Why are IGRs effective when applied at the 4th instar?

Why are IGRs effective when applied at the 4th instar?

• A. 4th instar so that it may upset the molting process at the pupal stage
• B. First instar to produce rapid results
• C. Egg stage prior to hatching
• D. Adult emergence after metamorphosis

Answer: (A)

IGRs work by disrupting the hormonal signals that control molting and metamorphosis in insects. They mimic juvenile hormone, so larvae stay immature and can’t complete their development into pupae and then adults. Timing is key: you want the larvae to encounter the IGR right as they’re about to molt to the next stage. The 4th instar is just before the molt to the pupal stage, so applying the IGR then blocks that final molt. As a result, the mosquitoes fail to reach the pupal and adult stages, greatly reducing adult emergence. Earlier instars may keep developing through multiple molts before the IGR takes effect, making the control less efficient, and targeting adults won’t prevent the ongoing development from larva to adult.

IGRs work by disrupting the hormonal signals that control molting and metamorphosis in insects. They mimic juvenile hormone, so larvae stay immature and can’t complete their development into pupae and then adults. Timing is key: you want the larvae to encounter the IGR right as they’re about to molt to the next stage. The 4th instar is just before the molt to the pupal stage, so applying the IGR then blocks that final molt. As a result, the mosquitoes fail to reach the pupal and adult stages, greatly reducing adult emergence. Earlier instars may keep developing through multiple molts before the IGR takes effect, making the control less efficient, and targeting adults won’t prevent the ongoing development from larva to adult.