Which of the following is a common sign of insect damage on plants?

Discoloration of leaves is a well-known indicator of insect damage on plants. When insects feed on plant tissues, they can cause changes in chlorophyll production, resulting in yellowing (chlorosis), browning, or other color changes in the leaves. This discoloration can be due to direct feeding by insects such as aphids or spider mites, who sap important nutrients and disrupt the plant's normal growth processes.

In contrast, excessive flowering usually indicates a plant's healthy growth and may be a response to favorable environmental conditions, not necessarily pointing to pests. Similarly, increased fruit production is an indicator of plant health and vitality, typically influenced by good growing conditions or proper pollination rather than detrimental insect activity. Rapid leaf growth might suggest a surge in nutrient availability or optimal growing conditions, and while some pests can affect growth rates, it's not a typical sign of damage per se. Overall, discoloration is a clearer and more direct sign of insect-related distress in plants.