Page 47 - Volume 2,Issue 2, July 2009
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© Benaki Phytopathological Institute
Sublethal effects of essential oils on
Acanthoscelides obtectus
93
Data concerning the adult weight, adult
longevity, fecundity, egg hatchability and
pupae developmental time, were analysed
by using one way analysis of variance (ANO-
VA) followed by the least significant differ-
ence test (LSD) for means separation (24, 25).
Means of the larvae developmental timewere
compared with the Mann-Whitney U test, as
the obtained data did not satisfy the assump-
tions required for a parametric test (24).
Results
Delayed mortality
The recorded mortality four days after
the exposure of larvae or pupae to essential
oil vapours did not differ significantly from
that recorded after the emergence of adults
for all essential oils and doses tested (t test,
all P>0.05) (Figure 1) indicating that the ma-
jority of larvae and pupae were killed during
or immediately after the treatment phase.
Sublethal effects
Lavender essential oil
Exposure of larvae to lavender essential
oil vapours did not significantly affect the de-
velopmental time from larvae to adult emer-
gence at all doses tested except for that of 2
μl/l air (Mann-Whitney U test, Table 1). Weight
and longevity of adults were also not signif-
icantly affected (males: F
3, 83
= 1.727; F
3, 131
=
0.730; females: F
3, 100
= 2.502; F
3, 115
= 2.618; all
P > 0.05, for weight and longevity, respective-
ly). Females derived from larvae exposed to
the highest dose of lavender essential oil va-
pours deposited fewer eggs than control fe-
males (F
3, 49
= 3.982, P < 0.01), but egg hatcha-
bility was not affected (F
3, 45
= 2.807, P > 0.05).
Exposure of pupae to lavender essential
oil vapours resulted in extension of the devel-
opmental time from pupae to adult for both
sexes, only at the highest concentration test-
ed (males: F
3, 128
= 4.916, P < 0.01; females: F
3, 134
= 5.898, P < 0.001) (Table 2). The adult weight
and the longevity of male survivors were not
affected (weight of males: F
3,53
= 1.001, P>0.05;
weight of females: F
3, 51
= 0.629, P > 0.05 and
longevity of males: F
3, 84
= 0.805, P > 0.05). The
longevity of the female survivors in all dos-
es tested was significantly lower compared
to control (F
3, 65
= 11.631, P < 0.001), whereas
females laid fewer eggs (32-42%) at the two
higher doses (F
3, 34
= 3.721, P<0.05). The hatch-
ability of the eggs laid was not significantly
affected (F
3, 32
= 0.662, P > 0.05).
Rosemary essential oil
After exposure of larvae to rosemary es-
sential oil vapours, the developmental time
of larvae was significantly affected only at the
highest dose tested (Mann-Whitney U test,
Table 3). Exposure to the highest dose also
caused a reduction in adult male weight (F
3,
78
= 5.841, P < 0.001), whereas the weight of
females was not significantly affected (F
3, 89
= 1.469; P>0.05). The longevity of the adults
of both sexes was not significantly affected
(males: F
3, 107
= 0.370; females: F
3, 98
= 1.300, all
P > 0.05). Females derived from treated larvae
laid approximately 23-35% fewer eggs at all
doses tested (F
3, 49
= 4.486, P < 0.01) compared
to control, but egg hatchability was not sig-
nificantly affected (F
3, 49
= 0.496, P > 0.05).
After exposure of pupae to rosemary es-
sential oil vapours, the developmental time
from pupae to adult was significantly affect-
ed only for the male survivors at the highest
dose tested (males: F
3, 163
= 4.073, P < 0.01; fe-
males: F
3, 147
= 2.036, P > 0.05) (Table 4). The
weight of the adult survivors did not differ
from that of the control insects except for
the female survivors derived from the high-
est dose tested (males: F
3, 53
= 1.73, P > 0.05;
females: F
3, 59
= 4.322, P < 0.01). No nega-
tive effects on the longevity of male survi-
vors was recorded (F
3, 125
= 2.289, P > 0.05),
while the longevity of the adult females was
reduced at all doses tested (F
3, 89
= 12.036, P
< 0.001). Moreover, the female survivors laid
fewer eggs at the two higher doses (F
3, 36
=
4.253, P < 0.01), but egg hatchability was not
significantly affected (F
3, 33
= 0.201; P > 0.05).
Eucalyptus essential oil
Exposure of larvae to eucalyptus essen-
tial oil vapours prolonged the developmen-
tal time from larvae to adult for both sexes at
