Complex sentence: The native silk spinning caterpillars were proving to be susceptible to disease so Trouvelot brought over gypsy moth eggs to try to make a caterpillar hybrid, that could resist diseases.
Split into simpler sentences: The native silk spinning caterpillars were proving to be susceptible to disease. So Trouvelot brought over gypsy moth eggs to try to make a caterpillar hybrid, that could resist diseases.