Abstract
Laboratory bioassays were conducted on five-selected aqueous plant extracts for contact toxicity and residual action on the brown cocoa mirid, Sahlbergella singularis. The extracts wereMangifera indica (leaf), Anacardium occidentale (leaf), Ocimiun gratissimun (leaf), Azadirachta indica (stem bark) and Acalypha wilkesiana (leaf). Leaf extracts of M. indica, A. wilkesiana and stem bark extract of A. indica applied at 1:5% w/v gave an effective kill of 100, 80 and 80%, respectively, for contact toxicity. M. indica aqueous extract recorded a 100% mirid mortality at the three concentrations tested for 24 h post treatment for residual action, while A. indica gave 89% mortality of mirids at 1:5% w/v. Neem extract was observed to be slow acting. Extracts ofA. occidentale was not efficacious and treatment was not significantly different from that of control (water) at 5% probability level. Key words: Laboratory bioassay, brown cocoa mired, aqueous plant extracts, toxicity.
Highlights
Cocoa, Theobroma cacao Linnaeus, 1753, belongs to the family Sterculiaceae (Coste, 1992) and its cultivation in Nigeria dates back to 1874 when a local chief (SquissIbaningo) established a plantation at Bonny in the eastern region
Gratissimum, A. wilkesiana and bark of A. indica were obtained from the forest zone of the Cocoa Research Institute of Nigerian (CRIN)
Leaf extracts of M. indica, A. wilkesiana and stem bark extract of A. indica applied at 1:5% w/v gave an effective kill of 100, 80 and 80%, respectively (Table 1)
Summary
Theobroma cacao Linnaeus, 1753, belongs to the family Sterculiaceae (Coste, 1992) and its cultivation in Nigeria dates back to 1874 when a local chief (SquissIbaningo) established a plantation at Bonny in the eastern region. In 1887, the government sent seedlings from the old botanical garden at Ebute-meta (Lagos) up country (Ibadan) for trials. This explains why cacao cultivation gained its first impetus around Ibadan and the western states of Nigeria (Opeke, 1992; Anikwe et al, 2009). Nigeria reported her first cocoa export in 1900 (Opeke, 1992). Nigeria’s cocoa production continued to soar and by 1965, it had become the second largest producer in the world with an annual output of about 270,000 tonnes.
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