Which chemical class does not include neonicotinoids?

The correct choice is chitin synthesis inhibitor, as this chemical class is fundamentally different from neonicotinoids in its mechanism and target. Chitin synthesis inhibitors work by interfering with the production of chitin, which is a crucial component of the exoskeleton in insects and is essential for their growth and development. This class of chemicals effectively disrupts the lifecycle of certain insects by preventing them from forming new exoskeletal structures, ultimately leading to their death.

In contrast, neonicotinoids are a class of neuro-active insecticides modeled after nicotine, functioning primarily by targeting the nervous system of insects. They act by binding to nicotinic acetylcholine receptors, resulting in paralysis and death of the insect.

The other chemical classes mentioned—pyrethroids, phenylpyrazoles, and diamides—have different modes of action but are more closely related in their use as insecticides aimed at pest control in various contexts. Thus, chitin synthesis inhibitors stand apart from neonicotinoids, clearly distinguishing them as the correct answer in this context.