The population dynamics of the brown cocoa mirid, <i>Sahlbergella singularis</i> haglund in Ibadan, Nigeria

Abstract

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 procedures. 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 2004August , 2005August 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.

Optimizing mirid control on cocoa farms through complementary monitoring systems

“…This is a couple of months earlier than reported in the major producing countries in West Africa (Padi and Owusu ; Anikwe et al. ). Between June and July 2012, there was a significant increase in the number of adult mirids in traps, due to the progression of nymphs seen in April/May.…”

“…The visual hand-height assessment method indicated that mirid populations (predominately nymphs) began to increase rapidly in April with an initial peak in May, followed by a rapid build-up in June. This is a couple of months earlier than reported in the major producing countries in West Africa (Padi and Owusu 1998;Anikwe et al 2010). Between June and July 2012, there was a significant increase in the number of adult mirids in traps, due to the progression of nymphs seen in April/May.…”

“…High temperatures result in lower population size due to high desiccation risk for mirids because of their soft bodies (Babin et al 2010). Anikwe et al (2010) also noted that mirid populations decline in periods of low humidity. Higher temperature and lower humidity in the West African dry season would also reduce the survival rate of mirids by reducing the amount of water in feeding sites and the availability of suitable feeding and breeding sites.…”

Effects of cocoa tree phenology and canopy microclimate on the performance of the mirid bug Sahlbergella singularis

“…The patterns of these fluctuations are similar throughout west and central Africa, with one peak between August and December, depending on the location (Lavabre et al, 1962;N'Guessan & Coulibaly, 2000;Anikwe et al, 2010). The patterns of these fluctuations are similar throughout west and central Africa, with one peak between August and December, depending on the location (Lavabre et al, 1962;N'Guessan & Coulibaly, 2000;Anikwe et al, 2010).…”

“…Sahlbergella singularis populations display sharp seasonal fluctuations on cocoa. The patterns of these fluctuations are similar throughout west and central Africa, with one peak between August and December, depending on the location (Lavabre et al, 1962;N'Guessan & Coulibaly, 2000;Anikwe et al, 2010). The largest populations of cocoa mirid usually overlap various climatic seasons and seem to coincide with the cocoa fruiting period (Entwistle, 1972;Bruneau de Miré, 1977).…”