International Journal of Horticulture, 2017, Vol.7, No. 9, 64-75
71
Table 5 Correlation between insect adult emergence and weight loss of C. maculatus exposed to A. occidentale extract
Plant parts Extraction
methods
R
R
2
Ad (R
2
) K ±S.E
R
c
±S.E
R
E
t-value Sig.
Nut
Cold
Hot
Ethanol
0.999
0.999
0.999
0.998
0.998
0.998
0.998
0.998
0.998
0.01±0.40
0.01±0.40
0.01±0.40
0.92±0.01
0.92±0.01
0.92±0.01
O=0.01+0.21(M)
O=0.01+0.21(M)
O=0.01+0.21(M)
87.847
87.847
87.847
0.0001
0.0001
0.0001
Stem bark
Cold
Hot
Ethanol
0.994
0.998
0.979
0.987
0.996
0.959
0.987
0.995
0.956
-9.67±1.28
-11.54±0.76
-3.27 ±2.09
1.02±0.03
1.05±0.02
0.92 ±0.05
O=-9.67+1.28(M)
O=-11.54+1.05(M)
O=-3.27+2.09(M)
32.005
55.426
17.378
0.0001
0.0001
0.0001
Root bark
Cold
Hot
Ethanol
0.994
0.998
0.968
0.988
0.995
0.938
0.987
0.995
0.933
-13.80±1.34
-12.21±0.84
-7.28 ±2.74
1.07±0.03
1.05±0.02
0.95 ±0.07
O=-13.80+1.07(M)
O=-12.21+1.05(M)
O=-7.28+0.95M)
33.044
50.973
13.996
0.0001
0.0001
0.0001
Leaf bark
Cold
Hot
Ethanol
0.991
0.999
0.975
0.982
0.998
0.950
0.981
0.997
0.947
-16.70±1.74
-13.11±0.60
-11.97±2.64
1.10±0.04
1.07±0.02
1.02 ±0.06
O=-16.70+1.10(M)
O=-13.11+1.07(M)
O=-11.97+1.02(M)
26.685
72.460
15.771
0.0001
0.0001
0.0001
Note: Ad (R
2
): adjusted R
2
value; K: constant; S.E: standard error; R
c
: regression coefficient; R
E
: regression equation
3 Discussion
The result obtained in this research showed that all the parts of
A. occidentale
have insecticidal properties and
their effectiveness varied with their extraction method, concentration used and period of application. All the parts
of the plant recorded high mortality of the insect irrespective of their extraction method. The ethanolic extracts of
the plant however, appeared more effective than the hot water extract and cold extract of the plant. Also, it was
observed that the nut of the plant was more effective than the three other parts of the plant regardless of the
extraction method used. The probit regression analysis however showed that the ethanolic extract of the nut was
the most effective extract of the plant as it required the lowest concentration to achieve 50 and 95% death of the
insect within 72 h post treatment. The high mortality of the insect recorded by the ethanolic extract of the plant
parts could be due to the ability of the ethanol to dissolve the phytochemicals present in the plant parts as
suggested by Ashamo and Ogungbite (2014). Neoliya et al. (2007) and Al-Qahtani et al. (2012) reported that the
effectiveness of plant materials varied with respect to the part of the plant and the extraction method used. Epidi
and Udo (2009) opined that the degree of effectiveness of botanical extract varied with the type of solvent used for
their extract because different solvents have different degree at which that can extract the active compound present
in the botanicals. Ashmo et al.
(2013) reported variation in the potency of
Newbouldia laevis
parts on
C.
maculatus.
These authors reported that the variation in the potency of
N. laevis
parts could be due to the varying
phytochemicals present in the them. Tannin, saponins, alkaloid and flavonoid have been reported as the major
phytochemicals present in different parts of
A. occidentale
but in different proportion (Fazali et al., 2011).
However, alkaloid, tannin and saponin are being reported of being absent in the leaf extract of
A. occidentale
(Fazali et al., 2011) and could be the major reasons why the leaf extract of
A. occidentale
was not as effective as
other parts regardless of the extraction method used. It has been known that adult
C. maculatus
don’t feed thus
lead to their short life sperm. However, if being provided with sugary substance they can feed and live for longer
period. Therefore, the high mortality of the beetle recorded by the extracts of
A. occidentale
reflected that the
extracts have no sugary substance upon which the insect can feed on, hence lead to their starvation. Botanicals
have been known for their ability to block the voltage-gated sodium channels in the nerve axons or electron
transport chain (in the mitochondrion, leading to inhibition of energy production) (Hollingworth et al., 1994;
Schmutter, 2002; Isman, 2006; Zibaee, 2011). So, the high insect mortality recorded in this work could be due to
ability of the extracts from different parts of the plant to cause total knockdown of the insect or inhibit the
production of energy in the insect. Also, these extracts may have blocked the breathing pores (spiracle) on the
insect and thereby caused asphyxiation and subsequent death of the insect. The result obtained on mortality of the
insect was in agreement with the findings of Ashamo et al. (2013) in which different botanicals extracted with
