What effect does an IGR have on flea pupae?

An Insect Growth Regulator (IGR) is specifically designed to disrupt the normal development processes of insects, including fleas. When applied to flea pupae, the IGR interferes with the hormonal balance necessary for metamorphosis. This disruption prevents the pupae from developing into adult fleas, effectively halting their life cycle.

By preventing the development of the pupae, IGRs can significantly reduce the flea population over time. They do not kill the pupae outright; rather, their action is geared towards inhibiting growth and maturation into the adult stage, which would lead to further reproduction and infestation. This mechanism is particularly useful in pest management as it targets the growth stages without causing immediate mortality, allowing for a prolonged effective control strategy.

In contrast, other options that suggest immediate death, increased survival, or no effect do not accurately reflect the function of IGRs. IGRs are specifically formulated to disrupt the developmental stages of pests rather than provide direct lethal effects.