Which of the following biological control agents is commonly recognized?

The correct choice is ladybug, which is well-known as a biological control agent in agriculture. Ladybugs, or ladybird beetles, are particularly effective in controlling aphid populations, which can be detrimental to various crops. By preying upon these pests, ladybugs help reduce the need for chemical pesticides and promote a healthier ecosystem within agricultural fields.

Other options, while they may assist in pest control, are less commonly recognized or utilized as primary agents. Spiders can capture various insects but do not specifically target agricultural pests in an effective or predictable manner. Wasps, particularly parasitic types, can also contribute to biological control, but they are not as universally recognized for this role as ladybugs. Ants tend to farm aphids rather than prey on them, which does not contribute positively to pest control in the way ladybugs do. Thus, the ladybug stands out as a quintessential biological control agent in crop management.