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Insect Phenology in a Forest Cocoa-Farm Locality in West Africa

D. G. Gibbs and Dennis Leston
Journal of Applied Ecology
Vol. 7, No. 3 (Dec., 1970), pp. 519-548
DOI: 10.2307/2401976
Stable URL: http://www.jstor.org/stable/2401976
Page Count: 30
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Insect Phenology in a Forest Cocoa-Farm Locality in West Africa
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Abstract

Sampling by light trap, insecticide knockdown and other methods has given data on seasonal population changes in many insects and a few spiders in an area of semideciduous high forest largely devoted to cocoa growing at Tafo, Ghana. Populations of most species showed seasonal change and in every month some species were in a period of major increase. There are several characteristic seasonal population curves which, when associated with botanic and climatic events, lead to the conclusion that six seasons should be recognized. These can be defined by a combination of mean rainfall (more or less than 4 in./month) and mean monthly sunshine (more or less than 5.5 h/day). The seasons, listed together with some of the events we have discussed, are: (1) Dry sunny. Maximum fruit production, abundance of fruit-feeding and seed-feeding insects, continuing into the following season. Species thought to be favoured by effects of drought and related stress factors on host-plant nutrition also increase. (2) First wet sunny. Maximum leaf production; abundance of leaf-feeding insects and their predators. Maximum breakdown of leaf litter; abundance of litter-feeding and fungus-feeding insects. (3) First wet dull. Decline in leaf feeders and their predators. Abundance of timberborers. (4) Dry dull. Biologically similar to wet dull seasons; forms with numbers closely correlated with rainfall, for example timber-borers, may decline. (5) Second wet dull. (6) Second wet sunny. Shorter than the first wet sunny season, but period of submaximum leaf production; abundance of leaf feeders and their predators. Species that depend for food on primary production of plant tissues in the form of leaves or fruits have maximum numbers in the three sunny seasons. Their populations appear to respond directly to seasonal changes in the amount of food.

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