Use of Insect Growth Regulators: Back to the Future
By: Bob Cartwright, Technical Manager, Syngenta Professional Pest Management
Insect Growth Regulators (IGRs) are a powerful tool for Pest Management Professionals (PMPs) in their ongoing fight against insect pests. Of the pest control products used today, IGRs have been on the market longer than the majority of other types of products.
First discovered in the 1970s and 1980s, the group of products known as IGRs include several chemical classes with different modes of action. While the modes of action differ, the common similarity is that all IGRs act on an insect’s growth cycle. Some affect the molting process (Chitin Synthesis Inhibitors) while others mimic juvenile hormones (Juvenile Hormone Analogs), which controls the insect maturation process.
While a range of different chemistries are available to PMPs to help them do their jobs, the majority impact an insect’s nervous system. IGRs offer distinctly different modes of action against insects compared with other insecticides. Using insecticides with different modes of action can be an effective means to delay or avoid insecticide resistance. Some notable insects that have been shown to gain resistance to insecticides include fleas, cockroaches, mosquitoes, flies and bed bugs.
Because IGRs primarily affect the growth of insects, they are slower acting and the effects may be less noticeable than with other insecticides. This characteristic alone has lead some PMPs to abandon IGRs in favor of faster-acting insecticides that leave a more visible insect control. Effective usage of IGRs often requires the PMP to educate the consumer by explaining in simple terms how IGRs work, their relative slow action and their benefit to managing pests over the long term.
The benefits of IGRs include:
- Effective means to manage resistance to other insecticides
- Considered low impact
- Can be used in sensitive areas
- Low hazard, low mammalian toxicity
Types of IGRs
Mode of action should always be considered when choosing a product along with the other factors that go into a PMP’s decision making process. When comparing the two key IGR groups, Juvenile Hormone Analogs (JHAs) and Chitin Synthesis Inhibitors (CSIs), juvenile hormone-based products are the focus for general pest control, while the CSIs are typically used in the control of termites.
CSIs which include: lufenuron, noviflumuron, hexaflumuron and diflubenzuron are currently only registered for PMP use as termite control products. Termite bait products that contain CSIs are well established tools in termite management. Since the focus of this article is on general pests, the Juvenile Hormone Analogs will be the primary topic discussed.
Juvenile Hormone Analog IGRs
Products that are JHA IGRs include:
- Pyriproxifen (Archer®) – indoor and outdoor use, multiple pests
- Methoprene (Precor®) – indoor, flea
- Hydroprene (Gentrol®) – indoor, cockroach
- Fenoxycarb (Award®) – fire ant bait
Target Pests for JHA IGRs:
- Flies (house, horn, drain flies)
- Stored product pests (flour beetles, dermestids, grain moths, etc.)
The Effectiveness of JHA IGRs
A significant body of scientific work has gone into researching the effects and efficacy of JHAs. JHAs work by affecting the level and binding of juvenile hormone in insects. The juvenile hormone is an essential compound used by insects to regulate development during the immature stages and also has a role in egg and sperm production and development in adult insects. The juvenile hormone isn’t found in mammalian systems; this explains why JHA effects are specific to insects and their relatives. While the direct effect of these compounds seems to be affecting the enzyme that results in the natural decline of juvenile hormone in an insect, other more subtle effects of these compounds on the insect have been discovered. In addition to affecting the development of immature insect pests, pyriproxifen (Archer) has been shown to affect adult insect pests by:
- Accelerating water loss and reduced ability to attach to host in adult ticks, thereby increasing mortality
- Reducing egg prod