C3 plants, which cannot photosynthesize at low CO2 concentrations, are more sensitive to changes in CO2 concentrations. Therefore, increasing CO2 concentrations could lead to preferential growth of C3 plants (which include most trees). C4 plants, including tropical grasses, corn, and sugarcane, will not be greatly affected by higher CO2 levels. As the climate warms, some insects that are currently confined to warm, tropical climates (e.g., the Anopheles mosquito which carries malaria), may expand their ranges poleward. The potato leafhopper is a crop pest that may expand northward into the United States Midwest.