What is the body density of insects on average?
A recent studya measured the volumes (using a 3D scanner) and masses of 113 different insect species. They found the following relationship between the mass of the insects and their volumes ($V[mm^3]$ and $m[mg]$):

$\ln (V) = 1.019 \ln (m) + 1.46$

$\Leftrightarrow V = 4.30596 m^{1.019}$

Thus, since $\rho = \frac m V$

$\rho(m) = \frac m {4.30596 m^{1.019}} = \frac {0.232236} {m^{0.019}}
 $

Figure: Scatter plot of the measured masses and volumes



Reference:

a Kühsel, S., Brückner, A., Schmelzle, S., Heethoff, M. and Blüthgen, N. (2016), Surface area–volume ratios in insects. Insect Science. doi:10.1111/1744-7917.12362