What impact do aphids have on the plants they infest?

Aphids are known as sap-sucking insects that can cause significant damage to plants. When they infest a plant, they pierce the plant's protective layers and feed on its phloem, which is the part of the plant that transports nutrients. This feeding can lead to several physiological changes in the plant.

The correct impact that aphids have on plants is the curling or distortion of foliage. This occurs because the sap-sucking action of aphids disrupts the plant's normal growth patterns. The stress and damage caused by aphids can lead to abnormal cell growth, resulting in curled leaves or distorted plant structures. Additionally, the excess sap they excrete can attract other pests and contribute to the development of mold or fungal diseases, further impacting the plant's health.

In contrast, the other choices do not accurately reflect the typical effects of aphid infestations. Rapid growth, wilted and brown foliage, or more vibrant flowers are not direct outcomes of aphid activity. Instead, aphids generally lead to stress and damage, manifesting primarily in distorted foliage.