What is the effect of applying an Insect Growth Regulator (IGR)?

Applying an Insect Growth Regulator (IGR) primarily affects the developmental stages of insects rather than their adult forms. IGRs work by mimicking hormones that are crucial for insect development, and they disrupt the normal growth and morphogenesis processes. Specifically, when applied to pupa, they can prevent these immature insects from developing into adults. This interruption in the life cycle is what makes them effective in controlling insect populations without necessarily killing the adults.

While IGRs can have indirect effects on hatching and adult populations, their main function is to halt the development of larvae and pupae by interfering with their natural growth processes. This makes the correct answer focus on how IGRs keep pupae from maturing, thus helping to manage pest populations effectively while minimizing harm to beneficial insects and non-target organisms.