Piperonyl Butoxide (PBO) pages

1. PBO - Introduction
2. PBO - Household
3. PBO - Resistance
4. PBO - Dust Mite
5. PBO - Herbicides

2. PBO in Household and Industrial Insecticide Sprays

The main advantages of including PBO in insecticide formulations are:
1. Increased rate of ‘knock down’ particularly in the first few minutes after spraying;
2. A dramatic improvement in final mortality (kill) with no recovery after knock down;
3. Improved cost-effectiveness benefiting both the manufacturer and the user;
4. Improved action against insects which have developed resistance to pyrethroid insecticides;
5. Greater ease of formulation.

2.1. Increased rate of ‘knock down’
Both Tetramethrin and Pyrethrins are widely used in insecticidal sprays in order to achieve a rapid knock down (KD) effect on insects. The results shown in Tables 1 and 2 clearly indicate that the addition of PBO to insecticides increased the rate of KD to houseflies. This is important because most market research has shown that the most desirable property in a household spray is rapid KD.

The optimum ratio of PBO to insecticide is best determined by experiment and an assessment of relative costs so that both biological and economic data are considered. The optimum ratio varies with the target species but in practice, control of houseflies is usually generally applicable. The data in Table 2.1. were obtained from testing the effect of progressively increasing the amount of PBO in a formulation containing a constant amount of Tetramethrin. The tests, under uniform conditions, comprised four replicates of 200 flies each.

The results indicate that the addition of PBO significantly enhances the efficacy of the formulation both by improving KD and mortality in 24 hours. In addition, the results indicate that, as the amount of PBO is increased, the effect of each added amount decreases. In fact, other studies show that the synergist to dose response is logarithmic. Thus the optimum ratio is between 1:4 and 1:8 and given the costs of tetramethrin and PBO, it can be seen that the overall optimum ratio is about 1 part insecticide to 5 parts PBO.

It has been suggested that when tetramethrin or pyrethrins are included in a formulation solely for their KD properties and another pyrethroid is added to effect kill, such as d-phenothrin, then there is no need to add any PBO. This is not correct as it ignores the pronounced synergism for KD as the data in Table 2.2. and Table 2.3. indicate. In addition, in the biological testing of two branded insecticide aerosol space sprays against houseflies the dramatic effect of PBO on early KD and kill can be seen; the synergised product, without an additional killing agent, is clearly superior. In the study both samples contained 0.35% tetramethrin, Sample A contained, in addition, PBO and sample B, bio-resmethrin; the results are shown in Table 2.4.

2.2. A dramatic improvement in final mortality (kill) with no recovery after knock down
The expectation of the user of a household insecticide is that KD will be rapid and all paralysed insects will die. This expectation can be successfully met with the correct formulation of PBO. The data in Table 2.5. clearly indicate that a significant percentage of houseflies paralysed by a concentration of tetramethrin as high as 0.5% recover from KD without the addition of PBO.

2.3. Improved cost-effectiveness benefiting both the manufacturer and the user
The formulations used in Tables 1–5 were designed to yield mortality well below 100% so that valid comparisons could be made between the test concentrations and ratios. In practice, higher percentages of tetramethrin are required to produce effective products containing from 0.25% to 0.40% Tetramethrin synergised with PBO at a 1:5 ratio. In oil-based formulations concentrations of PBO above 2.0% may irritate a small percentage of users; this is not a problem in water-based formulations.

2.3.1. The effect of adding PBO to tetramethrin to control cockroaches
In a study of the effect of different ratios of tetramethrin and PBO against the German cockroach (Blattella germanica) Chadwick (1971) found that the rate of KD was barely affected by the addition of PBO at 1:5 but the effect on kill was significant (see Table 2.6.).

2.3.2 The effect of adding PBO to tetramethrin to control mosquitoes
Mount et al (1974) in a study of mosquitoes (Aedes taeniorhynchus) calculated factors of synergism which they defined as the LD90 of Tetramethrin alone divided by the LC90 of tetramethrin plus PBO. These factors are summarised in Table 2.7.

2.3.3 The effect of adding PBO to various pyrethroids to control insects attacking grain
Lloyd (1973) and Bengston et al (1983) demonstrated that a wide range of pyrethroids including Deltamethrin and Phenothrin as well as first generation pyrethroids such as tetramethrin were all effectively synergised by PBO when tested against grain weevils, flour beetles and other pests attacking grain.

These results clearly indicate that the newer and more active pyrethroids such as Deltamethrin respond in an economical manner to synergism by PBO contrary to earlier suggestions.

2.4. Improved action against insects which have developed resistance to pyrethroid insecticides
This has been reviewed by Glynne Jones (1983). There is good reason to believe that the addition of PBO to all pyrethroid formulations used in the home and for public health purposes will assist in delaying the onset of resistance.

In the USA PBO has been used successfully with Permethrin and Fenvalerate against Colorado Beetle which previously had developed resistance to both insecticides. PBO has also been used successfully with Rotenone and trials are being undertaken of PBO mixed with various new Insect Growth Regulators. See section 3. for more detailed information on resistance.

2.5. Greater ease of formulation
The good solvent properties of PBO have been shown to assist in the formulation of active ingredients such as Tetramethrin, Pyrethrum and Deltamethrin that have a low oil solubility. In addition, since PBO absorbs strongly in the UV region of the spectrum it can assist in retarding the degradation of insecticide active ingredients. It has also been found that PBO appears to stabilise formulations.

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