What do insect growth regulators primarily block in immature insects?

Insect growth regulators (IGRs) are chemical substances that mimic or disrupt the hormones involved in the growth and development of insects. They primarily target the processes necessary for normal development and molting, which are critical stages in an insect's lifecycle. By interfering with these hormonal signals, IGRs prevent immature insects from growing into adult forms, thus blocking their normal physical and physiological processes.

This mechanism is particularly effective because it disrupts the delicate balance of hormones that instruct insects when to molt and develop. As a result, IGRs are used in pest management to control populations of immature insects, limiting their growth and reducing future reproduction rates. This strategy helps manage pest infestations by targeting their lifecycle stages, ultimately leading to a decline in their numbers without the need for more hazardous chemicals.

Other options such as blocking reproductive systems or feeding abilities are not the primary actions of IGRs. While they may have some effects on those aspects in a broader pest management context, the core function of IGRs is their specific impact on developmental processes. Similarly, while communication methods might be affected by other pest control strategies, IGRs do not primarily operate through that mechanism.