Anthrax oscillation

 

Anthrax_oscil_anim

In this animation (6X retarded)  a female Anthrax anthrax is hovering near the nest entrance of a mason bee. Anthrax anthrax delivers mostly only one egg at each hole. Anthrax females will inspect the hole before shooting an egg (More information about the egg shot). After inspecting the hole Anthrax is starting a hovering phase before the hole, oscillating around an approximately constant distance. The oscillation is sometimes very pronounced as given in Fig. 1. In Fig 1 along the vertical axis  the distance between the head of the fly and a point at the rim of the hole is displayed as seen by the camera. The unit of distance here is the length of the fly. The fly is moving obliquely to the viewing axis of the camera approximately along a straight line. Therefore the distance as seen by the camera is approximately proportional to the real distance between the head of the fly and the point at the rim of the hole.

Anthrax_oscil_graph_250511_1528

Figure 1

Features :

From Fig.1 the characteristic features of the signal are :

  1. The female Anthrax is not diminishing the mean distance to the hole in anticipation of an egg shot.
  2. The distance is oscillating with a period of  0.21 s.
  3. The time between end of inspection and egg shot is 2.40 s.

The features  have been evaluated for more tracks, with the result :

  1. The female Anthrax is not diminishing the mean distance to the hole in anticipation of an egg shot.
  2. Oscillation is sometimes irregular. When regular for an interval > 0.6 s as in Fig. 6, the period is 0.195 ± 0.033 s (from 8  tracks)
  3. The time between end of inspection and egg shot is 1.89 ± 0.40 s. (from 11 Tracks)

 

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