The repellent efficacy of 17 essential oils against the German cockroach, Blattella germanica was examined
using a T-tube olfactometer. Five oils repelled B. germanica with good efficacy, ranging from 70.0 to 96.7%.
Four of these oils, grapefruit, lemon, lime, and orange, were from the citrus family Rutaceae. These citrus essential
oils showed similar repellent activity against two more cockroach species, such as Periplaneta americana and
P. fuliginosa. Gas chromatography (GC) and GC-mass spectrometry analyses revealed that the major components
responsible for the repellent activity of the citrus oils were limonene, b -pinene and g -terpinene. Limonene appears
to be the main component responsible for the repellent activity rather than b -pinene and g -terpinene. The
repellent efficacy of these components varied with different doses and the cockroach species tested. It is likely
that minor components of the oils also contributed to the overall repellent activity of citrus essential oils, except
orange oil. The activity of orange oil is almost solely attributed to the activity of limonene. Also, the repellent activity
of citrus oil and that of each of the terpenoids makes little difference to the efficacy of a repellant against
the three species of cockroaches. © Pesticide Science Society of Japan