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Evaluation of the toxicity
of Actara 25 WG for the control of the cocoa mirid
Sahlbergella singularis Hagl. (Hemiptera: Miridae) in
Nigeria
J.C. Anikwe, E.U. Asogwa*, T.C.N. Ndubuaku and F.A.
Okelana
Crop
Protection Division, Cocoa Research Institute of Nigeria,
Ibadan, Nigeria.
*Corresponding author. E-mail:
ucheasogwa1@yahoo.com.
Accepted
23 January, 2009 |
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In Nigeria, the brown cocoa mirid Sahlbergella singularis
is responsible for over 30% yield loss in cocoa.
Insecticides still remain a very important component among
the strategies for effective control of major insect pests
of cocoa in Nigeria. The Cocoa Research Institute of Nigeria
(CRIN) has the “National Mandate” to evaluate and recommend
new insecticides for use on cocoa in Nigeria. The mortality
rates of mirids on exposure to the various concentrations
(0.01, 0.013, 0.015 and 0.02%) of Actara 25 WG increased
with period of exposure of the mirids in the laboratory.
Both Actara and the Standard Miricide were similar at 0.020%
concentration as both gave a 100% kill of mirids at the 90th
min. No mortalities were recorded in control cages
throughout the exposure period. The insecticide did not
produce any adverse side effects on cocoa seedlings and
mature plants sprayed with the various concentrations over
the years. The relative toxicity of the insecticide at the
four different concentrations to adult mirids, 24 h after
the first field treatment application, was 93.3, 82.4, 81.8
and 100% adult mortality, respectively. In the case of the
nymphal mirids, percentage mortality was 89.6, 81.5, 86.8
and 94.3% for the various concentrations, respectively. The
population of both the adult and nymphal mirids crashed to
almost zero (0) in most cases suggesting about 100%
mortality 24 h after the second spraying on the residual
mirid populations. Mirid numbers remained so low until the
third spray application after which it was unnecessary to
spray the sub-plots, thereafter. Spraying of mature and
fruiting cocoa farms at application rate of 0.015% was found
adequate and recommended taking into consideration the
impact of the product on the environment and for economic
reasons.
Key
words:
Mortality, concentration, insecticide, spraying, miricide,
exposure. |
