How insect damage the plant​

Stem-boring insects can kill or deform individual stems or whole plants. ... Insects with sucking mouthparts, such as aphids, scales, leafhoppers, and true bugs, feed by sucking sap from plant tissues. This type of feeding can cause spotting or stippling of foliage, leaf curling, and stunted or misshapen fruits.

Insects can also cause injury to plants when they lay eggs (oviposit) into plant tissue. Heavy oviposition into stems can cause death or dieback of stems or branches on the plant. Dieback of the ends of stems or branches is often called flagging