Complex sentence: Plum curculio larvae are typically 6 to 9 mm long when fully grown, when they reach the pupal stage measuring about 5 to 7 mm; all adult characteristics are visible in this stage prior to transformation.
Split into simpler sentences: Plum curculio larvae are typically 6 to 9 mm long when fully grown. After this, the beetle reaches the pupal stage measuring about 5 to 7 mm; all adult characteristics are visible in this stage prior to transformation.