HOW TO MEASURE DENSITY OF INSECTS

Why do we want to know the density? There are generally two reasons: 1). to find a suitable substitute material that has radiation scattering and attenuation properties similar to those of insects; 2). to simulate the system mathematically using computer codes, certain properties (such as density) should be known.

For this purpose, it is not really the density of an insect that is of interest. What is needed is the “bulk density”. In the case of insects (or corn flakes, rice, etc), there is air within the volume occupied by them. And thus the bulk density also includes the effect of this air. If the substance were a solid material like a piece of metal, the bulk density is the same as its density.

The method of measuring bulk density is as follows:

Measure out a known volume of insects – 100 mL is a good number. The best way is to use a graduated cylinder for the purpose. It is better to have a long cylinder rather than a flat one - the volume measurement is more accurate. The next step is to weigh this amount of insects on an analytical balance.

Bulk density is then the ratio between the mass (in gram) and the volume (in mL). Thus, the bulk density would be in the unit of g/mL.

Bulk density (g/mL) = mass (g) / volume (mL).


However, for both the purposes mentioned above, for two materials to have similar behavior under radiation, not only the density (rather, bulk density in our case) should be similar but also chemical composition. Elemental composition of tsetse pupae was recently measured at the Chemistry Department of University of Vienna and is reported by Mehta and Parker (2011).

K. Mehta and A. Parker, Characterization and dosimetry of a practical X-ray alternative to self-shielded gamma irradiators, Radiation Physics and Chemistry, 80, pp 107-113, 2011