International Journal of Horticulture, 2017, Vol.7, No. 9, 64-75
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different effects against insects (Ashamo et al., 2013). Extraction methods have been opined to have significant
effect on botanical insecticides (Ashamo and Ogungbite, 2014; Akinneye and Ogungbite, 2016).
Anacardium
occidentale (Linn.) is a medicinal plant which has been used for the treatment of many diseases
(Fazali et al., 2011). It belongs to the family anacardiaceae. It has been proven insecticidal against wide range of
insects. Ileke and Olotuah (2012) reported its insecticidal potential against
Callosobruchus maculatus.
However,
the comparative efficacy of the different parts of the plant extracted with different methods has not been well
established. Therefore, there is necessity to investigate the effect of extraction methods on the efficacy of different
parts of the plant. This present work investigated the effect of different extraction methods on the biocidal efficacy
of different parts of
Anarcadium occidentale
against
Callosobruchus maculatus
infestation on cowpea.
2 Results
2.1 Percentage mortality of
C. maculatus
treated with different concentrations of different parts of
A.
occidentale
The effect of different parts of
A. occidentale
extracts on the survival of
C. maculatus
on protected cowpea seeds
were presented in Table 1. There were statistically significant differences within and between the treatments
throughout the period of observation. The mortality of the insect was the function of the part of the plant used, the
extraction method, the concentrations of the extract and the period of application. The ethanol extract (4%
concentration) of the nut achieved the highest mortality of 46% within 24h post treatment and it was significantly
different from others at F= 79.058, df= 48, 98, p < 0.0001 except 3% and 4% ethanolic extract of the nut and the
stem bark which respectively recorded 43 and 44% mortality of the insect. At 48 and 72 h post treatment, ethanol
extract of the nut recorded the highest mortality of 67.67 and 75.33% mortality respectively and were significantly
different from other treatments at F= 93.943, df= 48, 98, p < 0.0001 (48 h) and F=89.389, df=48, 98, p <
0.0001(72). Irrespective of the extraction method and concentration used, the nut of the plant significantly
affected the survival of the insect than other parts. Also, making the plant parts and the concentrations used
constant, ethanolic extract of the plant recorded high mortality of the beetle compared to cold extract and hot
extract of the plant. At 96h post treatment, only ethanolic extract of the nut achieved 100% mortality and its effect
was significantly different from other treatments at F= 101.751, df= 48, 98, p < 0.0001. There was significant
difference between the control and the plant parts regardless of the period of exposure. Table 2 showed the
interactive effect of the plant part, extraction method used and the concentration of the oils on survival of the
insect. There was significant interactive effect between the plant part used, the extraction method used and
concentration on the mortality of the insect.
2.2 The lethal concentration required to achieve 50 and 95% mortality of C. maculatus by the extract of A.
occidentale within 72 h post treatment.
Table 3 showed the estimated concentration of extract of different parts of
A. occidentale
required to achieve 50
and 95% mortality of
C. maculatus
within 72 h post treatment. The dosage required varied with the plant part used
and the extraction method. With the extraction method being constant, nut extracts appeared most effective among
the plant part used as reflected by their Fiducial limits. Thus, the order of effectiveness of the extracts in term of
the plant part used could be arranged as nut > stem > root > leaf. Nevertheless, irrespective of the plant part used,
the ethanol extracts of the plant appeared most effective as reflected by their Fiducial limits. Hence, the order of
effectiveness of the plant in term of extraction method could be arranged as ethanol > hot > cold extraction. The
ethanolic extract of the
A. occidentale
nut was the most effect extract of the plant as it required only 0.42%
(0.09-0.75%) and 1.00 % (0.82-1.56%) to achieve 50 and 95% mortality of the beetle within 72 h of application.
However, the chi square values that were greater than 3.81 reflected high level of relationship between the
concentration used and the mortality of the insect except leaf extracted by hot water which had a chi square value
of 3.20. The relationship between the concentrations of the extracts and the mortality of the insect was significant
as reflected by the p-values of the chi square at df=13, p < 0.0001 except the leaf extracted by hot water (df= 13, p
< 0.07).
