3.5.2.5. Diameter of the spermatheca

The diameter of the spermatheca is evaluated with or without the tracheal net which surrounds it. The diameter is a direct estimation of the volume and an indirect estimation of the number of spermatozoa. Digital photographs and measurements with the use of an Image Analysis system give very accurate results. Without this system, measurements of the diameter can be performed using an eye-piece ocular micrometer.

1. Measure, two cross diameters because spermathecae do not always have a perfect spherical shape.

2. Calculate average value in mm.

Before the tracheal net is removed, the full spermatheca should have a diameter >1.2mm. One can use this measure for spermatheca volume to calculate the theoretical maximum storage capacity and percentage filled for spermatheca (see Tarpy et al., 2011).

3. Remove the tracheal net.

The spermatheca of a mated queen is white milky colour, while the one of an unfertilized queen is transparent (Fig. 47).