What parts of the plant do adult billbugs feed on?

Adult billbugs primarily feed on the stems and leaves of plants. This feeding behavior can lead to significant damage because they tend to bore into the stems, which can interrupt the plant's nutrient and water transport systems and ultimately weaken or kill the plant. This part of their feeding habit is crucial, as it not only affects the overall health of the plant but also makes it more susceptible to secondary infections and pests. Understanding the feeding habits of adult billbugs is essential for effective pest management strategies.

The other choices, while they mention different plant parts, do not accurately reflect the primary feeding behavior of adult billbugs.