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Signatura:Thesis H557i
Autor:Hernández B, J.
Aut.Corporativo:University of Wisconsin (EUA)
Título:Insect pollination of cacao (Theobroma cacao L.) in Costa Rica.
Idioma: En.
Grado acad.: Tesis (Ph D)
P. imprenta:Wisconsin (EUA). 1965. 167 p..
Notas:Ilus. 21 tab. Bib. p. 162-167. Sum. (En).
Resumen1:The insects associated with cacao flowers in Costa Rica were studied with particular reference to their effectiveness as pollinators. The species most commonly found in the flowers at Turrialba and La Lola were the thrips, Frankliniella parvula Hood, and the aphid, Toxoptera aurantii B. de Fons. Other species such as the aphid, Aphis gossypii Glov., the ants, Wasmannia auropunctata (Roger), and Solenopsis geminata (F.), and the bee, Trigona jaty Sm. occasionally visited the flowers. With the exception of the latter species, these insects naturally carried very low numbers of pollen grains on their bodies, and their activity in and around the flowers suggested that they were not well adapted to pollinate cacao flowers. T. jaty, on the other hand, habitually worked the flower to obtain the pollen from the anthers, but the importance of this insect in cacao pollination is probably nil. The pollen, carried on their hind legs, had a very low percentage of viability and was not deposited on the stigma. Among the several United Fruit clones tested for compatibility, UF-221 had the highest percentage (82 percent) of self-compatibility and was therefore used in caged insect pollination experiments. The highest percentage of pollination in various experiments with different numbers of insects per cage was: S. geminata 20 percent, Solenopsis (Diplorhoptrum) sp. 3.5 percent, W. auropunctata 8 percent, T. aurantii 28 percent, F. parvula 1 percent, T. jaty 3 percent. However, with only one Forcipomyia spp. per cage 52 percent pollination resulted. Pollination by these insects, except that of Forcipomyia spp., was considered accidental and inadequate as judged by the very low numbers of pollen grains deposited on the stigmas. On the contrary, flowers pollinated by Forcipomyia spp, in cages had far higher numbers of pollen grains (175 average) on the stigmas than that necessary for the proper fertilization (30 to 40 ovules) of a cacao flower. From 1971 to 1963 Forcipomyia midges (which are considered the main pollinators of cacao in most cacao-growing countries) were never observed on cacao flowers in Costa Rica and evidence of their existence, by the examination of flower stigmas, was not obtained. Continued search, however, revealed the presence of Forcipomyia specimens in cacao flowers in July of 1964. Also at this time flowers typically pollinated by this insect were observed. Over 350 specimens of Forcipomyia adults were collected by observing cacao flowers until a midge was discovered and then enclosing the flower in a vial. A preliminary taxonomic determination has shown the existence of several genera and species in this collection. Berlesse funnel extractions of decaying matter from cacao plantations yielded low numbers of Forcipomyia larvae. The population intensity of Forcipomyia was estimated by the number of flowers typically pollinated by these midges. Plots with scarse flowering had the highest intensity of midges in relation to the number of flowers available. The percentage of pollination taking place was 0.9 percent when Forcipomyia pollination was desregarded but 2.9 percent when it was included. Thus they accounted for twice as much pollination as that by all other natural means taking place in the area studied. Quantitative figures on the way that Forcipomyia midges visited cacao flowers, as well as their effectiveness as pollinators of cacao in the field were obtained. Sixty-six per cent of the midges were actually observed to deposit pollen on the flower stigma. This took place while the midge was walking and probing downward on the inner surface of a staminode. Seventy-nine per cent of the midges entered the petal pouches where pollen gathered on their nota. The space between the stigma and the staminodes appears to be exactly right to allow the passage of the insect but not their load of pollen grains which is deposited on the stigma as they pass. The effectiveness of pollination by Forcipomyia midges was 74 percent, as estimated by the number of fertilized flowers as a consequence of midge visitation, an average of 395 pollen grains were found on the stigmas of these flowers. It was concluded that Forcipomyia midges were by far the most important pollinators of cacao in areas where they were observed. Wild Forcipomyia females, collected while visiting cacao flowers, were kept alive under laboratory conditions for an average of 12.7 days feeding on 20 percent sucrose. Feeding studies suggested that midges in the field probably visit and feed on cacao flowers for a very specialized and small quantity of nutrients. Forcipomyia eggs hatched in about 3 days and the larvae were reared to pupation in about 13 days on malt-agar medium inoculated with washings from decaying matter. The pupal stage was completed in about 3 days. Laboratory obtained females lived for an average of 13.3 days feeding on 20 percent sucrose, while males survived for only 5.5 days. No viable eggs were obtained from virgin females or from females kept in pairs with males, which was attributed to lack of copulation. Mass rearing attempts showed very promising results. Several generations were obtained in a cage showing that mating had taken place, however, only low numbers of insects were obtained in each generation. Apparently the entire life cycle of Forcipomyia midges was completed in about 27 days.

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