Abstract
Essential oils of
Achillea biebersteinii
,
Achillea santolina
and
Achillea mellifolium
were obtained by hydrodistillation and analyzed using gas chromatography/mass spectrometry. The plant oils were tested for their toxic and repellent activities against the Khapra beetle,
Trogoderma granarium
(Everts) (Coleoptera: Dermestidae).
T. granarium
was sensitive to the oils via topical application, contact and fumigation bioassays, where
A. biebersteinii
oil was the most toxic regardless of the technique used. Using topical application, a dosage of 15 μg/mg insect of
A. biebersteinii
oil was sufficient to kill 100 and 83.2.0 % after 7 days exposure of adults and 2nd instar larvae, respectively. Meanwhile, twice this concentration of
A. santolina
and
A. mellifolium
oils caused 90.4 (72.5 %) and 73.8 (60.1 %) adult and larval mortality after 7 days, respectively. Using fumigation and 7 days exposure, a concentration of 50.0 μl/l air of
A.
biebersteinii
oil displayed the strongest activity (percentage adult and larval mortalities of 100.0 and 88.0 %), respectively, while
A. santolina
and
A. mellifolium
oils at the same concentration caused 92.5 (76.8 %) and 76.1 (61.3 %) adult and larval mortality, respectively. The three oils were strongly repellent to the larvae and adults of
T. granarium
. The repellent activity was time and concentration-dependent, where
A. biebersteinii
oil was the most effective, even though at low concentrations (percentage repellency of 100 and 81.0 % were recorded against adults and larvae after 6 h exposure to a concentration of 0.22 μl/cm
2
, respectively). Results suggested the potential use of
Achillea
oils as natural grain protectants against
T. granarium
.