Seasonal differences in abundance and distribution of cocoa-pollinating midges in relation to flowering and fruit set between shaded and sunny habitats of the La Lola cocoa farm in Costa Rica
The distribution and abundance of adults and immature stages (larvae and pupae) of cocoa-pollinating midges (Diptera: Ceratopogonidae) was experimentally investigated in shaded and sunny habitats of the La Lola Cocoa Farm in Costa Rica in relation to phenological patterns of flowering and fruit set on cocoa trees. The region experiences a mild dry season between February and March each year. The hypothesis that there should exist seasonally-related fluctuations in the diversity and abundance of midges in both habitats and that there may not be synchrony between cycles of pollinator abundance and periods of maximal flowering in cocoa was explored. Monthly records of tagged cocoa trees revealed that peaks of flowering occurred in both habitats late in the dry season and through the middle of the rainy season, with a marked decline in flowering late in the rainy season. Overall flower production is considerably higher in the sunny habitat than in the shaded habitat although levels of fruit set (new pods) are very similar. By using an experimental design in which replicated treatments of various breeding substrates (leaf litter, litter in artificial bromeliads, cocoa pod husks, and discs of rotting banana tree trunks) were deliberately distributed in both habitats over a 17-month period, it was discovered that midge population densities are greatest in rotting banana tree trunk discs and with greatest densities attained in the dry season in both habitats, but retained at a similarly high level in the shaded habitat to the middle of the subsequent rainy season. Two of the most abundant midge species in the treatments, Forcipomyia youngi Wirth and F quatet Wirth, the former a species new to science, were demonstrated to be effective cocoa pollinators. The absence of well developed shade cover in the sunny habitat intensifies the negative effect of the dry period on midge population dynamics while such an impact is less pronounced in the shaded habitat. A comparison of fruit set on individual cocoa trees near and away from places where midge densities were greatly increased fails to demonstrate statistically a positive correlation between increased pollinator abundance and fruit set, although the trend towards such a relationship is clearly evident. The use of discs of rotting banana tree trunks throughout the year in a cocoa farm such as La Lola provides a very effective means of managing pollinators as well as providing a mechanism by which pollinator populations can thrive during the dry season and therefore pollinate more cocoa flowers when a burst of flowering commences late in the dry season. Otherwise, the dry season may be a limiting factor of pollinating midge populations, particularly when shaded cover is not well developed.
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| Format: | biblioteca |
| Language: | eng |
| Published: |
Londres (RU): British Ecological Society,
1983
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| Subjects: | THEOBROMA CACAO, ERYTHRINA, FORCIPOMYIA, PLANTACION, PLANTAS DE SOMBRA, AGROFORESTERIA, POLINIZADORES, INSECTA, CICLO VITAL, DINAMICA DE POBLACIONES, FENOLOGIA, VARIACION ESTACIONAL, FLORACION, COSTA RICA, |
| Online Access: | https://doi.org/10.2307/2403127 |
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