IGRS: A Refresher Course

At a time when customers demand instant results for their pest control dollars, slower-acting methods of pest control, such as insect growth regulators, are perhaps not the first products that come to mind.  After all, this class of products, which works by interfering with insects’ development, doesn’t immediately kill pests.

But this time-tested, dependable technology offers some unique — and “green” — benefits not found in other products. Toward that end, here’s a primer on how IGRs work, how they can be used, and in what situations they hold the best potential for success.
 
HOW THEY WORK. IGRs, or insect growth regulators, have been around for some time, the first of which were introduced in the 1970s. There are two basic types of IGRs used in the structural pest control industry: juvenoids and chitin synthesis inhibitors.

The first type, juvenoids, or juvenile hormone analogs, work by interfering with the normal growth and development of insects. In particular, immature stages of insects that have been exposed to juvenoids, never develop properly and so they cannot reproduce or develop into biting adults. “These are sterilizing-type agents, where they keep the insects in an amateur state,” explained Dr. Gary Bennett, professor of entomology and director of the center for urban and industrial pest management at Purdue University.

For instance, when immature cockroaches are exposed to IGRs, explained Bennett, they may never develop into adults or be able to reproduce. Adult cockroaches exposed to IGRs may not be able to produce viable eggs, he added. And exposed eggs may not hatch properly. Likewise, freshly laid flea eggs in a home or mosquito larva in a pond will never become biting adults after having been exposed to IGRs. “It just disrupts the whole growth and development process,” Bennett said.

The second type of IGRs, known as chitin synthesis inhibitors, primarily target termites as the active ingredient in termite baits. These work by disrupting insects’ molting process, causing immature insects to develop malformed cuticles that effectively prevent molting. Ultimately, the insects are killed while attempting to molt. This is a primary distinction from juvenoids, which generally don’t kill insects but simply keep them in a prolonged immature state. Typically chitin synthesis inhibitors are carried by worker insects back to the colony where they are shared, and ultimately the whole colony is affected.
 
BROAD RANGE OF PESTS. Experts say IGRs have an important place in controlling a wide variety of insects. A study of the labels of currently available IGRs will show you that a great number of insects can be treated with IGRs, particularly cockroaches, fleas, mosquitoes, fire ants, stored product pests, drain flies and bed bugs.

Dr. Bob Cartwright, technical manager for Syngenta Professional Pest Control, says IGRs are particularly appropriate for those insects that have displayed resistance. “The real strength of the IGRs (is for) the insects where resistance is consistently a concern,” he said. He notes that cockroaches, fleas, flies and mosquitoes all are very proficient at overcoming insecticides.

And Dr. Robert Suranyi, entomologist for MGK, notes that IGRs may be a relatively old group of chemistries, “but at the same time it’s really a 21st century chemistry,” primarily because you need to understand pests’ biology to use them correctly. Furthermore, Suranyi explained, insects are very sensitive to the effects of IGRs. “You really need a very small amount of interference to create this avalanche of end result,” Suranyi said.

Stoy Hedges, director of technical services at Terminix International, Memphis, Tenn., points out Terminix has used IGRs in various segments of its business for years, particularly in flea treatments and commercial cockroach control, as well as for stored product pests and mosquito control.

IGRs are particularly important for flea control, Hedges notes, since they prevent immature stages becoming biting adults. With cockroach infestations, Hedges said, IGRs are used primarily for serious situations in commercial accounts.

And while chitin synthesis inhibitors can be used as standalone treatments, as in the case of termite baits, juvenoids are often used alongside other insecticides. Toward this end, Bennett points out PCOs can maximize their success by using both. “A lot of times it takes an insecticide along with the IGR to get the job done,” Bennett said. He noted that insecticides help to knock back the adult populations, while IGRs work on any future populations that aren’t reached by the insecticide.

This is a particularly successful strategy for serious cockroach infestations in commercial situations. Without IGRs, Bennett notes, heavy cockroach infestations require repeated insecticide treatments. “You won’t get all of the cockroaches, whether they are adults or immature forms, because large populations tend to be scattered in walls,” he said.

But he notes, if you incorporate an IGR, “you may be able to apply an insecticide and not have to do any additional insecticide treatments at all.” In effect, the population is not able to reproduce itself once IGRs are thrown into the mix. Additionally, IGRs can also be used alone for maintenance purposes as well, Cartwright points out, for intervening at a time when you’re not putting out an adulticide.

Another major advantage of IGRs is that they have low toxicity when it comes to mammals, birds, fish and other nontarget animals. Plus, IGRs offer a long residual life, anywhere from one month to six weeks, Bennett said. “You may have to go back three months later, but at least you’re not applying insecticides every other week,” Bennett said.

