How do insect growth regulators affect insects?

Insect growth regulators (IGRs) are designed to interfere with the normal development of insects, specifically targeting their growth and maturation processes. They function by mimicking hormones that are crucial for molting and metamorphosis, essential stages in an insect's life cycle. By disrupting these processes, IGRs prevent immature insects from growing into adults, thereby inhibiting their ability to reproduce and thrive. This method of action is significant because it does not rely on killing insects outright but rather on preventing them from developing into their reproductive stages.

The other options do not accurately describe the function of IGRs. Promoting faster reproduction is contrary to what IGRs accomplish since they inhibit the maturation process. While these substances can affect various life stages of insects, they are particularly effective against immature forms and larvae, not just adults. Lastly, while some pesticides kill insects on contact, IGRs operate through a different mechanism, focusing on developmental disruption rather than direct lethality.