Final answer:
Insects with sucking mouthparts, such as aphids, cause plant injury symptoms including yellowing or browning of leaves, stunted growth, and deformation. These symptoms are because of nutrient and sap removal from the plant. Plants have various mechanisms to combat this, and some insects also aid in biological control of invasive species.
Step-by-step explanation:
Insects with sucking mouthparts, like aphids, cause specific types of plant injury symptoms. These symptoms include yellowing or browning of leaves, stunted growth, deformation, and sometimes the death of plant tissues. The damage is due to the removal of sap and nutrients from the plant, as well as potential transmission of plant pathogens. For instance, when aphids latch onto the phloem tissue and start siphoning the plant's sap, the plant may exhibit signs of distress. Similarly, insects like the American cassava mealybug, which have efficiently adapted their piercing mouthparts to extract sap, can lead to severe crop losses.
Multiple defense mechanisms evolved in plants such as spiky thorns or sticky substances to deter these insects, some of which are carnivorous plants like sundews and the Venus flytrap, that capture and digest insects to supplement their nutrient intake due to the nutrient-poor soil they often grow in. On the other hand, some insects are used in biological control projects to manage invasive plant species due to their ability to defoliate and suppress the growth of these plants, as evidenced by cases like the control of water hyacinth in Africa's Lake Victoria through introduction of weevils.