Gentrol may make bed bugs worse?

by nobugsonme on March 26, 2007 · 19 comments

in bed bug treatment, bed bugs, pesticides

Hi all,

An anonymous entomologist and PCO who reads the blog has clarified for me the issues around Gentrol (an Insect Growth Regulator commonly used against bed bugs, by PCOs: IGRs are supposed to halt growth, which should cut off reproduction).

But my source tells me this:

In recent research, the results seem to indicate that the
use of Gentrol is at best not producing the
expected positive results in regard to overall
bed bug reduction. In fact in this study it seems
that the use may result in a long term increase.

But again this is one study and the unexpected
outcome itself still needs to be studied.

It hadn’t occurred to me that Gentrol could be not just ineffective, but might also make your bed bug problems worse. Still, the jury is still out, and we need more information.

I would not panic if your PCO uses Gentrol, but I also would not start lobbying for it if they don’t.

1 jessinchicago March 26, 2007 at 9:02 pm

As a side note, I recently read something (cannot remember where or what) that indicated Gentrol might actually cause bedbugs to increase activity and lay more eggs, at least directly following initial exposure. This was explained as a normal effect of the product, as the stimulation of procreation actually leads to more bugs exposed to the intended effects in a shorter amount of time- before the product is rendered ineffective over time. Also, I believe I read that Gentrol stimulates the behavior of roaches and other targeted insects as a method of control as explained above. I wonder if this is what the expert is referring to, or if it’s something else altogether? Interesting…

2 S. March 27, 2007 at 10:17 am

My PCO had been to a conference where a study like this was shared. I don’t recall the details either, but it was a similar outcome – at best, nothing happens; at worst, they actually reproduce more. I still think the theory of an IGR is sound, but maybe Gentrol isn’t quite ready for prime time.

I hope the ‘anonymous expert’ will keep us posted if this changes!

3 willow-the-wisp March 30, 2007 at 8:48 pm

I had heard thet growth regs didn’t work on bb’s, then I heard they prevent adult state of bed bug.
naybe this is whewr I should have put it:
who knows

4 nobugsonme March 30, 2007 at 8:54 pm

The intention is to prevent their growth from nymph to adult. But the study says this may not happen. It may not be effective, and may have the opposite effects.
Hopefully more studies will follow.

5 anonymous March 8, 2008 at 1:08 am

The study was never officially published, but here is an excerpt from it dated December 2007. Note, the study was actually supported by Zoecon (the company that manufacturers gentrol IGR)! Below is the excerpt from the study. Please understand that since the study has yet to be “published”, I must keep my anonymous status at this point in time…

The following paper was presented at the Annual Meeting of the Entomological Society of America on 13 December, 2006: The effects of hydroprene (9%) on the common bed bug (Cimex lectularius (L.) development by David J. Moore, Dini M. Miller (VPI).

Note: the study was supported by Zoecon.

Summary of the study:

The study was targeted at third instar nymphs of bed bugs using the labeled rate of Gentrol. The third instar stage was selected because this stage was supposedly the most susceptible to the effect of hydroprene. Gentrol was applied to filter paper strips, which were placed into small glass vials containing third instar bed bugs. Three filter paper strips (one treated and two untreated) were placed into each vials for the Gentrol treatment whereas the control treatment received three untreated paper strips. After 2 weeks of continuous exposure, one untreated filter paper strip was replaced with a fresh Gentrol treated paper to mimic application recommendation by Zoecon in the Gentrol treatment.

No developmental effects were evident in the nymphs until the commencement of nymph-to-adult molt. Sixteen percent of bed bugs died during mid-molt and an additional 18% died due to incomplete sclerotization of the adult cuticle. Surviving adults were examined for morphological defects. Males exposed to Gentrol showed a 25% reduction in the length of the male genitalia and the deformation of female genetalia was also observed. Potential reproductive effect of Gentrol exposure was examined by paired crosses of the survivors (control vs. treated) by sex. Treated females mated with treated males produced ~15.3 eggs, treated males mated with untreated females produced ~11.5 eggs whereas untreated males mated with untreated females produced ~7.9 eggs. Egg viability was > 95% in all crosses. The study showed that exposure to Gentrol significantly improves the fecundity of bed bugs, and thus the effect of Gentrol on the overall level of control is actually negative.

6 mangycur March 8, 2008 at 1:14 pm

Anonymous, that is fantastic. Where can we get a copy of the full study? Can I find it by googling?

7 persona-non-bugga March 9, 2008 at 5:30 pm

Anonymous, thank you so much for sharing this.

Do you expect the study will eventually get published?

To any entos: are there other insect growth regulators that have been shown to be effective against bedbugs? Thanks in advance for any responses.

8 Natalie April 1, 2008 at 9:56 am

i was treated with Gentrol and 5 days later I have found several BB’s on my person AND a ton of Roaches that were in hiding before!!!

