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Field Observations on the Cacao Mirids Sahlbergella singularis Hagl. and Distantiella theobroma (Dist.), in the Gold Coast. PART II. Geographical and Habitat Distribution

Published online by Cambridge University Press:  10 July 2009

G. Williams
G. Williams
Affiliation:
The Zoology Department, The University, Reading.
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Extract

The geographical ranges of Sahlbergella singularis and Distantiella theobroma overlap, and the Gold Coast lies in the zone common to both. The respective northern limits remain to be determined, and should be investigated to the north of the main cacao belt, from Kintampo to the Afram plain.

The same area should also yield information on the possible importance of alternative hosts in the dispersal of cacao Mirids, as the small stands are well separated from each other.

Earlier records, that D. theobroma is confined to seedlings and S. singularis to mature trees, are erroneous. D. theobroma is found on pods and, particularly, chupons. The feeding range of S. singularis includes fan branches in addition, but breeding is confined to chupons and pods.

Observations suggest that there is competition for breeding sites on chupons. Of the many chupons in an area only a small number is available to Mirids, and the proportion of nymphs reaching maturity is limited by their sedentary habit and the destructiveness of their feeding.

Co-existence of the two species is possible by their slightly different habits. S. singularis produces more eggs, but is more diffusely distributed. D. theobroma is virtually restricted to chupons, but can quickly build up a large population in favourable areas by its greater rate of egg production.

In Nigeria, the rate of egg production by D. theobroma is less than that by S. singularis, and this, together with the sparsity of chupons, may account for the unimportance of D. theobroma in that country.

Type
Original Articles
Information
Bulletin of Entomological Research , Volume 44 , Issue 3 , September 1953 , pp. 427 - 437
Copyright
Copyright © Cambridge University Press 1953

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References

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