Page 32 - Volume 6, Issue 1, January 2013

© Benaki Phytopathological Institute
Theou et al. 30
ing to genus Tribolium are known to secrete
carcinogenic chemicals known as quinones
when they occur in large numbers (Hodges
et al., 1996).
Although the fumigant action of many
essential oil vapours against T. castaneum
has been studied thoroughly (Kim et al.,
2010; Liu and Ho, 1999; Mediouni et al ., 2012;
Mohamed and Abdelgaleil, 2008; Mondal
and Khalequzzaman, 2010; Rice and Coats,
1994; Safavi and Mobki, 2012), very little
relevant information is available on T. con-
fusum (Haouas, 2012; Işikber et al., 2006;
Işikber et al ., 2009), a very common spe-
cies in Northern Greece and well adapted
at the cold-dry environments of most store-
houses (Stamopoulos et al., 2007). The two
aforementioned species are known to differ
in many aspects of their response and sus-
ceptibility to xenobiotic compounds (Amos
et al ., 1974; Arthur, 2003). Moreover, essen-
tial oils while are generally active against a
broad spectrum of stored product pests, in-
terspecific toxicity of individual oils is highly
idiosyncratic (Isman, 2000).
The present study was undertaken to in-
vestigate the toxicity of Lavandula hybrida
Rev. (Lamiaceae), Laurus nobilis L. (Lauraceae),
Thuja orientalis L. (Cypressaceae), Citrus sinen-
sis Osbeck. (Rutaceae), Citrus limon Osbeck.
(Rutaceae) and Origanum vulgare L. (Lamiace-
ae) essential oil vapours on T. confusum larvae,
pupae and adults. The relation between the
age, stage and sex of the insect and its vulner-
ability to these vapours were also studied.
Materials and methods
Biological material
Tribolium confusum larvae, pupae and
adults were obtained from laboratory cul-
tures maintained in large glass jars (30 cm
height, 8 cm diameter) with wheat flour at
26 ± 1 °C, 65 ± 5% r.h. and a photoperiod of
12 h light, 12 h dark.
Isolation of essential oils
Essential oils were obtained by subject-
ing plant materials to hydrodistillation using
a Clevenger apparatus (Winzer®), from the
following plant parts: L. hybrida (whole flow-
ering plants), L. nobilis (fruits and leaves), T.
orientalis (fruits), C. sinensis (peels from ma-
ture fruits), C. limon (peels from mature
fruits), O. vulgare (whole flowering plants).
The plants were collected in mid July from
the region of Thessaloniki (Northern Greece)
except for the fruits of C. sinensis and C.
limon , which were collected in December
from the area of Arta (Western Greece). The
distilled essential oils were dried over anhy-
drous sodium sulphate and stored in a freez-
er at -10ºC until use.
Bioassays
In order to test the toxicity of essential oil
vapours to the immature stages and adults
of T. confusum, gastight glass jars of 370 ml
volume with metal screw-caps were used as
exposure chambers. A small piece (3 x 3 cm)
of Whatman No 1 filter paper was attached
to the undersurface of the cap to serve as an
oil diffuser after the appropriate amount of
pure essential oil had been applied. Doses
were calculated based on nominal concen-
trations and assumed 100% volatilisation of
the oils in the exposure vessels.
In each jar, 20 insects were placed at the
appropriate stage of development i.e. 10-,
25- and 31-days-old larvae, 2-days-old pupae
(males and females were exposed separate-
ly) and 10- and 60-days-old adults (males and
females were exposed separately) were used.
Males and females were separated as pu-
pae based on morphological characteristics
of genital papillae and kept separately until
their use. In females, the genital papillae are
pointy, with 2 darker dots on the tip of each,
and roughly half the size of the urogomphi
whereas those of males are stubby, conjoined
and barely noticeable (Park, 1934).
After 48h of exposure to essential oil va-
pours, the insects were transferred to plastic
Petri dishes containing wheat flour. All dead
insects were counted by the fourth day, ex-
cept pupae which were kept for a further
4 days, with those that failed to complete
morphogenesis and/or produced develop-
mental intermediates or ‘adultoids’ (pupal-