9 nobugsonme April 1, 2008 at 7:54 pm


The jury is still out on whether Gentrol helps or makes bed bug infestations worse.

I think I can say, though, that whatever negative effects it might have would not have occurred within five days.

It is more likely that something your PCO used to treat (perhaps a flushing agent) drove bed bugs and roaches out of hiding. This does not mean their population has increased, but rather means you have a better shot at killing them. Hiding bugs do not die from pesticides. Coming out and crossing poison is the way they will be hit.

So, sorry this is unpleasant, but don’t assume the treatment was bad. If you want more feedback, come to the forums (button above). In any case, make sure your PCO re-treats in about 2 weeks.

10 Entomologuy July 16, 2008 at 6:35 pm

Pyriproxifen has shown some real promise. I’ve heard the same disappointing news regarding Gentrol IGR from fellow PCOs at a seminar in Portland just a few months ago, and Michael F. Potter, one of the speakers, covered resistance issues as well (though I don’t remember if he discussed IGRs or just insecticides).

Gentrol doesn’t prevent nymphs from reaching the adult stage, it just inteferes with their development so that when nymphs reach the adult stage, they are not reproductively viable. Hence the distortions in the exoskeleton.

I would like to know if any research has been done regarding the use of chitin inhibitors on bedbugs. Anyone?

11 hopelessnomo July 16, 2008 at 8:19 pm

Interesting question, Entomologuy, sent me looking. I found references here to someone whose infestation was treated, in part, with Starycide (triflumuron) in a European country and it seems that a triflumuron product, a dust, was mentioned in a draft of the first edition of the Australian CoP, so it’s possible they’re used for bedbugs in other countries?

I’m not sure I understand the fine distinctions between the chitin inhibitors and juvenile analogs, so I hope someone will elaborate. And, is there an issue with bedbugs not “sharing” because they’re not properly social insects or does it not matter?

Also, just fyi, there’s a new study on methoprene being presented at ICUP by Richard Naylor: (We know Naylor here because of his laundry temperature experiments.) Anyway, I thought methoprene (but not hydroprene; they’re both juvenoids I just learned) was found effective against bedbugs in the 70s. I hope this new study sheds more light.

12 hopelessnomo July 22, 2008 at 12:01 pm

And apparently, methoprene is promising:

Work at Sheffield University by Richard Naylor using the juvenile hormone analogue (S)-methoprene had produced good results. Better known for its activity with Pharaoh ants, this IGR offers a way forward. Recognizing the length of time it requires to achieve control, its use combined with a residual spray, such as bendiocarb, proved a talking point, especially as the IGR may heighten bed bug susceptibility to the conventional insecticide.

13 ANDY July 22, 2008 at 7:59 pm


14 ANDY July 22, 2008 at 8:03 pm

I stand corrected it is called cy kick cs

15 nobugsonme July 22, 2008 at 10:42 pm

Lethal for bed bugs, Andy?

16 Tom September 29, 2008 at 7:16 am

An IGR is effective when used in conjuction with an adulticide and the nessasary steps taken.

not a silver bullet

17 upstate November 8, 2008 at 5:43 pm

Hello all. My POC has used Gentrol along with a residual pesticide — he treated twice, and each time the incidents of bites disappeared. After the first spray, though, in about 2 weeks, I discovered bites again.

This is the first that I’ve heard that Gentrol could make the problem worse!!! Has this study finally been published? Is there any more news since this information came out at the end of 2007?

My original bites were large, very itchy, and have left lasting bumps and scars. I am now getting small bumps on my wrists and around my neck. Honestly, they aren’t as itchy, though they have lasted for over a week at this point and are more the size of small pimples rather than swollen. Maybe these are nymph bites? Or do nymph and adult bites not differ? In any case, I am of course paranoid now that the gentrol has just made things worse, with a generation of baby-boomers now infesting the cracks in my wall, the carpet, and my bed frame…

Only thing is, I still haven’t seen any since the spraying… Am I going crazy?

18 nobugsonme November 9, 2008 at 2:29 am


A lot of PCOs did not abandon Gentrol based on the information we referred to above, and I don’t think its use is going to necessarily hinder your treatment. We don’t have more information, I am afraid.

Based on the experiments of a few folks who have been bitten knowingly (under lab conditions), though I stress this is by no means a controlled study, there is no necessary and definite correlation between bite size and bed bug life stage. Bites can differ depending on the person, part of the person’a body, or time of day. Or, goodness knows, many other mysterious factors.

It is also apparent that some people’s bite reactions change over time (they may go from nothing to a reaction, and then back to almost nothing again over a period of time).

If you were treated twice, with the last visit two weeks ago, and apparent bites have just reappeared, I would assume you need more treatment. Please come to the forums if you want more support or suggestions:

19 proactive January 4, 2009 at 1:30 pm

Thank you very much for this information!

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