Abstract
Essential oils of
Ocimum basilicum
(L.),
Achillea fragrantissima
(Forssk.) and
Achillea santolina
(L.) were obtained by hydrodistillation and analyzed using gas chromatography (GC) and GC/mass spectrometry (MS). Oil-in-water nanoemulsions (10% active ingredient) were prepared through a high-energy (ultrasonication) emulsification process. Nanoemulsions were characterized by viscosity, pH, thermodynamic stability, droplet size, polydispersity index (PDI) and scanning electron microscopy (SEM) measurements. The plant oils and their nanoemulsions showed considerable acaricidal activity against the mold mite,
Tyrophagus putrescentiae
(Schrank) (Sarcoptiformes: Acaridae). In a contact toxicity bioassay and 48 h post treatment,
O. basilicum
oil was the most toxic, followed by
A. fragrantissima
and
A. santolina
, where LC
50
values were 8.4, 14.1 and 21.8 µl/cm
2
, respectively. LC
50
for benzyl benzoate, a standard acaricide was 9.8 µl/cm
2
. Upon fumigation, responses also varied according to the test oil. Based on the 48-h LC
50
values, the same manner of activity was also observed, where
O. basilicum
was the most toxic followed by
A. fragrantissima
and
A. santolina
. When prepared as nanoemulsions (particle size from 78.5 to 104.6) and tested as fumigants, toxicity of the oils was increased drastically with LC
50
values of 2.2, 4.7, and 9.6 µl/l air for
O. basilicum
,
A. fragrantissima
and
A. santolina
, respectively. The oils showed a moderate to strong residual acaricidal activity, where
O. basilicum
oil was the most effective. The results suggest that appropriate nanoemulsions containing the tested oils can be developed to control
T. putrescentiae
after the required toxicological assessments.