Complex sentence: Wilt disease caused by a particular nucleopolyhedrovirus (LdNPV) that is specific to the gypsy moth is its most devastating natural disease, causeing a dramatic collapse of outbreak populations by killing both the larvae and pupae.
Split into simpler sentences: Wilt disease caused by a particular nucleopolyhedrovirus (LdNPV) that is specific to the gypsy moth is the most devastating of its natural diseases. NPV causes a dramatic collapse of outbreak populations by killing both the larvae and pupae.