What effect do insect growth regulators have on insects?

Insect growth regulators (IGRs) are substances that disrupt the normal development of insects, specifically by interfering with the processes involved in molting and reproduction. By mimicking hormones that are crucial for growth and maturation, IGRs can cause abnormalities in the insect life cycle, leading to issues such as sterility and improper molting.

When insects are exposed to IGRs, they may fail to shed their exoskeleton correctly or may not reach reproductive maturity. This disruption reduces their population over time, as the affected insects either die before they can reproduce or are rendered sterile, thus preventing future generations.

The other choices describe effects that do not accurately represent the primary function of IGRs. For instance, increasing reproduction rates, speeding up growth, and developing resistance to pesticides do not align with the known effects of insect growth regulators. Instead, these substances are specifically designed to control insect populations by hindering their growth and reproductive capabilities.