We developed a novel laboratory method (Fig. 1) for the evaluation
of the repellent potential of Citrus oils to impede the
migration of T. urticae between plants via strings in a greenhouse. In
the first experiment, the strings were immersed in a 1% MeOH
solution of the essential oils or pure compounds and the miteswere
released immediately onto a plastic disc. Numbers of mites found
on the initial disc and the disc joined by the string were made after
one, two and three hours. In the second experiment, strings were
immersed in the solutions 24 h prior to the release of the mites and
the evaluation was performed after one, two and three hours to
determine the residual repellent effect of the solutions. The test
arena consisted of a plastic Petri dish (20 cm in diameter). Mites
were placed in a smaller plastic Petri dish (3.5 cm diameter) lined
with a green plastic disc (2.5 cm in diameter). This Petri dish was
connected to two bean leaf discs (2.5 cm in diameter) by string
(4.0 cm in length) on each side, which served as bridges for the
mites to cross from the middle plastic disc to the bean leaf discs on
either side of the central Petri dish. One end of the string (1.0 cm)
was placed in the slits of the middle Petri dish and the other
(1.0 cm) was placed on the bean leaf disc. Filter paper disks (3.5 cm
in diameter) saturated with water were placed under the leaf discs
to keep the leaf discs from wilting and to prevent escape of the
mites.