Wednesday, January 31, 2007

Managing insecticide resistance

As I said from the very beginning, the sole purpose of this Blog is to share some of my knowledge and experience with others. Many people chose to move on and leave the horrific experience behind once they removed their infestations, which is understandable. I decided to write something down since I believed that it could be invaluable to others. And because I am a sufferer myself and there is no personal interest involved, it is much easier for me to keep my views unbiased.

Also I would like to make it clear that many of the theories, particularly the recent ones on insecticide resistance, are not based on my personal assumptions, but rather are well established theories with solid technical foundation. I only explained it in my own words to make them easier to understand. Although I am not a pest control expert or entomologist, my background in applied science and first hand experience do help me understand these theories. To make sure not to mislead the readers, I won't make any conclusions without doing adequate research or experiments.

Besides the strategies covered last time, there are a few more practical ones to prevent or delay insecticide resistance.

1. Saturation.

This is to overwhelm the insect population's resistance with heavy dose of an insecticide. As I mentioned before, resistance is a comparative term. By increasing the dosage, even resistant individuals could be killed. The aim is to eliminate the RS individuals since the RR individuals may not be killed even at very high dosage (see my previous post for the labeling of RR, RS and SS). After the insecticide is applied, susceptible individuals may be introduced to mate with the survivors to reduce the frequency of the R alleles. It is generally not practical to use this strategy in a residence since it could cause significant damage to the health of the residents and the environment. (Revised on Feb 23, 2007) But extra dosage can be applied to limited areas, especially where harborages have been found. And intentionally or not, some PCOs do use this strategy. The concept can be borrowed when using non-toxic insecticides such as DE by increasing the dosage, or when using alternative control measures such as cold and heat treatment by extending the time period or by increasing the temperature settings. When applying these control measures, it is important to make sure that all bedbugs are killed, since the survivors are always the most adaptive ones.

The strategy works the best when the targeted area can be isolated and the insecticide leaves no residue. For example, Vikane gas fumigation is being used to treat bedbug infestation and is becoming more and more popular. Since a structure is completely sealed (tented) before fumigation, and Dow AgroScience claims that Vikane leaves no residue, it is possible to increase the dosage rate without causing significant side effects. Currently three times the dosage rate of Vikane used for drywood termites is prescribed for bedbug fumigation. With enough concentration and sufficient penetration time, even eggs can be killed. Vikane chamber can also be used to treat furniture and possibly vehicles. The technique sounds promising and does not cause significant damage to human health or environment. However, the cost of Vikane gas fumigation is significantly higher, and it is impossible to treat a multi-family dwelling without the co-operation of every unit. The long-term effects of using Vikane gas are also not clear.

2. Rotation & Tank mixing

Rotation is a strategy commonly used by some PCOs. Basically, you rotate insecticides with different mode of action. If 0.01% individuals of a bedbug population are resistant to each one of two insecticides, then only 0.000001%, or one in every one hundred millions are resistant to both. So in the example from my previous post, if we applied two insecticides in rotation, then the 100 bedbugs survived the first insecticide would have been eliminated by the second insecticide. Also, resistance is usually not very stable at the early stage of its development, and might revert to susceptibility once the insecticide isn't used. Therefore Rotation may delay the development of resistance.

Tank mixing works in the similar way. But instead of applying different insecticides in rotation, you use them at the same time. For instance, pyrethroid and carbamate "two-in-one" treated bed nets have been used in Africa for malaria vector control to improve the effectiveness of the bed nets. (Updated on Mar 2, 2007. Strictly speaking, treating bed nets with both pyrethroid and carbamate may not be considered as tank-mixing, since pyrethroid and carbamate are applied to different parts of bed nets. Tank-mixing, as the name implies, typically mixes two or more pesticides, and could have some undesirable problems such as incompatibility between pesticides, or reduced overall effectiveness if one pesticide is repellent to the target pest.)

This strategy works only when the insects haven't developed resistance to either insecticide. If resistance to one insecticide is already evident, then basically we would be using only one insecticide, and the insects will eventually be resistant to both insecticides.

Currently, the biggest problem with this approach is that we, including the PCOs, have very limited choices. Many insecticides, especially those broad-spectrum contact and stomach poisons have been banned or restricted in the past due to health and environmental concerns as well as political reasons. Development of new insecticides is also slow and costly due to both technical and bureaucratic reasons. The development of many insecticides in the past has either failed or been rejected due to cross-resistance. The cost of having a product registered is now estimated to be around $100 million, according to Dr. Dini Miller. To make things worse, according to the Federal Insecticide, Fungicide, and Rodenticide Act, all pesticides registered before Nov 1, 1984 are required to be re-examined. Manufactures not only have to pay a re-registration fee, but also need to prove that the pesticide would not endanger human health and environment. Many manufactures simply chose to stop making the pesticide to avoid the heavy cost involved.

