Which of the following best describes external feeders?

External feeders are pests that primarily consume the outer surface of grains and processed products, often damaging them in the process. They typically feed on already damaged grains or other processed items, which makes them distinct from other types of pests that may develop within the kernel itself or only affect unprocessed goods.

The choice that identifies external feeders as those that feed on damaged grains and processed items accurately captures their feeding behavior. External feeders tend to exploit weaknesses in the grain or product, such as areas already affected by moisture or physical damage, which enables them to thrive while causing further degradation to the food source.

In contrast, other options suggest different feeding strategies. For instance, some pests that develop within kernels are termed internal feeders, and those that leave marks during larval development usually indicate a different lifecycle or feeding method. Additionally, the notion that external feeders appear only in unprocessed goods does not encompass their wider range of habitats, as they are often found in both processed and unprocessed items. Understanding this distinction is crucial for effective pest control and management strategies.