Q&A with Graham Moores: A deep dive into Piperonyl Butoxide (PBO)

1) What is Piperonyl Butoxide and why is it so important in the pest control industry?

PBO is a pesticide synergist; it enhances the activity of pesticides whilst having little or no insecticidal activity itself. Originally used in the United States to ‘stretch’ limited supplies of natural pyrethrum, but it can be used alongside many insecticides to enhance their activity.

2) How does PBO function as a synergist in pesticide formulations?

It acts primarily by inhibiting the metabolic enzymes that would otherwise break down the insecticides. Insects have a natural defence system consisting of P450 and esterase enzymes that are able to metabolise natural toxins that they may encounter. For example, specific insect species can feed upon tobacco or cotton, plants that contain amounts of nicotine or gossypol respectively. They are only able to do this because they have specialized P450 or/and esterases that will detoxify these chemicals.

When they come into contact with insecticides; these same enzyme systems may be able to metabolise the insecticide. Piperonyl butoxide inhibits these enzyme systems, so the insect is defenceless against the toxin.

Furthermore, in many cases PBO also helps the insecticide cross the cuticular barrier of the insect, aiding absorption.

3) In what types of pest control products is PBO most commonly used?

I think PBO is best known for its inclusion in household sprays and aerosols; pick up a fly spray and it will inevitably contain PBO alongside an insecticide, usually a pyrethroid. However, PBO is also present in many mosquito bed nets, countering insecticide-resistance in mosquito populations; it is present in some medical personal hygiene products for control of lice; flea and tick treatments for pets; it is also used to help against stored product pests, grain storage and also in agriculture.

4) How does the presence of PBO affect the efficacy and longevity of pyrethroid-based insecticides?

Well, as I said previously, PBO inhibits the metabolic enzymes in insects that would otherwise breakdown the insecticide, including pyrethroids. This results in greater efficacy as the insect, even a resistant insect, will become susceptible or even hypersensitive to insecticides once its defence enzymes are inhibited. It also means the insecticide will last longer in the body of the insect, improving longevity. It also means that on something like a bed net which has to provide protection for months or even years, if the insecticide is slowly disappearing in the environment, the presence of PBO would still enhance the residual effects of the remaining insecticide.

5) What role does PBO play in integrated pest management strategies?

To my mind, IPM does not mean ‘no insecticides’ but rather an integrated approach that reduces a reliance on insecticides, or reduces insecticidal rates. As a synergist, PBO fits perfectly within an IPM strategy as PBO-enhanced formulations provide greater efficacy and longer lasting-control. It allows the opportunity to lower insecticide rates and thus lower environmental impact.

6) Are there concerns about resistance development in pests due to widespread PBO use?

I am sure there are concerns, but we have to be careful about what is meant by resistance to PBO. Piperonyl butoxide has been around for a long time, and there are only a few documented cases of true resistance to PBO; in all these cases, the resistant population was so unfit that they died out within 1 or 2 generations.

Perhaps of more concern is resistance to the effect of PBO. That is, using a synergist to suppress resistance would only increase resistance to even higher levels. But, trials have shown that this does not happen, and conversely the use of a synergist (PBO) in fact slowed the development of resistance.

7) How do you address concerns from consumers or advocacy groups about its safety?

I know that PBO has been extensively evaluated by such bodies as the EPA and BPR for any mammalian toxicity concerns, and, as far as I am aware, no concerns have been forthcoming. The bottom line is that PBO is capable of reducing the insecticidal load that it is applied with, and that insecticidal load is always going to be more toxic that the PBO itself.