What effect does the application of an insect growth regulator (IGR) have on flea treatment?

The application of an insect growth regulator (IGR) is designed to interrupt the normal growth and development of insects, specifically targeting their life cycle stages. In the case of fleas, IGRs primarily work by inhibiting the transformation of flea larvae into pupae. This prevents the larvae from maturing into the next life stage, which is critical for breaking the flea population cycle.

By effectively stopping larval development, the IGR helps reduce the overall number of adult fleas in the environment over time, as fewer larvae will develop into pupae and eventually into adult fleas. This long-term impact is essential in controlling flea infestations rather than providing immediate relief, which is more characteristic of adulticides that kill adult fleas directly.

The other options describe effects that are either unrelated to the specific function of IGRs or pertain to different mechanisms of action. For instance, IGRs do not kill adult fleas immediately, do not attract fleas away from pets, and do not disrupt flea feeding. These aspects highlight the specific function of IGRs in the lifecycle management of fleas, emphasizing their role in preventing future infestations rather than directly eliminating existing adult fleas.