Final answer:
The sap-sucking insects are likely aphids, which feed on the phloem sap and have a mutualistic relationship with ants. The incorrect statement about insect anatomy is that the trachea is part of the digestive system when it is actually part of the respiratory system.
Step-by-step explanation:
The likely identity of sessile, sap-sucking insects found on the underside of leaves in a forested area of South Carolina would be d. Aphids. Aphids are known to feed on the phloem sap of plants and are often found in colonies on the underside of leaves. They are protected by ants which in exchange collect aphid frass, establishing a mutualistic relationship. Aphids have stylets that penetrate into phloem tissue to feed on the sap.
The statement about insect anatomy that is false is c. The trachea is part of the digestive system. Insects have a well-developed digestive system, separate from their respiratory system, which includes the trachea. The trachea is connected to spiracles and is a part of the respiratory system that allows air to enter for gas exchange, not digestion.