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An Investigation into the Effect of Cultural Conditions on Populations of the Vectors of Virus Diseases of Cacao in Ghana with an Evaluation of seasonal Population Trends

Published online by Cambridge University Press:  10 July 2009

P. B. Cornwell
P. B. Cornwell
Affiliation:
West African Cocoa Research Institute, Tafo, Ghana.
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Summary

A comparison is made of the populations of mealybugs, ants, predators and parasites on cacao growing in dense secondary bush and under well-cultivated conditions in Ghana, West Africa. The percentage of cacao trees infested (termed the infestation rate), the number of colonies and the populations of the vectors were similar under the two cultural conditions. Populations of ants of the genus Crematogaster and of COCCINELLIDAE were higher in bush areas than in cultivated ones. Populations of ants of the genus Pheidole, though smaller than those of Crematogaster, were greater in areas of well-maintained cacao.

Correlations of infestation rates and populations were compared under the two cultural conditions for mealybugs, ants, predators and parasites. The field data showed an exponential relationship between these factors, which was rendered linear by suitable transformations. The correlation of mealybug populations with infestation rate and with populations of parasites and predators was equally high in both habitats. The correlation of mealybug populations with those of Crematogaster was closer in the bush than in well-maintained cacao, but the implications of this are not fully understood.

There was a higher infestation rate of cacao during the first three months of the year. In contrast with previous work, the present survey has demonstrated significant changes in the vector population during the year, of a five- or six-fold order. These seasonal changes are based on mean mealybug populations per infested tree, and were largely the result of changes in the numbers of colonies; populations showed a decline during the first six months of the year and then rose to a maximum during October–November. The data suggest that these trends may be brought about largely by changes in the abundance of predators and parasites.

Type
Original Articles
Information
Bulletin of Entomological Research , Volume 48 , Issue 2 , June 1957 , pp. 375 - 396
Copyright
Copyright © Cambridge University Press 1957

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