Not to rain on anyones parade but there is a couple of problems with your experiment that I thought should be mentioned before anyone runs out and starts mass feeding insects to their fish, especially young growouts. For a starter, tilapia will show decent growth when fed sh. sandwiches, which is why they are used on commercial farms in 3rd world countries where the funds for commercial aquaculture feed is very limited. Not all fish will appreciate a groundnut cake.
Secondly, the insects that are easily found in North America do not typically consist of 90% protein. Even on a dry matter basis (moisture removed) the more commonly found insects that are fed in captivity average 40-70$ crude protein. As far as crude protein goes that's still impressive, but the main problem of most insects fed in captivity is that they are very poor sources of calcium. Over time this can result in an unbalanced calcium-phosphorus ratio, which can result in serious health issues.
For those interested please refer to Table 1, and Table 2, in the following document.
FEEDING CAPTIVE INSECTIVOROUS ANIMALS: NUTRITIONAL ASPECTS OF INSECTS AS FOOD
http://www.nagonline.net/Technical Papers/NAGFS00397Insects-JONIFEB24,2002MODIFIED.pdf
HTH
