International Journal of Horticulture, 2017, Vol.7, No. 9, 64-75
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different solvent recorded high mortality of
C. maculatus.
The general linear analysis done on the mortality
showed that there was significant interactive effect of the plant parts, the method of extraction and the
concentration of the extracts on the mortality of
C. maculatus.
It was noted in this study that the extracts of
A. occidentale
significantly reduced the oviposition and adult
emergence of
C. maculatus
and its ability to cause damage and weight loss of the protected cowpea seeds.
However, the oviposition and adult emergence of the beetle and its ability to cause damage and weight loss of the
cowpea changed with the parts of the plant used, method of extraction and concentration of the extracts. The
ability of the extracts to reduce oviposition of the insect could be due to inability of the insect to mate because
many of the insects must have been experiencing hyperactivity and convulsions as suggested by Isman (2006).
Botanicals have been reported to have ability cause sterility in insects (Isman, 2006; Zibaee, 2011). Therefore,
both the sexes of the beetle must have been sterilized because of their exposure to the extracts of
A. occidentale
and thereby reduced their oviposition rate. The regression analysis showed that mortality of the insect was
responsible more than 80% oviposition. So, low oviposition rate recorded could be due to high insect mortality.
However, the nut extracts of the plant recorded the lowest oviposition rate of the insect. The reduction or
prevention of the adult emergence of
C. maculatus
recorded in the study might be due to inability of the insect to
lay many eggs. Isman (2006) reported that botanicals have ability of inhibiting the synthesis and release of
ecdysteroids from their prothoracic gland and this in turn causes incomplete ecdysis in their larvae. Therefore, the
prevent or reduction in adult emergence of
C. maculatus
by the extracts of
A. occidentale
could be due to inability
of the insect larvae to castoff their exoskelecton which remained connected to their posterior abdomen. Digestion
of food is playing an important role in the existence of living organisms and it involves assistance of many
enzymes. The disruption of the normal activities of these digestive enzyme causes inability of insects and other
living organisms to provide their nutrients for biological requirements (Zibaee, 2011). Botanical insecticides have
been noted for the inhibitory effect on wide range of digestive enzymes in insect (Zibaee and Bandani, 2010).
Several botanical extracts have been reported of inhibiting the a-amylase, glycosidases, lipases and proteases
(Terra and Ferriera, 2005; Senthil et al., 2006; Shekari et al., 2008; Zibaee et al., 2008; Zibaee et al., 2009).
Therefore, no or low percentage adult emergence of
C. maculatus
exposed to different extracts of different parts of
A. occidentale
could be due to inability of the insect larvae to digest the treated cowpea seeds which in turn lead to
their death. The result of this work acquiesced with the findings of Epidi and Udo (2009) in which different
extracts of
Ricinodendron heudelotii
reduced the emergence of
C. maculatus
. Also, the findings of Abd-Elhady
(2012) concise with the results of this study as the essential oil of
Artemisia Judaica
was found to significantly
affected the life stages of
C. maculatus.
The prevention or reduction of the damage and weight loss of the protected cowpea seed achieved by the extracts
of
A. occidentale
may due to inability of the insect larvae to fed on the protected cowpea seeds as suggested by
Ogungbite (2015). The linear regression analysis showed that more than 98% of the seed weight loss was
determined by the adult emergence. Consequently, no or low weight loss recorded by the seeds reflected no or low
adult emergence of the beetle.
4 Conclusion
The results of this research have proven biocidal efficacy of extracts of different parts of
A. occidentale
against
C.
maculatus
and its ability to cause damage and weight loss of cowpea seeds. The result showed that only little
concentrations of the extracts were required to achieve high mortality of the insect. Also, it was revealed that the
mortality of the insect had significant effect on oviposition and weight loss of the seeds respectively as reflected
by the linear regression analysis. However, the nut extracts of the plant showed more biotoxic efficacy against the
insects than other parts of the plant while the ethanolic extracts of the plants recorded the highest biocidal efficacy
on the insect. Since, the extracts of
A. occidentale
have proven insecticidal against
C. maculatus
it could be
introduce to management system of the insect. Moreover, the ethanolic extracts of the plant appeared more
promising than other extracts while the nut of the plant showed more biocidal efficacy.