For mosquitoes, Bennett notes, professionals may be able to use an IGR by itself, depending on what’s being treated. “If you’re treating a pond or ditch with an IGR and then you don’t have any adults coming off,” he said, “in that case, you’ve solved the problem.”

Using IGRs for mosquito control offers big benefits, notes Doug VanGundy, director of specialty product development for Central Life Sciences, based in Dallas. By preventing biting adults from coming off, adult foggings aren’t required, and so the amount of insecticide required is greatly reduced.

Even ant control has been boosted with IGRs. David Naffziger, senior research scientist for Whitmore Micro-Gen Research Laboratories, based in St. Louis, points out ant baits incorporate IGRs that are designed to be spread to and sterilize the queen.

Ed Johns, regional sales manager with Paragon Professional Pest Control Products, Memphis, Tenn., said IGRs should be used wherever possible. “If a target insect is on the label, I really suggest that you ought to be putting IGRs in with your residual,” he said. Not only does this keep the juvenile stages from maturing, Johns notes, but it also lasts a very long time. “I think IGRs work on so many insects that they are probably underutilized,” Johns added.

To make sure the IGRs are having an effect, say in cockroach control, insects can be monitored using traps and examined, VanGundy notes. Exposed insects might display such abnormalities as twisted wings. PCOs should also see a reduction in the number of cockroaches they trap.
  
RISING POPULARITY. Regarding cockroaches, mosquitoes and fleas, the use of IGRs has held steady and perhaps even grown, experts say.

Even so, Cartwright notes, there are a few reasons why IGRs may have fallen off some PCOs’ radar screens. For one, he says, much of the research on IGRs is at least 10 years old. Furthermore, there haven’t been any new IGRs introduced as of late. But, he notes, IGRs continue to hold great potential for the industry. “As we move toward lower impact, you’re going to see a lot more interest in IGRs,” Cartwright said. “IGRs shine when they’re used in combination with other good products.”

Naffziger notes IGRs stand a good chance of coming back into the spotlight, particularly because of their wide use potential. For one, he says, the industry may want instant gratification, but that’s not how IGRs work. “The growth regulator is like a disease spreading through the colony and killing it, and you want it to be slow,” he said. Furthermore, cockroach baits were initially so successful, that IGRs weren’t being used along with them. But now, he says, gel bait aversion has cropped up. Incorporating IGRs in with cockroach baiting, he notes, may enhance and preserve that treatment strategy.

And VanGundy says Central Life Sciences has seen an increase in the use of IGRs in the last five to 10 years. “It’s my personal opinion that our sales have increased with the IGRs. I would imagine the industry overall is using more insect growth regulators.” The company’s IGRs are labeled for control of cockroaches, stored product pests, drain flies, fruit flies, bed bugs, fleas, mosquitoes and ants, all pests which have shown growth in recent years.

VanGundy also says IGRs fit well with the demand for more green approaches to pest control because they’re of a low toxicity compared to conventional chemistries and they provide a long residual. “I think more PCOs recognize that IGRs can be a real benefit to them,” he said.

Johns at Paragon agrees there seems to have been an increase in the use of IGRs. “I believe that when IGRs first got started they were primarily for fleas, then for fleas and cockroaches, and then it really exploded into including ants.” Now, he says, IGR labels have been expanded to include more use sites as well as other insects, such as food processing pests.

KEY TALKING POINTS. Considering the complexity of how IGRs work, and the fact that juvenoids don’t actually kill insects, care should be taken in how IGRs are explained to customers. With fleas, says Hedges, PCOs should explain that the goal is to interrupt the life cycle, preventing them from becoming biting adults.

And with cockroaches, says Hedges, professionals should discuss the long-term benefits IGRs will provide, namely population reduction. “The population is not as capable of exploding as it would be in the absence of IGRs,” he notes. With cockroaches, customers will have to be told that they may see some adults, however they may look abnormal, and they won’t be capable of reproducing.

VanGundy said PCOs should provide a simple explanation of how the products work, namely that it prevents reinfestation by preventing reproduction.

And Joe Eger, a field biologist with DowAgrosciences Urban Pest Management, notes that homeowners should be made aware that IGRs tend to be very selective toward insects, and have low toxicity to mammals and nontarget insects. “I think the fact that they have a high differential between toxicity to insects and to people and their pets is a key point,” Eger said. Further, he noted, “the place where they really stand out, where they’re a better choice, is any kind of sensitive situation.”
 

When and Where Do You Use an IGR?
Insect Growth Regulators (IGRs) are ideal for use with adaptable insects that have a reputation for resistance. Here are some pest-specific examples on the where and when of using IGRs:

Cockroaches. Cockroaches are notorious for resistance and IGRs are a great defensive weapon. When baiting for cockroaches, incorporate an IGR into your program and apply near suspected harborage areas, behind appliances, under sinks and cabinets, etc. This will interrupt the growth cycle of immature roaches, which forage less to reach your bait or could be the offspring of a mature, resistant roach.

