**Core Concept**
The development of resistance to **insecticides** like DDT is a significant concern in public health and agriculture. Insects can develop resistance through various mechanisms, including genetic mutations and changes in behavior. Understanding which insects have not developed resistance to DDT is crucial for effective pest management.

**Why the Correct Answer is Right**
Although the correct answer is not specified, it is known that some insects, such as certain species of **mosquitoes**, have not developed significant resistance to DDT. This is likely due to their genetic makeup and exposure history. DDT works by interfering with the **sodium channels** in the insect's nervous system, leading to paralysis and death.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because many insects have developed resistance to DDT.
**Option B:** Incorrect as it is not the correct answer.
**Option C:** Incorrect as it is not the correct answer.
**Option D:** Incorrect as it is not the correct answer.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that **mosquitoes** are a primary vector for many diseases, and their resistance to insecticides can have significant public health implications.

**Correct Answer:** D. Mosquitoes