The Population Dynamics Of Thr Brown Cocoa Mirid, SahlbergellaSingularis Haglund In Ibadan, Nigeria
2010
The brown cocoa mirid, Sahlbergella singularis Haglund has been
adjudged the most economically important insect pest of cocoa across
West African the sub-region. The pest is capable of causing yield loss
of about 30% in the first cocoa growing season and up to 70% yield loss
in not less than two cocoa seasons if not controlled. This paper
presents the population dynamics of S. singularis in Ibadan, Nigeria
and the interactions between field populations of mirids and density
dependent (natural enemies) and density independent (weather
parameters) factors. One hundred mature cocoa trees were randomly
sampled from base to 1.5m Girth at Breast Height (GBH) fortnightly on a
two hectare plantation for adult S. singularis and its natural enemies
(Camponotus species, Crematogaster brevispinosa, Oncophylla longinoda,
Acantholepis capensis and Palothyreus tarsatus) using standard pr°
Cedures. Mirid population and natural enemy abundance were correlated
to monthly weather parameters (Temperature, Relative humidity and
Rainfall). The population dynamics followed a similar trend over a
period of three years of study. The population of the pest rapidly
built-up in August of each month and this coincided with the period of
the main cropping season of cocoa, as cocoa trees were in massive pod
production. Weather parameters such as temperature and relative
humidity played a major role in the fluctuations of mirid population.
Rainfall did not seem to have any impact on the pest dynamics. Peak
relative humidity data of 88.2%, 84% and 83.5% were recorded in August
2004, 2005 and 2006, respectively and the temperature readings declined
around this period, inadvertently favouring the multiplication of mirid
numbers in the field. The roles of density-dependent factors, that is,
natural enemies, were observed in the field and reported. Ants of
various genera were observed to exert different degrees of predation in
the field, however, there were no parasitoids encountered both in the
field and laboratory throughout the period of this study. Knowledge of
the seasonal abundance of the pest is important to generate enough
background information needed for effective control of mirid in
Nigeria.
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