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Seasonal population changes in cocoa capsids (Hemiptera, Miridae) in Ghana

Published online by Cambridge University Press:  10 July 2009

D. G. Gibbs
Affiliation:
International Capsid Research Team, Cocoa Research Institute of Ghana, Tafo
A. D. Pickett
Affiliation:
International Capsid Research Team, Cocoa Research Institute of Ghana, Tafo
Dennis Leston
Affiliation:
International Capsid Research Team, Cocoa Research Institute of Ghana, Tafo

Extract

Pupulations of the West African cocoa capsids Distantiella theobroma (Dist.) and Sahlbergella singularis Hagl. were sampled in 1966–67 by several methods: fast knockdown over sheets with pyrethrum, mercury-vapour light-trap, direct counts in a small artificially established area of high population, and observations of presence or absence in randomly selected inspection squares.

A population build-up in mature cocoa accompanies and probably directly depends on development of the main crop from July or August to October. When pods become scarce after harvesting there is in S. singilaris a period of dispersal in which the species becomes more widespread as feeding is transferred to vegetative tissues, and in D. theobroma a more local change of feeding sites.

Subsequent events vary greatly between areas and between years. It is suggested that the extent to which capsids are able to utilise vegetative tissues varies and depends on nutritional changes in the external parenchymatous tissues from which their food is obtained.

Low humidities during spells of harmattan in January and February almost certainly kill larvae in exposed situations, but feeding conditions following such periods may be particularly favourable to capsids as large rapid population increases can occur locally. The factors involved are obscure but may be related to processes of regeneration stimulated by leaf loss and other damage in dry conditions.

The densities and seasonal patterns found are discussed in relation to results of previous workers and some implications for control briefly considered.

Type
Research Paper
Copyright
Copyright © Cambridge University Press 1968

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