar reveals activity anomaly of malaria vectors during pan-African eclipse

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Science Advances  13 May 2020:
Vol. 6, no. 20, eaay5487
DOI: 10.1126/sciadv.aay5487
  • Fig. 1 Views from above.

    (A) The pan-African annular eclipse on 1 September 2016, as seen at 11:45 local time from the geostationary Meteosat-10 orbiting at an altitude of 35,786 km. The location of the lidar is indicated with an arrow. (B) A close-up aerial view of the agricultural patches and the periphery of Lupiro village with the lidar transect indicated by the red line.

  • Fig. 2 Three examples of mosquito observations during the eclipse.

    The figures display backscattered intensity as a function of time, range, and frequency. The frequency is color-coded, whereby the mosquito pitch appears red. The nonoscillatory backscatter from the body appears yellow. Atmospheric turbulence is seen as a blue surface in the bottom of the plots. The corresponding time signal is shown on the back of the figure with an arbitrary scale, but the peak cross section is in the legend. The frequency content is projected onto the left panes. The three cases are (A) 430-Hz presumed Anopheles female also displaying an overtone and (B) 590-Hz and (C) 650-Hz presumed males of either Anopheles (probably An. arabiensis) or Culex spp.

  • Fig. 3 Average modulation power spectra of the aerofauna during different times of the day.

    While the power spectra differ with the time of day, distributions for the same time intervals are consistent between consecutive days (same color graphs). During the eclipse on 1 September, the high-frequency content displays maximal power in the range associated with mosquitoes. In the evening, following the eclipse, reduced activity is displayed around 300 Hz before and after sunset. This is later compensated for during the night between 2 and 3 September. The absolute number of observations is stated in the legend in thousands per hour, and we note that the activity during the eclipse reaches a third of that of a normal evening rush hour. Approximate frequency ranges of Anopheles and Culex wingbeats are indicated underneath the power spectrum curves for both sexes. The gray arrows provide rough indications of possible frequency shifts from temperature and mosquito biomass payload. (For methodological and interpretational details, see the Supplementary Materials.) In addition, the lidar full width at half maximum (FWHM) resolution for a 23-ms time window is indicated.

  • Fig. 4 The observations were grouped in 20 clusters by HCA by considering the resemblance of the modulation spectra.

    The top part displays the dendrogram and relative cluster assignment fractions. The bottom part displays the 20 centroid spectra and within-group variances. The power scale is the same for all subfigures. The fundamental tones and the first three overtones are indicated. The overtones are subjected to the folding artifact, see, e.g., C5, and in some cases, e.g., C6, the fundamental and second harmonics are ambiguous. We have indicated our interpretation of the cluster in each subfigure. The interpretation is based on features in the centroid spectra neglecting details within the group variance. Other particular features in range and time were used to assign some of the low-frequency clusters. The ambiguous cases C6, C14, and C15 were not included in the subsequent analysis of mosquito activity patterns.

  • Fig. 5 Time-dependent probability of observation of various insect groups (probability of observing each group during one diurnal cycle is set to 100%, the absolute and relative abundances are given in the previous figure).

    Sunlight level measurements are indicated in gray in the background (the fluctuations are due to patchy clouds). (A) Normal days (average of 2 to 5 September 2016). (B) The day of the eclipse (1 September 2016). The intervals from Fig. 3 are indicated at the top of the figures. The insect grouping interpretations are based on selected classifications in Fig. 4 and denominated with identical labels. Uncertain groups are not included.

  • Table 1 Insect activity of the various groups during ordinary days compared to the day of the eclipse.

    Upper values are medians, and indicated spread is an interquartile range (IQR). The environmental conditions are given in the right columns. The selected hours have equivalent light levels to the eclipse.

    Embedded Image

    *Note that eclipse activity of the twilight insects is broader, see Fig. 5B.

    Supplementary Materials

    • Supplementary Materials

      Lidar reveals activity anomaly of malaria vectors during pan-African eclipse

      Mikkel Brydegaard, Samuel Jansson, Elin Malmqvist, Yeromin P. Mlacha, Alem Gebru, Fredros Okumu, Gerry F. Killeen, Carsten Kirkeby

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      The PDF file includes:

      • Supplementary Methods
      • Figs. S1 to S4
      • Table S1
      • Legend for data file S1

      Other Supplementary Material for this manuscript includes the following:

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