Tetranychus urticae
Koch (Acari: Tetranychidae) is an
economically important pest of agricultural and ornamental
crops worldwide. It has been shown that many of natural
plant-based pesticides have fewer side effects compared
with synthetic chemicals. The essential oils of plants have
been broadly studied for pest-control, including toxic
and repellent effects, antifeedant, ovicidal, and other
properties. Essential oils from stems, flowers, and leaves of
Piper marginatum
Jacq. were evaluated in the laboratory
regarding their acaricidal potential against the two-spotted
spider mite (
T. urticae) and the results were compared with
eugenol as a positive control. The oils were also evaluated
with regard to the susceptibility of the natural enemy of
T. urticae (
Neoseiulus californicus
McGregor). Based on
LC
50 estimates, oils from stems and flowers exhibited the
same toxicity and differed significantly from the leaf oil
with LC
50 0.37, 0.56, and 3.77 μL L
-1, respectively. None
of the oils tested exhibited toxicity greater than or equal
to that of the positive control. The oil mortality rate was
significantly lower for
N. californicus (50% to 70%) than
for
T. urticae (> 95%). The
P. marginatum oils also deterred
oviposition. Among the chemical constituents tested,
sesquiterpenes were more toxic with an LC
50 of 2.89 μL
L
-1 than phenylpropanoids
Z-asarone and
E-asarone with
LC
50 6.64 and 8.51 μL L
-1, respectively. The acaricidal
properties, oviposition deterrence and selectivity make
these oils strong candidates for use as the active ingredient
in a plant-based acaricidal agent.