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4. The effect of PBO on the House Dust Mite (Dermatophagoides pteronyssinus)
4.1. Introduction
Formulations of PBO 80% technical with 20% surfactant (PB80 EC) have been shown to be effective in controlling a number of mite species: Psoroptes cuniculi, which infests rabbit ears, were successfully controlled with a dose of 0.05% w/v; Psoroptes ovis, which infests sheep, were controlled with 100% kill at all doses over 1000ppm when applied in grapeseed oil; and Dermanyssus gallinae, which infests poultry, had an LD50 of 1755ppm in 24 hours. Below are details of two studies testing the effectiveness of PB80 EC against house dust mites (Dermatophagoides pteronyssinus).
4.2. Study 1
4.2.1. Materials and method
Three replicates of test solutions of PB80 EC were prepared in distilled water at 300ppm, 500ppm and 800ppm; distilled water also served as the control (three replicates). Standard cotton fabric was cut into 12 squares, 20mm x 20mm. Three cotton squares were soaked in each solution and the controls for 1 minute and then air dried for 24 hours. When dry each treated cotton square was fixed to a wire platform with non-solvent glue within an individual test chamber. After 24 hours to allow the adhesive to dry, twenty mites of mixed developmental stage were introduced into each test chamber which had been kept at 75% RH. Counts were made after 1, 4 and 24 hours of living, moribund and dead mites.
4.2.3. Results
All the test solutions yielded high mortality after 24 hours: 80.7%, 93.6% and 100.0% respectively for the 300, 500 and 800ppm treatments. The only recorded effect in the control was 5.3% mortality after 24 hours. The results are given in Table 4.1.
4.3. Study 2
4.3.1. Materials and method
Materials and method was the same as for Study 1 except three replicates of a test treatment of 100ppm PB80 EC was used and three replicates of the surfactant (Soitem 107) alone at 40ppm and 100ppm were tested to determine whether effects could be due to the action of the surfactant. The period of observation was extended from 24 to 48 hours.
4.3.2. Results
The results indicate that there was no increase in mortality from the PB80 EC at 100ppm over 48 hours when compared to the control. There was also no increase in mortality caused by the surfactant at 40ppm or 100ppm when compared to the control. The results are given in Table 4.2.
4.4. Conclusions
The surfactant (Soitem 107) had no detrimental effect on the mites when used at 40ppm and 100ppm when compared to the control. Therefore, it is assumed that the effects observed in Study 1 after 24 hours (at PB80 EC doses of 300, 500 and 800ppm) are due to PBO. At a dose of 100ppm the PB80 EC caused no significant mortality over a 48 hour period when compared to the control. go to top of page |
