Identify one type of insect growth regulator (IGR).

Methoprene is a well-known insect growth regulator (IGR) that mimics juvenile hormones in insects, effectively disrupting their normal growth and development processes. By interfering with the life cycle of the insect, Methoprene prevents it from maturing into an adult capable of reproduction. This makes it effective in controlling pest populations by reducing the number of new adult insects that can emerge.

In contrast, other options listed are not IGRs. Pyriproxyfen is indeed another example of an IGR, which functions similarly to Methoprene. Chlorpyrifos is an organophosphate insecticide that works by disrupting the nervous system of insects rather than regulating their growth. Bacillus thuringiensis is a bacterium used as a biological control agent against caterpillar pests but operates through a different mechanism by producing toxins that kill larvae, not by inhibiting their growth stages. Understanding these distinctions is crucial in pest management strategies.