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Relative Susceptibility and Proximate Composition of Rice Varieties by
Sitophilus oryzae
L.
34
normal respiratory activity of the insects leading to
their asphyxiation and subsequent death (Yang et al.,
2006). This result did not acquiesced with the findings
of Anwar et al. (2005) in which jute bags treated with
neem oil was unable to achieve complete mortality of
R. dominica, T. castaneum, T. granarium
and
S.
granarius
at different concentrations. The ability of
the treated jute bag to prevent weight loss and damage
of the seeds after 42days of storage may be due to the
ability of the jute bags to retain the oil and its fume for
long period. The result obtained showed that the jute
bags treated at higher doses prevented the adult
emergence of the beetle and as well achieved
complete inhibition of the adults. The result obtained
on adult emergence could be as a result of high
mortality of the beetle which could therefore after
mating and egg laying capacity of the insect. This
agreed with work of Ashamo et al. (2013) in which oil
of
Newbouldia laevis
was found to prevent the
emergence of adult
Callosobruchus maculatus.
Also,
the ability of the bags to reduce or prevent the weight
loss and damage of seed stored in them may be due to
the ability of the oil used for their treatment to reduce
and prevent adult emergence of the beetle as
suggested by Idoko and Adeshina (2012). However,
result of this work revealed that jute bag treated with
E. aromatica
could not prevent weight loss and
damage of stored seed for long period as there was an
increase in the percentage of weight loss and damage
of seed stored inside them after six months. This could
be that the treated bags were only able to inhibit the
egg laid by the beetle from hatching for some period.
This also showed that the
E. aromatica
treated jute
bags only disrupted the normal life cycle of the insect.
This was in agreement with the work of Murdue-huntz
and Nibet (2000) as well as Yang
et al
.
(2006) which
suggested that botanical oils are found to disrupt
growth and reduced larva survival as well as
disruption of life cycle of insects. Moreover, jute bags
that were deep-soaked in the oil of
E. aromatica
showed a level of persistence in their effectiveness as
they were able to prevent weight loss and damage of
seeds stored in them for six months. The inability of
the botanical-treated jute bag to protect the weight loss
and damage of stored grains may be due to the fact
that botanical oils and powder lost their potency over
time as opined by Oruonye and Okrikata (2010). This
was in accordance with the result of Anwar
et al.
(2005) in which neem oil used for the treatment of jute
bags was found to reduced greatly in its effectiveness
as protectant against four stored product insect pest of
wheat. Also the result agreed with the work of Faditan
(2013) in which piper guineense oil treated jute bags
used for packaging maize grains was found to reduce
in its effectiveness over time. After six month of
storage, it was found that the wheat grains stored
inside treated jute bags have no colour change
regardless of the dose used and this may be due to the
fact the oil was not applied directly on the wheat
grains. This agreed with the findings of Anwar
et al.
(2005) in which neem oil treated jute bags have no
colour, flavour and taste effect on the stored wheat.
However, it was observed that there was a little
change in the odour of wheat grains stored inside
deep-soaked jute bags which in-turn affected its
acceptability. The treated jute bags however did not
affect the viability of the stored wheat after six months.
Regardless of the dose of the oil used for the treatment
of the bags, all the stored with achieved high rate of
viability. The use of
E. aromatica-
treated jute bags
may serve as an acceptable method of applying
botanical pesticides in protection of stored wheat for
more than 4-6months especially when the bags are
deep-soaked in the oil. Also, to increase the
effectiveness of these treated jute bags, the dose of the
oil used for their treatment could be increased as this
may have no toxic effect on the consumer (mammals)
since it is not in contact with the stored wheat. More
so,
E. aromatica
used for the treatment of the bags is a
medicinal plant and does not affect the viability of the
stored wheat.
Materials and Methods
Insect culture
The initial culture of
R. dominica
was obtained from
infested wheat grains from the Food Storage Research
Laboratory, Federal University of Technology, Akure.
The insects were subsequently reared in the laboratory
on cleaned wheat seeds at temperature of 28 ± 2°C
and relative humidity of 75 ± 5%. The wheat seeds
were kept inside plastic containers with the open end
covered with muslin cloth to prevent escape of insects
and to provide aeration.