What substance do aphids produce?

Aphids are small sap-sucking insects that produce a sugary substance known as honeydew as a byproduct of their feeding process. When aphids feed on plant sap, they extract nutrients but excrete excess sugars in the form of honeydew. This substance can accumulate on the surfaces of leaves and can attract other pests, such as ants, which farm aphids for this sweet reward.

In contrast, pollen is a reproductive element produced by plants, not insects. Insecticide refers to substances used to kill or control insects, which does not relate to aphids' natural production. Nectar is a sweet fluid produced by plants to attract pollinators, not a product of aphid activity. Therefore, honeydew is the correct answer, as it directly relates to the specific behavior and digestive process of aphids.