International Journal of Horticulture, 2018, Vol.8, No.1, 1-7
3
daily for 4 days. Dead beetles were those who neither moved nor respond to pin probing. Percentage adult
mortality was corrected using Abott’s formula (Lale, 2006) thus:
Where P
T =
corrected mortality (%); P
O=
observed mortality (%); P
C=
control mortality (%)
1.4 Effect of plant powders on oviposition and adult emergence of
C. maculatus
Twenty grammes (20 g) of clean and uninfested cowpea seeds of susceptible Ife brown variety was weighed into
160 ml plastic cups. Then 0.2 g, 0.4 g, 0.6 g, 0.8 g and 1.0 g of various plant powders were weighed and
thoroughly mixed with the 20 g of disinfested seeds. The seeds in the control contained no plant powders. Five (5)
pairs (5 male: 5 female) of adult
C. maculatus
(0-2 day old) sexed according to the methods described by
Odeyemi and Daramola (2000) were introduced into the treated and untreated (control) cowpea seeds. Male
C.
maculatus
have comparative shorter abdomen and the dorsal side of the terminal segment is sharply curved
downward and inward. In contrast, the females have comparative longer abdomen and the dorsal side of the
terminal segment is only slightly bent downward. The females also have two dark visible sports on their elytra
(Odeyemi and Daramola, 2000). Four replicates of the treated and untreated control were laid out in Complete
Randomized Block Design. The plastic cups were covered with muslin cloth to let in but prevent the escape of
beetles (Jambere
et al
., 1995). The experiments were left for 7 days for the insects to oviposit. The total number
of eggs laid by
C. maculatus
on cowpea seeds were counted and recorded after allowing the insects to lay eggs
for 7 days. The Percentage adult emergence was calculated as described below:
1.5 Statistical analysis
Data obtained from all the parameters were subjected to one-way analysis of variance at 5% significant level and
means were separated with New Duncan’s Multiple Range Tests using SPSS version 17. In addition, data
obtained from beetles’ mortality were subjected to regression analysis to calculate the LD
50
and LD
95
of the
powders after 96 h of application using probit analysis.
2 Results
2.1 Effect of
S. longepedunculata
powders on mortality of
C. maculatus
Beetle mortality of
C. maculatus
on cowpea seeds treated with the plant powders
S. longepedunculata
is
presented in Table 1. Adult mortality in the treated cowpea was significantly (P<0.05) different from beetle
mortality in the control. The percentage adult mortality remained 0% in the control experiment throughout the
period of exposure. However, low insect mortality was observed in all the treatments after 72 h of application.
The highest beetle mortality of 71.25% was recorded in cowpea seeds treated with the root bark at the highest
dosage of 1.0 g within 96 h of application and it was significantly different from beetle mortality of 65.0% and
46.25% in cowpea seeds treated with the powders of
S.
longepedunculata
stem bark and leaf at the same
concentration and period of exposure.
2.2 Lethal dose (LD
50
and LD
95
) of plant powders required to achieve 50% and 95% mortality in
C.
maculatus
after 96 h post treatment
The lethal dose (LD
50
) and (LD
95
) of the plant powders is presented in Table 2. The result obtained indicated that
to achieve 50% and 95% mortality in the beetle, the plant powders must be applied at higher dosage except the
powder obtained from the root bark in which low dosage is required for 50% (2.56-4.01) and 95% (5.10-6.45).
The powder obtained from leaf appeared to be the least effective as indicated by their amount of dosages required
to cause 50% (3.53-7.01) and 95% (8.34-11.14) mortality.
