What type of insects are described as soft-bodied, pear-shaped, and often have horn-like structures?

The correct answer is indeed aphids. These insects are typically characterized by their soft-bodied appearance and pear-shaped bodies, which can vary in color from green, black, brown, or even pink, depending on the species and environmental factors. Aphids are commonly found on the undersides of leaves, where they feed on plant sap, and they are known for their ability to reproduce rapidly.

The horn-like structures, often seen on some species of aphids, are actually tubercles that can resemble horns; these structures can assist in the insects' defense against predators. Aphids play a significant role in plant health, as they can transmit various plant viruses when feeding.

In contrast, scale insects have a harder exoskeleton and are often flat and scale-like, mealybugs are typically covered with a white, waxy coating and are not particularly pear-shaped, and whiteflies, while also soft-bodied, have a more rounded shape and are distinguished by their white, powdery wings. Each of these other insect types has unique physical characteristics that set them apart from aphids, making them easily identifiable.