3. Integrated Pest Management

The basic rule is to use alternative control measures wherever possible, and use chemical as a last resort. This is not to say that we should abandon chemicals altogether, but rather should use them wisely and more effectively. IPM was practiced well before the arrival of synthetic chemicals, even though the term was formalized in 1969 by US National Academy of Sciences. But since organosynthetic insecticides were so effective when first introduced, all other control measures were virtually abandoned. However, within a decade of its introduction, organosynthetic insecticides started to lead to disastrous consequences such as widespread insecticide resistance, secondary pest development, elimination of natural enemies, environmental hazards, and so on. Since then, the focus has been gradually shifted back towards Integrated Pest Management. Many "soft insecticides" were developed in the 70's and the 80's to target specific pests and to reduce environmental hazard, lots of efforts have also been put into biological control since the 90's. Insecticides are now applied only to the infested area and only when necessary. Today, pest control is no longer as simple as hiring a PCO to spray some chemical. For instance, education and participation of the customer (ourselves) are playing a more and more important role. We all know that preparation is the key to the success of a bedbug treatment. In fact, many PCOs won't even accept the job if the preparation work isn't properly done.

However, since chemical always seems to be a quick solution, when it comes to pest control, most people will only think of chemical. According to a survey (available in Nov 2006 issue of Pest Control Technology) done by our Yahoo Bedbugger Member, Ms. Jody Gangloff-Kaufmann and her colleagues, most PCOs didn't recommend the use of alternative control measures other than throwing away things and vacuuming. This is worrisome since I believe that relying heavily on chemical is one of the main reasons why so many treatments have failed. But PCOs are not the only ones to blame, it's really our own responsibility to do thorough pre- and post- treatment work to help ensure the success of treatment.

Finally I want to cover one more strategy that I've mentioned before, which is to use ourselves as the bait to lure the bedbugs to cross the insecticide and get killed. This is not an official strategy but seems to be gaining popularity. However, as Richard Cooper of Cooper Pest Solutions pointed out in his article "Bed Bugs - Still more questions than answers: a need for research and public awareness" (available in summer 2006 issue of American Entomologist), after an insecticide is applied, bedbugs would typically leave the treated area for four to five weeks, and then come back only if the same insecticide isn't applied again. Insects have much better senses than human beings do, if we don't like chemicals, can we really be so sure that bedbugs will not try to avoid them? In addition, if the bedbug population happens to be resistant to the insecticide applied, this strategy could backfire, especially if you are advised to not protect your bed. I am not opposing the use of this strategy, and I do respect the logical thinking behind this practice, but extreme caution should be taken. As always, it is dangerous to rely heavily on one single control measure, let alone one single strategy. (Revised on Mar 05, 2007. A recent research from Virginia Tech found that none of the insecticides tested including the pyrethroids was repellent to some laboratory strain bedbugs. But since many earlier researches and field observations indicated otherwise, I think it is too early to make the conclusion that pyrethroids aren't repellent to bedbugs.)

Although our choice is very limited, we still have a few insecticides to use. By properly using these insecticides and by combining insecticide treatment with alternative control measures, I believe we still have very good chance to keep bedbugs out of our homes. The strategies covered above can be practically employed in our battle against bedbugs. For example, if the bedbugs are resistant to pyrethroids, then we can try Phantom (Chlorfenapyr), Sterifab (alcohol based), refined petroleum oils, rubbing alcohol ,insecticidal soaps, and so on. By the way, quite a few people from Yahoo Bedbugger Group had success with Murphy's oil soap. Diatomaceous Earth can be dusted along the baseboard so that the bedbugs can't reach you without being detected. If the bedbugs try to live longer by hiding in the cracks and maintaining slow metabolic rate, then we can drive them out with a repellent. Even if they don't get killed by the chemical, don't get detected and killed by us and don't hit the DE on the floor, they will at least consume lots of energy. All we have to do then is to protect ourselves so that they won't get the badly needed food. Can they still live more than one year now? I don't think so. Without sufficient nutrition, they will only be more susceptible to insecticides. If the bedbugs become resistant to insect growth regulator, then we should stop feeding them by protecting ourselves. Remember they need our blood to reproduce? If the bedbugs feel they can escape insecticides by hiding deeply in the cracks, then we can simply caulk the entrance and keep them in there permanently. And if the bedbugs are in the vacuum bag, then we can rinse it with boiling water before throwing it out, the temperature of boiling water is 100 degrees Celsius, twice as much as the temperature required to kill all stages of bedbugs (thermal death point), and is lethal enough to kill instantly on contact!

As you can see, we do have quite a few weapons, why don't we use them all? If a bedbug is resistant to one insecticide, then it will be killed by another insecticide or other measures. By combining all weapons available, we will greatly improve our winning chance. Once we stop focusing exclusively on chemicals and start thinking outside the box, we will see things differently, and there will be options and solutions. By taking an integrated approach, we will have much better chance of defeating our enemy.


Anonymous PestControlConnoisseur said...

These are some really great ways to eliminate bed bugs. I haven't heard much on IPM, but you explained it really well. Thanks for the information!

2:58 PM  
Anonymous Anonymous said...

No mention of high heat (Steam)?

12:40 PM  
Blogger Frank said...

Anonymous said...
No mention of high heat (Steam)?

I will have a separate post on heat & cold treatment. Thanks for reminding me.


2:27 PM  
Blogger Allvira said...

Thanks for the helpful post for pesticides control. Yup you have dictates it here in very well formed words.Insecticide resistance must be followed in this manner. Wonderful post.

1:17 AM  
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10:44 PM  

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