original: Individuals have also illegally destroyed some trees and are suspected of introducing insect pests from Australia which attack the trees.
simplifications: Individuals have also illegally destroyed some trees and are suspected of letting loose insect pests from Australia that eat trees. Individuals are suspected of bringing insects from Austrailia to illegally destroy some trees. Some people have destroyed trees. They also might have brought pests from Australia which attack the trees. Individuals who illegally destroyed trees are suspected of introducing insects from Australia. People have illegally destroyed some trees. They are suspected of introducing insects from Australia to attack the trees. Individuals have also illegally killed some trees. They may have brought insect pests from Australia which attack the trees. People have also illegally destroyed trees. They are suspected of bringing insect pests from Australia which attack the trees. People have illegally destroyed trees and may have brought over insects that attack the trees. Individuals have illegally destroyed some trees. Those individuals are suspected of introducing pests from Australia. These pests attack the trees. Individuals have unlawfully destroyed some trees. It is believed that they are introducing insect pests from Australia which attack the trees.