The Timing of Deploying IGR Applications

Although the subject of this article is the use of Insect Growth Regulators (IGRs), its true purpose is to highlight the importance of knowing your target pest’s biology, particularly its reproductive cycles. This is a much different way of looking at pest situations. Most products we use have applications based on a target insect’s movement, harborage and feeding habits. Those same criteria hold true for IGR applications, but there is a required understanding of reproductive cycles to optimize the IGR effectiveness. This understanding has made IGRs a vital part of a true Integrated Pest Management (IPM) program, many times adding a layer of effectiveness that otherwise would not be achieved.

OH, THE TIMES WE LIVE IN! PMPs today are being asked to provide protection in more diverse pest situations than ever before. Fortunately, we have more tools at our disposal to manage these pests than at any time in the history of our industry. The product choices alone can leave your head spinning! With the right information and a little research, it’s possible to scientifically determine when to use which product for which pest in which situation for optimal results, which can be a complex equation.

Many times, through trial and error, we find what works for us and stick with it until it doesn’t work anymore, rather than identifying diminishing results and course correcting accordingly. This leads to frustration in the field and a loss of value and respect from your clients. The best PMPs have an understanding of target pest biology and habits, as well as how a particular product will affect the target pest. This information is impacted not just by the target species, but by the predictive temperatures and conditions of each season (although not necessarily at the time of application, but for upcoming days or weeks, depending on the target’s reproduction cycle).

A BIT ABOUT IGRs. IGRs are pesticides that affect insects with complete or incomplete metamorphosis and inhibit their ability to grow or develop as they naturally would. Different IGR configurations impact different life stages, ranging from eggs that are not viable to hatch; larval and pupal stages that do not progress; or adults that are sterile or have deformed reproductive organs. IGRs have been around for more than 50 years in agricultural use, but access to them for structural pest management purposes began in the late 1980s and early ’90s. At that time, Hydroprene revolutionized flea management by affecting other life stages of the flea that adulticides used before did not impact.

Since this discovery, PMPs continue to explore the impact that IGRs have on some of our toughest pest challenges, like German cockroaches, stored product pests, mosquitoes, filth flies and species of occasional invaders. Two common types of IGRs used in the structural pest management industry are juvenile hormones (e.g., methoprene, pyriproxyfen and fenozycarb) and chitin synthesis inhibitors (e.g., diflubenzuron, hexaflumuron and novaluron). Understanding just a bit about how each IGR type interacts with an insect can help you choose the right product for the right situation. Juvenile hormone IGRs harm the mutation and reproductive process, while chitin synthesis inhibitors affect the formation of chitin during molting, which can affect the ability to reproduce or even cause death.

IMMEDIATE GRATIFICATION…NOT REALLY. Today much of our society is an “I want it now” society of immediate gratification. But in the world of IGR applications, that isn’t the case. IGRs affect insects differently depending on life cycle development. Development time for insects is greatly impacted by environmental conditions such as temperature, moisture/humidity, food availability, etc. Several examples of this can be found in literature used to detail insect life cycles.

One need look no further than the pest management industry’s go-to standard, the NPMA Field Guide. As an example, the NPMA Field Guide states that for German cockroaches, the developmental time (egg to adult) usually varies from 54 to 215 days, averaging about 103 days. With variations in development based on environmental conditions and natural biology, the use of IGRs can become a bit of a challenge in setting expectations for treatments. IGR applications will not be evident until enough time has passed for the target pest reproductive cycle to have progressed; it may take weeks to see the impact of IGR usage on a pest population.

UNDERSTANDING BIOLOGY. IGRs can be utilized in more pest situations than may be immediately apparent. Experienced technicians usually identify appropriate applications for IGRs pretty easily. But newer technicians may not have accumulated enough experience to grasp the importance of understanding the target pest life cycle, which may limit their ability to make decisions on IGR applicability in the field. Reviewing IGR labels — which we should be doing anyway, but is worth saying again — may help to open their eyes to some of the possibilities, as well as training opportunities to explain and discuss pest biology and IGRs. This exercise will help technicians develop a thoughtful decision-making process. What follows is a review of common pests impacted by IGRs.

GERMAN COCKROACHES. Let’s start with the pest that has probably contributed to countless people retiring from our industry in despair, our nemesis, the German cockroach. Application of IGRs for German cockroaches can reduce egg hatch rates, stunt the molting process in nymphs, and leave adult reproductive organs deformed and unable to copulate (a sort of sick revenge for this prolific, difficult pest). IGRs for German cockroach management can be an effective tool, but a major drawback is that you and your clients are potentially conceding to activity for months while waiting for the existing adult population to expire. Remember, this is an “I want it now society” and many of your clients are not willing to wait for results. Although IGRs will impact pest populations over time, there is no substitute for digging and clawing to find the last cockroach to eliminate the problem right now.

FLIES, MOSQUITOES & OCCASIONAL INVADERS. This is a good one. Every tool in your arsenal needs to be pulled out to effectively manage filth flies like the house fly, blow fly and flesh fly, as well as small flies such as the phorid fly, drain fly and fruit/vinegar fly. IPM is a must in these situations and IGRs can be the missing component between success and failure. The practical challenges that are associated with filth fly and small fly management in some situations are immense. Elimination of the breeding site can be cost-prohibitive or not feasible for a variety of reasons. In some cases, we are lucky to have a client who works diligently to improve or maintain sanitation and implement exclusion efforts that will impact fly breeding sites or entry. The same applies to mosquito and occasional invader situations when standing water removal, vegetation management, exclusion or light management is requested by the PMP.

In these situations, it can be helpful to consider a more creative experiment. Take the house fly, for example. The breeding site is usually an exterior environment — dumpster area, processing waste, livestock waste, etc. When conditions are right, we know in many situations these breeding sites are going to be there day in and day out — they are predictive. However, when using IGRs for this type of house fly problem, most technicians hold off on applications until they see adult flies, effectively putting themselves behind the proverbial eight ball.

Instead, if you understand fly biology as it pertains to reproduction and temperature, and you know the pattern is present for a breeding site, you can treat with IGRs earlier. For individuals in the southern U.S., exterior IGR applications may begin in February or March, depending on weather patterns and temperature. Knowing that a house fly’s optimal life cycle temperature is between 70°F and 90°F will determine how and when different geographical locations in the country should begin applications and when it may be best to consider other alternatives.

As PMPs, leveraging tools like IGRs really requires strong knowledge in pest biology and innovative pest solutions from industry suppliers, and even an interest in keeping up with changing weather conditions to ensure we are making the right decisions — the right products and techniques for the target pest and its breeding cycles at the right, most effective, time.

Christian Wilcox, ACE, is the technical director for McCauley Services in Central Arkansas. He is a member of the Copesan Technical Committee, serves on the NPMA Technical Committee and is an ESA member.

Copesan is an alliance of pest management companies with locations throughout North America. To learn more, visit

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