Final answer:
Dutch elm disease is caused by the Ophiostoma ulmi fungus and spread by the elm bark beetle. The disease disrupts the tree's vascular system, leading to its eventual death. So, the correct answer is option b.
Step-by-step explanation:
Dutch elm disease is a destructive fungal infection caused by the fungus Ophiostoma ulmi. This disease affects various species of elm trees by invading their vascular system, ultimately disrupting water transport and causing the trees to wilt and die. The vector responsible for spreading the fungus from one elm tree to another is the elm bark beetle, a type of beetle that feeds on the inner bark of trees, creating galleries where it can also transport the fungal spores.
The correct answer to the question ‘Dutch elm disease is caused by a fungus that's spread by the bark type of which insect?’ is b) Beetle.