Megachile willughbiella males chasing females.

Megachile chasing graph1

Megachile willughbiella males are patrolling patches of flowers. Females are flying from flower to flower gathering pollen. When a female sitting on a flower is detected the male is starting chasing behaviour. An example of this behaviour is visualized here. The male position and direction is given by a line with a dot. The dot is the position of the male face, the line is indicating the direction of the long axis of the body. The lines are drawn in 30 ms intervals. The female position is given by “o” for each 30 ms interval. In the picture given above the male, when detecting a female, at first is continuing its course and then is abruptly flying backwards away from the female before starting the chase of the female. The female is landing at a flower (Lathyrus  latifolius). In the figure, the unit of length is the length of the male.

To gain insight in the behaviour, the experimental results are compared with a phenomenological 2D model. The model consists basically of two parts, a control system controlling the distance to the female and a system for controlling the body axis in the direction of the female. The model needs 9 parameters : 3 timeconstants, 3 gains ( the gain for distance control and two gains for bodyrotation) the reference distance before and after the backward part of the path and a threshold to change over from high to low reference distance. The starting values are the values of vM (direction and size) and the startposition and body direction. The starting values are adapted from the experiment with fine tuning to obtain a better fit between model and experiment. Results of the model are given below. A striking feature of the experimental path is the backward movement of the male followed by a chase ending in contact with the female. The model is able to generate a reasonable fit with the experiment.

Megachile chasing model1

Parameters : Kr = 14, KrB=10, KdB=0, τv = 0.04 s,  τ = 0.15 s, τf = 0.04 s

The reference distance rref is chosen 6.1 at the start to change to 1 when |r|>6.1+1.3=7.4

(Track 090629_1548A)

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