09/13/2024

Insect Growth Regulators a Small Price to Pay for Added Value

Richard Kramer, BCE, Kramer Pest Management & Consulting

In my experience, insect growth regulators (IGRs) are a misunderstood and therefore underused tool in our industry.  A better understanding of how they function can illustrate how they add value to pest management strategies.

IGRs were developed in the 1960s mainly because of research looking for alternatives to traditional pesticides that was influenced by Rachel Carson’s book Silent Spring.  The investigations into green insect control chemistries was the goal of co-inventor of the birth control pill, Carl Djerassi. He founded Zoecon to begin the search for alternative pesticides based on insect neuroendocrine factors.

Further understanding of the role of ecdysone (molting hormone) and juvenile hormone led Zoecon researchers down the path to chemical synthesis of analogues of these molecules. In 1968, after many trial and error evaluations three compounds (methoprene, hydroprene, and kinoprene) emerged as potential active ingredients for commercial development.

Methoprene became the lead compound as it showed the most promise on a broad spectrum of insect pests. Public health pests were evaluated and targeted due to the continued existence of immatures, i.e., larva continued to feed on crops etcetera

Three types of IGRs were developed:

• Juvenile hormone analogs (JHAs) (methoprene, hydroprene, and kinoprene): synthetic copies of naturally occurring insect bio-chemicals; registered by USEPA as bio-pesticides. These products work at a molecular level and readily spread throughout the treated zone affecting target insect populations.
• Juvenile hormone mimics (JHMs) (fenoxycarb and pyriproxyfen): molecules that have no similarity to biochemicals but have IGR activity; they are not considered biopesticides and are registered by USEPA’s Office of Pesticide Programs.
• Chitin synthesis inhibitors (CSIs) (diflubenzuron and lufenuron): interrupt the molting process by inhibiting chitin synthesis; they are not considered biopesticides and are registered by USEPA’s Office of Pesticide Programs.

IGRs interfere with the development of certain insects. Insects have juvenile hormone present during larval and nymphal development but it decreases as they mature to pupae and adults. The presence of JHAs and JHMs during final molting prevents normal development into adults.

Eggs are affected by disrupting embryo development and newly laid eggs can be affected when laid on a treated surface. Activity occurs during the last larval or nymphal stage, however extra instars or life stages may occur. In hemimetabolous insects, such as cockroaches (gradual metamorphosis), nymphs molt into adults no longer able to successfully mate.

The IGR spectrum of activity includes:

• JHAs
  • Methoprene has stronger activity on insects that pupate, e.g., fleas, mosquitoes, ants, moths, flies, etc.
  • Hydroprene has stronger activity on insects that don’t pupate, e.g., cockroaches, bed bugs, etc.
• JHMs have similar activities on insects as the JHAs.
• CSIs have activity on a wide array of insects but are most notably used for termites.

JHAs are generally low order toxicity and can be used in a larger number of sensitive habitats, such as aquatic sites and food prep and food handling areas. Methoprene has an LD₅₀ > 34,560 and has an exemption from the requirement of food tolerances.

How can IGRs be used:

• Used alone in very sensitive accounts, such as schools, hospitals, LEED buildings – activity is slow, and you must wait for the existing adult population to die of natural causes.
• Tank mixed with other insecticides. This enhances the effectiveness of both products providing a fast reduction of pests. IGRs keep untreated individuals from reproducing and keep invaders from developing a new infestation.
• Because IGRs perpetuate the immature stages of insects (nymphs and larvae) it stimulates increased feeding activity on baits.

The advantages of using IGRs include:

• Effective long term pest control
• Ideal for sensitive areas
• Target pest specific
• Can be tank mixed with insecticides
• Helps prevent re-infestations
• Broad spectrum of activity
• Long residual
• REDUCES CALLBACKS