Ticks. Many customers reported a surge in tick calls this year because of a wet spring and mild winter. Ticks can lay dormant for a long period of time. Using an IGR in tick-prone areas can prevent the young from developing into adults.
Treat for ticks similarly to the way you do mosquitoes by looking for lush, shaded areas. Low-lying shrubs or branches and tall grasses are likely tick harborages. Mix an IGR with an adulticide and spray the brush just like you do for mosquitoes, only instead of targeting the waist to head level of brush, target waist down levels of underbrush.

Fleas. In most indoor flea treatments a full carpet spray isn’t justified. Instead, mix your IGR with an adulticide and apply in two foot circles around the areas that pets frequent. Work with your customers to identify these locations. Don’t forget to treat outdoors if necessary.

Crickets. Many customers have recurring cricket problems at the same time every year. If this is the case with one of your accounts, use an IGR to treat cricket habitats at the first adult sighting. This will stop population growth by reducing the number of reproducing crickets. You can mix with an adulticide to control mature crickets.

Commercial Kitchens. An IGR is a great tool in a commercial kitchen as a means to manage cockroach populations. Treat floor drains, behind cooking equipment, and under sinks and prep areas. Mix with an adulticide for best results and be sure to check labels to make sure you are using products that are labeled for food-handling areas.

IPM Programs. With increasing interest in lower environmental impact (LEI) pest control, Syngenta has seen growth in the sales of our IGR. As a growth hormone mimic, an IGR is a great fit for sensitive accounts and can easily be incorporated into LEI programs. Recently we have seen customers using an IGR in IPM ant programs. Prior to entering heavy ant season, they will run an IGR on their routes to suppress population levels. This reduces the pest pressure when heavy season comes along, allowing the customer to use lower impact products effectively. — Dr. Bob Cartwright, technical manager, Syngenta Professional Products. Syngenta’s IGR, Archer is often paired with Demand CS with iCAP technology or Optigard Flex insecticides for various pest control programs. Visit www.syngentapmp.com for more information.

To Discuss with the Homeowner
Since IGRs differ from insecticides that kill pests on contact or via transference,
PCOs should provide a simple explanation of how the products work, namely that it prevents reinfestation by preventing reproduction. Here are some tips to get the conversation started:
• Explain that eggs hatch in one to 10 days. Larva stage lasts one to five weeks. Cocoon/pupa stage runs up to four weeks and thhen fleas emerge as adults. Adult fleas make up only one percent of infestations.
• At time of treatment, fleas in the pupa stage are very resistant to insecticides. Homeowners may continue seeing adult fleas emerge for a two-week period after Precor application. The fleas will die soon, making callbacks unnecessary.
• Identify “hot spots” for treatment: places where pets like to play, rest, sleep and hide.
• Encourage vacuuming 24 hours after application and then every three to four days for two to three weeks to get any pre-adult fleas to surface in order for IGRs to control them.
• Remind homeowners to remove all pets from the premises on the day of application.
• Apprise homeowners of the appropriate waiting period before they and their pests can re-enter house (usually only two to four hours or until carpets are dry). Source: Central Life Sciences “Precor: Get Down with Fleas CD.”  Central Life Sciences’ Precor IGR, which  has the active ingredient S-Methoprene, halts development of pre-adult fleas. Visit www.zoecon.com for more information.

IGR Best Practices
IGRs are most effective when used as part of an IPM system that is built on a foundation of hygiene, exclusion and monitoring. Since IGRs are most active against juvenile life stages and do not kill adult insects, they are slow to show results when used alone. Since most of your customers want to see immediate results, an application of an adulticide along with the IGR is the best practice for delivering immediate results. A spray mixture of a pyrethroid and an IGR or fogging with a mix of pyrethrum plus an IGR will kill existing populations and lay the foundation for long-term elimination of the insect colony.

Regarding how often the PCO should apply IGRs, monitoring is used to determine when it is time to retreat. Evaluation of insects caught in traps will provide the information a PCO needs to determine when to reapply an IGR. This is important since an IGR will outlast most pyrethroids and similar “adulticide” chemistries.

Here’s a rule of thumb: as long as 80 percent of the insects trapped are showing the symptoms commonly associated with an IGR (such as deformities), additional treatment is not required. When less than 80 percent of the insects trapped display IGR symptoms, it is time to re-apply an IGR.

Following these practices ensures that the reproductive potential is reduced and the re-infestation cycle is broken. Source: Kevin Caskey, MGK. MGK’s NyGuard IGR Concentrate is an emulsifiable insecticide concentrate containing an IGR. Visit www.mgk.com for more information.

The author is a frequent contributor to PCT magazine.