What effect do aphids have on plant foliage?

Aphids are small sap-sucking insects that feed on the phloem of plants. When they penetrate plant tissues to extract sap, they can cause significant damage to the plant's foliage. This feeding leads to abnormalities in the leaves, causing them to curl or become distorted. The curling is a direct response to the stress and damage inflicted by the aphid's feeding, as the plant tries to adapt to the injury and redirect its resources.

The other effects associated with aphid infestation, such as yellowing of leaves or the development of spots, may also occur, but the most characteristic and immediate impact on the foliage is the curling and distortion. This reaction is a clear indicator of aphid activity and can serve as a visible symptom for growers to notice and address potential pest issues promptly.