What chemical affects the normal molting and development of insects?

The correct choice is the option that identifies Insect Growth Regulators (IGRs) as the chemical that affects the normal molting and development of insects. IGRs are specifically designed to disrupt the hormonal processes that regulate the growth and development of insects, targeting their ability to molt effectively. By mimicking natural hormone behavior, IGRs can interfere with the normal lifecycle of pests, thereby preventing them from reaching maturity and reproducing.

IGRs are particularly beneficial in integrated pest management programs, as they can reduce pest populations over time while minimizing the impact on non-target organisms and beneficial insects. This mode of action is essential for controlling species that are particularly troublesome and can lead to long-term suppression of pest populations.

In contrast, other options like insecticides generally work by directly killing the insects rather than disrupting the developmental processes. Insecticidal soaps and horticultural oils operate through different mechanisms such as suffocation or dehydration, rather than hormonal interference. Therefore, the unique ability of IGRs to specifically alter the growth and molting patterns is what makes them the correct answer in this context.